RESUMEN
BACKGROUND: The molecular basis of the incipient stage of speciation is still poorly understood. Cichlid fish species in Lake Victoria are a prime example of recent speciation events and a suitable system to study the adaptation and reproductive isolation of species. RESULTS: Here, we report the pattern of genomic differentiation between two Lake Victoria cichlid species collected in sympatry, Haplochromis pyrrhocephalus and H. sp. 'macula,' based on the pooled genome sequences of 20 individuals of each species. Despite their ecological differences, population genomics analyses demonstrate that the two species are very close to a single panmictic population due to extensive gene flow. However, we identified 21 highly differentiated short genomic regions with fixed nucleotide differences. At least 15 of these regions contained genes with predicted roles in adaptation and reproductive isolation, such as visual adaptation, circadian clock, developmental processes, adaptation to hypoxia, and sexual selection. The nonsynonymous fixed differences in one of these genes, LWS, were reported as substitutions causing shift in absorption spectra of LWS pigments. Fixed differences were found in the promoter regions of four other differentially expressed genes, indicating that these substitutions may alter gene expression levels. CONCLUSIONS: These diverged short genomic regions may have contributed to the differentiation of two ecologically different species. Moreover, the origins of adaptive variants within the differentiated regions predate the geological formation of Lake Victoria; thus Lake Victoria cichlid species diversified via selection on standing genetic variation.
Asunto(s)
Cíclidos/genética , Especiación Genética , Animales , Secuencia de Bases , Flujo Génico , Genoma , Genómica , Lagos , Polimorfismo Genético , Especificidad de la Especie , SimpatríaRESUMEN
BACKGROUND: For Lake Victoria cichlid species inhabiting rocky substrates with differing light regimes, it has been proposed that adaptation of the long-wavelength-sensitive (LWS) opsin gene triggered speciation by sensory drive through color signal divergence. The extensive and continuous sand/mud substrates are also species-rich, and a correlation between male nuptial coloration and the absorption of LWS pigments has been reported. However, the factors driving genetic and functional diversity of LWS pigments in sand/mud habitats are still unresolved. RESULTS: To address this issue, nucleotide sequences of eight opsin genes were compared in ten Lake Victoria cichlid species collected from sand/mud bottoms. Among eight opsins, the LWS and rod-opsin (RH1) alleles were diversified and one particular allele was dominant or fixed in each species. Natural selection has acted on and fixed LWS alleles in each species. The functions of LWS and RH1 alleles were measured by absorption of reconstituted A1- and A2-derived visual pigments. The absorption of pigments from RH1 alleles most common in deep water were largely shifted toward red, whereas those of LWS alleles were largely shifted toward blue in both A1 and A2 pigments. In both RH1 and LWS pigments, A2-derived pigments were closer to the dominant light in deep water, suggesting the possibility of the adaptation of A2-derived pigments to depth-dependent light regimes. CONCLUSIONS: The RH1 and LWS sequences may be diversified for adaptation of A2-derived pigments to different light environments in sand/mud substrates. Diversification of the LWS alleles may have originally taken place in riverine environments, with a new mutation occurring subsequently in Lake Victoria.
Asunto(s)
Adaptación Ocular , Cíclidos/fisiología , Percepción de Profundidad/fisiología , Proteínas del Ojo/metabolismo , Sedimentos Geológicos , Lagos , Pigmentación/genética , Alelos , Animales , Secuencia de Bases , Color , Evolución Molecular , Geografía , Masculino , Especificidad de la EspecieRESUMEN
Gar is an actinopterygian that has bone, dentin, enameloid, and ganoin (enamel) in teeth and/or scales. Mineralization of these tissues involves genes encoding various secretory calcium-binding phosphoproteins (SCPPs) in osteichthyans, but no SCPP genes have been identified in chondrichthyans to date. In the gar genome, we identified 38 SCPP genes, seven of which encode "acidic-residue-rich" proteins and 31 encode "Pro/Gln (P/Q) rich" proteins. These gar SCPP genes constitute the largest known repertoire, including many newly identified P/Q-rich genes expressed in teeth and/or scales. Among gar SCPP genes, six acidic and three P/Q-rich genes were identified as orthologs of sarcopterygian genes. The sarcopterygian orthologs of most of these acidic genes are involved in bone and/or dentin formation, and sarcopterygian orthologs of all three P/Q-rich genes participate in enamel formation. The finding of these genes in gar suggests that an elaborate SCPP gene-based genetic system for tissue mineralization was already present in stem osteichthyans. While SCPP genes have been thought to originate from ancient SPARCL1, SPARCL1L1 appears to be more closely related to these genes, because it established a structure similar to acidic SCPP genes probably in stem gnathostomes, perhaps at about the same time with the origin of tissue mineralization. Assuming enamel evolved in stem osteichthyans, all P/Q-rich SCPP genes likely arose within the osteichthyan lineage. Furthermore, the absence of acidic SCPP genes in chondrichthyans might be explained by the secondary loss of earliest acidic genes. It appears that many SCPP genes expanded rapidly in stem osteichthyans and in basal actinopterygians.
Asunto(s)
Proteínas de Unión al Calcio/metabolismo , Proteínas de Peces/metabolismo , Peces/genética , Fosfoproteínas/metabolismo , Animales , Proteínas de Unión al Calcio/genética , Proteínas de Peces/genética , Regulación de la Expresión Génica , Variación Genética , Fosfoproteínas/genética , FilogeniaRESUMEN
The study describes >400 major histocompatibility complex (MHC) class II B exon 2 and 114 intron 2 sequences of 36 passerine bird species, 13 of which belong to the group of Darwin's finches (DFs) and the remaining 23 to close or more distant relatives of DFs in Central and South America. The data set is analyzed by a combination of judiciously selected statistical methods. The analysis reveals that reliable information concerning MHC organization, including the assignment of sequences to loci, and evolution, as well as the process of species divergence, can be obtained in the absence of genomic sequence data, if the analysis is taken several steps beyond the standard phylogenetic tree construction approach. The main findings of the present study are these: The MHC class II B region of the passerine birds is as elaborate in its organization, divergence, and genetic diversity as the MHC of the eutherian mammals, specifically the primates. Hence, the reported simplicity of the fowl MHC is an oddity. With the help of appropriate markers, the divergence of the MHC genes can be traced deep in the phylogeny of the bird taxa. Transspecies polymorphism is rampant at many of the bird MHC loci. In this respect, the DFs behave as if they were a single, genetically undifferentiated population. There is thus far no indication of alleles that could be considered species, genus, or even DF group specific. The implication of these findings is that DFs are in the midst of adaptive radiations, in which morphological differentiation into species is running ahead of genetic differentiation in genetic systems such as the MHC or the mitochondrial DNA. The radiations are so young that there has not been enough time to sort out polymorphisms at most of the loci among the morphologically differentiating species. These findings parallel those on Lake Victoria haplochromine fishes. Several of the DF MHC allelic lineages can be traced back to the MHC genes of the species Tiaris obscura, which we identified previously as the closest extant relative of DFs in continental America.
Asunto(s)
Pinzones/genética , Variación Genética , Antígenos de Histocompatibilidad Clase II/genética , Polimorfismo Genético , Secuencia de Aminoácidos , Animales , Duplicación Cromosómica/genética , Análisis por Conglomerados , Evolución Molecular , Exones , Galliformes/genética , Orden Génico , Datos de Secuencia Molecular , Primates/genética , Alineación de SecuenciaRESUMEN
Perch-like fishes of the family Cichlidae are models for the study of speciation. An important tool in these studies is the major histocompatibility complex (Mhc) and its organization. The present study takes the first step toward the elucidation of the Mhc class II gene organization in the tilapiine fish Oreochromis niloticus (Orni). Using class II A- and class II B-specific probes, Mhc-bearing clones were identified and isolated from a bacterial artificial chromosome (BAC) library. The analysis of these clones by a combination of molecular, genetic-mapping, and phylogenetic methods led to the identification of nine class II A and 15 class II B loci. Genes at these loci constitute two families, which we designate as class IIa and class IIb families. Each of the families contains A and B loci. Some genes in both families are expressed and functional. The two families differ in their chromosomal location (they are unlinked) and their mode of evolution. The class IIa family genes are conserved across different teleost taxonomical orders, whereas the class IIb family genes are apparently products of multiple, more recent, rounds of gene duplications. The rounds established at least five monophyletic groups of genes. The founding unit of each monophyletic group might have been a pair of class II A and B loci.
Asunto(s)
Cíclidos/genética , Proteínas de Peces/genética , Antígenos de Histocompatibilidad Clase II/genética , Filogenia , Alelos , Animales , Cromosomas Bacterianos/genética , Cíclidos/clasificación , Clonación Molecular , Mapeo Contig , Proteínas de Peces/clasificación , Orden Génico , Variación Genética , Antígenos de Histocompatibilidad Clase II/clasificación , Datos de Secuencia Molecular , Análisis de Secuencia de ADNRESUMEN
In 1632, King Gustav II Adolphus of Sweden founded Academia Gustaviana,the predecessor of the present Tartu University in Estonia. After the reopening of the University in 1802, the development of the Faculty of Medicine started. The number of outstanding anatomists; Burdach, von Baer, Reichert, Bidder, Reissner, Kupffer, and Rauber made various discoveries at the Anatomical Theater (Theatrum Anatomicum). The present paper acquaints readers with profiles of these anatomists and their main contributions, and attempts to consider reasons of a quick development of Tartu University during rather a short period in the 19th century.
Asunto(s)
Anatomía/historia , Docentes Médicos/historia , Facultades de Medicina/historia , Estonia , Historia del Siglo XVII , Historia del Siglo XVIII , Historia del Siglo XIX , Historia del Siglo XX , Historia del Siglo XXIRESUMEN
Integrin-binding sialoprotein (IBSP) is a member of the small integrin-binding ligand N-linked glycoprotein (SIBLING) family; and the whole SIBLING family is further included in a larger secretory calcium-binding phosphoprotein (SCPP) family. SIBLING proteins are known to construct a part of the non-collagenous extracellular matrices of calcified tissues, and considered to have arisen by duplication and subsequent divergent evolution of a single ancient gene. To understand the alterations of SIBLING molecules associated with the evolution of calcified tissues in vertebrates, we initiated a search for lower vertebrate orthologs of SIBLING genes. In the present study, an IBSP ortholog from a reptile (caiman) and two distinct orthologs from an amphibian (African clawed toad) were identified and characterized. As expected, the toad IBSP genes were transcribed only in calcified tissue (jaw and tibia), as also seen in mammals. The caiman, toad, avian, and mammalian IBSPs share several unique features specific for IBSP and apparently have similar properties. Furthermore, analysis of the sequences suggested that the IBSP molecule might have gradually intensified its functions related to calcification during its evolutionary process through tetrapods.
Asunto(s)
Caimanes y Cocodrilos/genética , ADN/genética , Factores de Iniciación de Péptidos/genética , Sialoglicoproteínas/genética , Xenopus laevis/genética , Secuencia de Aminoácidos , Animales , Secuencia de Bases , Clonación Molecular , Cartilla de ADN , ADN Complementario/genética , Humanos , Sialoproteína de Unión a Integrina , Mamíferos/genética , Datos de Secuencia Molecular , Filogenia , Reacción en Cadena de la Polimerasa , Biosíntesis de Proteínas , ARN/genéticaRESUMEN
Development of the endocardium in the heart of 4 to 4·1/2-day-incubated chick embryos was observed light and electron microscopically, and these results were evaluated by immunohistochemistry for desmin, FLK1 (VEGFR-2) or CD31, and by in situ hybridization assays for flk1-mRNA expression. At this developmental stage, the atrium and the ventricle were already discriminated by formation of the atrio-ventricular junction. The cardiac wall consisted of three layers; the inner endocardium, the middle myocardium, and the outer epicardium. The developing endocardium was seen as a chain of single-layered endocardial cells. Along its inner surface, numerous clusters of blood corpuscles were distributed, which seemed to contain some undifferentiated endocardial cells estimated from their characteristic ultrastructure and histological topography. Several blood corpuscles were in directly contact with the myocardium at the missing portions of the developing endocardial cell-chains. Differentiating endocardial cells individually showed roundish, small and large crescent, or flat in shapes. Such a prominent change of cell shapes appeared to be in parallel with their secretory activity during the transformation from the undifferentiated cells to the endocardial cells. Furthermore, immunohistochemistry for FLK1 or CD31, and in situ hybridization assays for flk1-mRNA labeled the cells composing developing endocardial cell-chains. Though these expressional analyses could not document clearly the transition of precursor cells into endocardial cells, the present study provided for the first time some important information regarding the morphological transition process toward endocardial cells at ultrastructural levels. Anat Rec, 299:1080-1089, 2016. © 2016 Wiley Periodicals, Inc.
Asunto(s)
Endocardio/ultraestructura , Regulación del Desarrollo de la Expresión Génica , Corazón/anatomía & histología , Corazón/embriología , Microscopía Electrónica/métodos , Animales , Embrión de Pollo , Endocardio/embriología , Técnicas para Inmunoenzimas , Receptor 2 de Factores de Crecimiento Endotelial Vascular/metabolismoRESUMEN
The mangrove killifish Rivulus marmoratus, a neotropical fish in the order Cyprinodontiformes, is the only known obligatorily selfing, synchronous hermaphroditic vertebrate. To shed light on its population structure and the origin of hermaphroditism, major histocompatibility complex (Mhc) class I genes of the killifish from seven different localities in Florida, Belize, and the Bahamas were cloned and sequenced. Thirteen loci and their alleles were identified and classified into eight groups. The loci apparently arose approximately 20 million years ago (MYA) by gene duplications from a single common progenitor in the ancestors of R. marmoratus and its closest relatives. Distinct loci were found to be restricted to different populations and different individuals in the same population. Up to 44% of the fish were heterozygotes at Mhc loci, as compared to near homozygosity at non-Mhc loci. Large genetic distances between some of the Mhc alleles revealed the presence of ancestral allelic lineages. Computer simulation designed to explain these findings indicated that selfing is incomplete in R. marmoratus populations, that Mhc allelic lineages must have diverged before the onset of selfing, and that the hermaphroditism arose in a population containing multiple ancestral Mhc lineages. A model is proposed in which hermaphroditism arose stage-wise by mutations, each of which spread through the entire population and was fixed independently in the emerging clones.
Asunto(s)
Fundulidae/genética , Fundulidae/inmunología , Genes MHC Clase I , Organismos Hermafroditas , Procesos de Determinación del Sexo/genética , Procesos de Determinación del Sexo/inmunología , Alelos , Secuencia de Aminoácidos , Animales , Bahamas , Secuencia de Bases , Belice , Clonación Molecular , Simulación por Computador , ADN Complementario/genética , Evolución Molecular , Femenino , Florida , Haplotipos , Heterocigoto , Homocigoto , Masculino , Modelos Genéticos , Datos de Secuencia Molecular , Mutación , Homología de Secuencia de Ácido NucleicoRESUMEN
Ameloblastin (AMBN) is one of the enamel sheath proteins which presumably has a role in determining the prismatic structure of growing enamel crystals. There may therefore be a relationship between the molecular evolution of the AMBN gene and the development of enamel prismatic structures. To investigate whether such a relationship exists, it was necessary to identify the homologues of the AMBN gene in a reptile whose teeth lack an enamel prismatic structure. To this end, several clones containing AMBN cDNA were isolated from caiman jaws using the reverse transcription-polymerase chain reaction (RT-PCR) method. Sequence analysis of the AMBN cDNA revealed an open reading frame of 1221 bp encoding a 407-amino-acid protein. Translation of the caiman cDNA starts at the methionine corresponding to the second of two putative start codons conserved in mammalian AMBN genes. The N-terminal part of the caiman AMBN shows high amino acid sequence similarities to human, pig, cattle, rat and mouse AMBN sequences, as well as several other features that have been conserved throughout the evolution of reptiles and mammals. Unexpectedly, the nucleotide sequences of the 3' untranslated region (UTR) are also conserved, not only within mammalian genes but also between reptilian and mammalian genes. The caiman AMBN gene is a single-copy gene, transcribed only in the jaws, presumably in teeth.
Asunto(s)
Caimanes y Cocodrilos/genética , Proteínas del Esmalte Dental/genética , Secuencia de Aminoácidos , Animales , Secuencia de Bases , ADN/química , ADN/genética , ADN Complementario/química , ADN Complementario/genética , Exones , Expresión Génica , Genes/genética , Intrones , Datos de Secuencia Molecular , Filogenia , Alineación de Secuencia , Análisis de Secuencia de ADN , Homología de Secuencia de Aminoácido , Homología de Secuencia de Ácido NucleicoRESUMEN
The macrophage migration inhibitory factor (MIF) is a cytokine produced by T lymphocytes and macrophages in response to inflammatory stimuli. We sequenced MIF cDNA clones of two jawless fishes, the sea lamprey (Petromyzon marinus) and the North Atlantic hagfish (Myxine glutinosa), as well as of the jawed (cichlid) fish Paralabidochromis chilotes. The fish MIF-encoding genes have the same exon-intron organization as the mammalian MIF genes and are present in one copy per haploid genome. Secondary and tertiary structure predictions suggest that the fish MIF proteins have a topology characteristic of the entire MIF-family of proteins. Phylogenetic analysis separates the known nematode members of the family into two groups, one having a sister group relationship with the mammalian D-dopachrome tautomerase (DDT) proteins and the other being related to vertebrate MIFs. It also reveals a high degree of convergent evolution among the members of the family. Finally, it suggests that the divergence of MIF and DDT occurred before the emergence of nematodes in metazoan evolution.
Asunto(s)
Cíclidos/clasificación , Evolución Molecular , Anguila Babosa/clasificación , Lampreas/clasificación , Factores Inhibidores de la Migración de Macrófagos/clasificación , Secuencia de Aminoácidos , Animales , Secuencia de Bases , Cíclidos/genética , Anguila Babosa/genética , Lampreas/genética , Factores Inhibidores de la Migración de Macrófagos/genética , Datos de Secuencia Molecular , Filogenia , Alineación de SecuenciaRESUMEN
Zinc (Zn)-deficiency causes a reduction in food intake and alters adipose metabolism. The effect of zinc restriction in rats on the selection of fish-oil and lard was studied during a period of reduced appetite. The reduction of appetite was caused by an experimentally induced Zn-deficiency. Four-week-old male rats were divided into three dietary treatment groups: Zn-adequate (ZnA, 30.9 mg Zn/kg), marginal Zn-deficient (ZnM, 5.9 mg Zn/kg) or Zn-deficient (ZnD, 0.9 mg Zn/kg). The three groups were placed on a self-selection regimen of the ZnA-fish-oil diet (ZnA-FD) and the ZnA-lard diet (ZnA-LD), the ZnM-FD and the ZnM-LD or the ZnD-FD and the ZnD-LD, respectively for 24 d. The amount of the FD intake in the ZnD group decreased to 0.5 g/d after day 4-6 of self-selecting on the LD and the FD and no significant increase in the FD intake in the group was observed during the self-selection period. However, after day 7-9 and 13-15, the FD intake of the ZnA and the ZnM groups increased, respectively, and at the end of the self-selection period the ZnM and the ZnA rats consumed about 2.0 g FD/d and 4.5 g FD/d, respectively. The FD intake ratio [FD intake (g)/total intake (g)] in the ZnD rats during the self-selection period was the lowest and that in the ZnA rats was the highest of three groups. In conclusion, we showed that zinc status alters fish-oil and lard selection patterns and ZnD rats did not show a preference for fish-oil.
Asunto(s)
Apetito , Grasas de la Dieta , Ingestión de Energía , Aceites de Pescado , Preferencias Alimentarias , Zinc/deficiencia , Animales , Dieta , Masculino , Ratas , Ratas EndogámicasRESUMEN
To investigate the causes why pups of dams fed a low-fat high-carbohydrate diet (LFD) showed a strong preference for fat, three groups of dams were fed one of three diets during pregnancy and lactation: the LFD, a control diet (CTD) or a high-fat low-carbohydrate diet (HFD). After weaning, pups of each of the three groups were divided into two equal subgroups (Pair 1 and Pair 2), for a total of six pup subgroups. Each subgroup was placed on a two-choice diet program of the LFD and the HFD (Pair 1), or the LFD and a HFDLE (with cellulose added to maintain the same energy concentration as the LFD) (Pair 2), for 3 wk. Although the energy intake of dams fed the LFD during the nursing period was lower than that of the HFD group, no significant difference in body weight was observed among the three groups. At weaning, the body weight of pups nursed by dams fed the LFD was lower than that of the other groups. In Pair 1, the HFD intake ratio of the LFD and the HFD groups during the self-selection period was higher than that of the CTD group. In Pair 2, the HFDLE intake ratio of the LFD and the CTD groups was lower than that of the HFD group. At the end of the self-selection period, no significant difference in body weight was observed among the three groups of Pair 1. However, in Pair 2, the body weight of the LFD group was lower than that of the other groups. Therefore, it was supposed that pups of dams fed the LFD showed strong preference for the HFD containing high energy in order to achieve optimal growth.
Asunto(s)
Dieta con Restricción de Grasas/efectos adversos , Dieta Alta en Grasa , Preferencias Alimentarias , Lactancia , Fenómenos Fisiologicos Nutricionales Maternos , Adiposidad , Animales , Conducta Animal , Ingestión de Energía , Femenino , Hiperinsulinismo/sangre , Hiperinsulinismo/etiología , Insulina/sangre , Masculino , Embarazo , Ratas , Ratas Sprague-Dawley , Destete , Aumento de PesoRESUMEN
These studies aimed to compare the effects of alpha-linolenic acid (ALA)+eicosapentaenoic acid (EPA)+docosahexaenoic acid (DHA) on plasma-lipid concentrations and preferential fat intake of rats fed a lard diet (LD). Each of 2 groups of 4-wk-old male rats was used in studies 1 and 2. In studies 1 and 2, two groups of rats received the LD (LD group) and the fish-oil diet (FD; FD group), and the LD and the perilla-oil diet (PD; PD group), respectively (dietary treatment period). After 6 wk, 6 rats per group were sacrificed. The remaining rats in studies 1 and 2 were placed on a self-selection regimen of the LD and the FD, and the LD and the PD, respectively, for 3 wk (self-selection period). After the dietary treatment period, plasma lipid concentrations in the FD group were lower than those in the LD group. However, no significant difference in the concentrations was observed between the LD group and the PD group. At the beginning of the self-selection period, the ratio of the FD intake of the LD group was higher than that of the FD group. As the the ratio of the LD group decreased and that of the FD group increased no significant difference in the ratio was observed after the 9th day during the self-selection period. No significant difference in the ratio of the PD intake was observed between the LD group and the PD group during the self-selection period. Thus, although the FD decreased plasma lipid concentration and increased the preferential FD intake of the LD group at the beginning of the self-selection period, the PD did not. Our studies clearly show that dietary EPA+DHA and ALA have different physiologic effects.
Asunto(s)
Grasas de la Dieta/farmacología , Ácidos Grasos Omega-3/farmacología , Preferencias Alimentarias , Lípidos/sangre , Ácido alfa-Linolénico/farmacología , Animales , Dieta , Grasas de la Dieta/administración & dosificación , Ácidos Docosahexaenoicos/farmacología , Ácido Eicosapentaenoico/farmacología , Ácidos Grasos Omega-3/administración & dosificación , Masculino , Perilla/química , Aceites de Plantas/administración & dosificación , Aceites de Plantas/farmacología , Ratas , Ratas Endogámicas F344 , Semillas , Ácido alfa-Linolénico/administración & dosificaciónRESUMEN
The acronym Mhc, major histocompatibility complex, is customarily not allied with topics in evolutionary biology. Here, however, we attempt to demonstrate that the Mhc has much to offer to this discipline and intimate that evolutionary biologists who ignore its contributions miss out on a chance of applying a new approach to vexing questions. One aspect of the Mhc in particular affords a fresh look at the population processes that transform one species into another: the trans-species polymorphism, the passage of allelic lineages from ancestral to descendant species. We provide examples of using the Mhc polymorphism in estimating the size of the founding population of new species, and of analyzing the long-term population demographies of phylogenetic lineages. We then extend the concept of trans-species polymorphism to other genes, even those not evolving under balancing selection, and argue that the phenomenon is widespread between closely related species. On the example of the cichlid fishes of Lake Victoria, we demonstrate how the concept changes the interpretation of this so-called "species flock." We contend that the conclusions reached regarding the cichlid fishes apply also to other examples of adaptive radiation, for example that of Darwin's finches, and so provide new insights into the nature of speciation in general.
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Evolución Biológica , Inmunogenética , Complejo Mayor de Histocompatibilidad/genética , Complejo Mayor de Histocompatibilidad/inmunología , Animales , Especificidad de la EspecieRESUMEN
The haplochromine cichlid fishes of Lake Victoria (LV), East Africa, are a textbook example of adaptive radiation-a rapid divergence of multiple morphologically distinguishable forms from a few founding lineages. The forms are generally believed to constitute a "flock" of several hundred reproductively isolated species in a dozen or so genera. This belief has, until now, not been subjected to a test, however. Here, we compare genetic variation at 11 loci in 10 haplochromine populations of 6 different species. Although the genetic diversity in the populations is quite high, using a variety of statistical tests, we find no evidence of genetic differentiation among the populations of LV haplochromines. On genetic distance trees, populations of the same species intermingle with those of different species. At the molecular level, the species are indistinguishable from one another. Genetic comparisons with closely related species in 2 crater lakes indicate that the species within LV continue exchanging genes. These observations have important implications for phylogenetic reconstruction. The approach used in this study is applicable to other instances of adaptive radiation.
Asunto(s)
Cíclidos/genética , Flujo Génico , Filogenia , África Oriental , Animales , Núcleo Celular/genética , Cíclidos/clasificación , ADN Mitocondrial/química , ADN Mitocondrial/genética , Agua Dulce , Especiación Genética , Variación Genética , Modelos Genéticos , Datos de Secuencia Molecular , Análisis de Secuencia de ADN , Factores de TiempoRESUMEN
In terms of number of species, perciform (perch-like) fishes are one of the most diversified groups of modern vertebrates. Within this group, the family Cichlidae is best known for its spectacular adaptive radiation in the great lakes of East Africa. The molecular tool kit used in the study of this radiation includes the major histocompatibility complex (Mhc) genes. To refine this tool, information about the organization of the Mhc regions is badly needed. In this study, the first step was taken toward providing such information for the Mhc class one regions of Oreochromis niloticus, a representative species of the tilapiine branch of the Cichlidae, for which good bacterial artificial chromosome library is available. Screening of the library with class I gene probes led to the identification and isolation of 31 class-I-positive clones. Sequencing of one of these clones and partial characterization of the remaining clones for the presence of class I exons resulted in the construction of two contigs representing the class I region of this species as well as identification of seven additional class-I-positive singleton clones. The O. niloticus genome was shown to contain at least 28 class I genes or gene fragments. The shorter of the two contigs was approximately 330 kb long and contained eight class I genes/gene fragments; the longer contig encompassed 1,200 kb of sequence and contained minimally 17 class I genes/gene fragments; three additional class I genes were found to be borne by a clone that might be part of the shorter contig.
Asunto(s)
Cíclidos/inmunología , Genes MHC Clase I , Animales , Secuencia de Bases , Cromosomas Artificiales Bacterianos/genética , Cíclidos/genética , Expresión Génica , Antígenos de Histocompatibilidad Clase I/clasificación , Antígenos de Histocompatibilidad Clase I/genética , Datos de Secuencia Molecular , Filogenia , Análisis de Secuencia de ADNRESUMEN
CD45 of jawed vertebrates is a receptor-type protein tyrosine phosphatase regulating lymphocyte development and activation. To shed light on the evolution of the CD45 gene, the organization of its orthologue in the lamprey, a jawless vertebrate, was determined. Compared to its mammalian and fugu counterparts, the lamprey gene was found to be lacking several exons in the segment encoding the extracellular part of the protein. In consequence, this part contains only one instead of the two or three fibronectin type III domains typical of the mammalian molecules. The lamprey transcripts of the CD45 gene occur in several variants originating by alternative splicing, including some not observed previously in other vertebrates. Most remarkable of these are splice variants generated by the use of intra-exonic splicing signals and thus lacking one half, one third, or two thirds of an exon and yet apparently translated in the correct reading frame. The lamprey gene contains polymorphic sites not only in the segment encoding the extracellular portion but also in the segment specifying the cytoplasmic part of the molecule. Polymorphism is generated by both mutations and recombination. Some of the alleles may have persisted long enough to represent transspecies polymorphism presumably maintained by positive selection. Phylogenetic analysis suggests that ancestors of the CD45 gene may have existed before the divergence of coelomate from pseudocoelomate metazoans.
Asunto(s)
Empalme Alternativo , Lampreas/genética , Antígenos Comunes de Leucocito/genética , Polimorfismo Genético , Animales , Secuencia de Bases , Southern Blotting , Glicosilación , Datos de Secuencia Molecular , Filogenia , Regiones Promotoras GenéticasRESUMEN
An expressed sequence tag with significant similarity to a vertebrate T-cell receptor (Tcr) sequence was found in a cDNA library prepared from the posterior part of the adult amphioxus, Branchiostoma lanceolatum ( Brla). Characterization of the corresponding cDNA clone revealed the presence of an open reading frame encoding a 351 amino acid residue-long polypeptide. The putative protein, tentatively designated Brla-VDB for "V-domain bearing", appears to consist of two domains. The N-terminal domain begins with a putative leader peptide followed by a sequence resembling the V domain of the CTX protein originally found to be expressed in the cortical thymocytes of the clawed frog Xenopus. The C-terminal domain of the VDB protein does not show significant sequence similarity to any entry in the databases and contains five hydrophobic segments separated by short intervening hydrophilic stretches. It may therefore belong to a protein that crosses the plasma membrane five times. These findings support the notion that V domains resembling those found in Tcrs evolved in nonvertebrates before the emergence of the adaptive immune system and may have participated in functions not involved directly in immunity.
Asunto(s)
Cordados no Vertebrados/inmunología , Región Variable de Inmunoglobulina/genética , Proteínas de Xenopus , Secuencia de Aminoácidos , Animales , Antígenos de Diferenciación de Linfocitos T , Secuencia de Bases , Cordados no Vertebrados/genética , Cordados no Vertebrados/metabolismo , Región Variable de Inmunoglobulina/inmunología , Proteínas de la Membrana/genética , Proteínas de la Membrana/metabolismo , Datos de Secuencia Molecular , Alineación de SecuenciaRESUMEN
Mammalian natural killer (NK) cells are cytotoxic lymphocytes that express receptors specific for MHC class I molecules. The NK cell receptors belong to two structurally unrelated families, the killer cell Ig-like receptors and the killer cell C-type lectin receptors. We describe a cDNA clone derived from the bony (cichlid) fish Paralabidochromis chilotes and show that it encodes a protein related to the CD94/NK cell group 2 (NKG2) subfamily of the killer cell C-type lectin receptors. The gene encoding this receptor in a related species, Oreochromis niloticus, has a similar structure to the human CD94/NKG2 genes and is a member of a multigene cluster that resembles the mammalian NK cell gene complex. Thus, the CD94/NKG2 subfamily of NK cell receptors must have arisen before the divergence of fish and tetrapods and may have retained its function (possibly monitoring the expression of MHC class I molecules) for >400 million years.