Evolution of the entire arthropod Hox gene set predated the origin and radiation of the onychophoran/arthropod clade.

BACKGROUND: Dramatic changes in body size and pattern occurred during the radiation of many taxa in the Cambrian, and these changes are best documented for the arthropods. The sudden appearance of such diverse body plans raises the fundamental question of when the genes and the developmental control systems that regulate these designs evolved. As Hox genes regulate arthropod body patterns, the evolution of these genes may have played a role in the origin and diversification of the arthropod body plan from a homonomous ancestor. To trace the origin of arthropod Hox genes, we examined their distribution in a myriapod and in the Onychophora, a sister group to the arthropods. RESULTS: Despite the limited segmental diversity within myriapods and Onychophora, all insect Hox genes are present in both taxa, including the trunk Hox genes Ultrabithorax and abdominal-A as well as an ortholog of the fushi tarazu gene. Comparative analysis of Hox gene deployment revealed that the anterior boundary of expression of trunk Hox genes has shifted dramatically along the anteroposterior axis between Onychophora and different arthropod classes. Furthermore, we found that repression of expression of the Hox target gene Distal-less is unique to the insect lineage. CONCLUSIONS: A complete arthropod Hox gene family existed in the ancestor of the onychophoran/arthropod clade. No new Hox genes were therefore required to catalyze the arthropod radiation; instead, arthropod body-plan diversity arose through changes in the regulation of Hox genes and their downstream targets.

Enhanced antiopiate activity and enzyme resistance in peptidomimetics of FMRFamide containing (E)-2,3-methanomethionine.

FMRFamide is a molluscan peptide that has shown antiopiate activity in a number of mammalian test systems. The current study determined the antiopiate potency of FMRFamide and two conformationally constrained peptidomimetics of FMRFamide containing stereoisomers of (E)-2,3-methanomethionine. Morphine abstinence signs were observed after varying doses (0.25-25.0 microgram) of these substances were injected into the third ventricle of morphine-dependent rats. Both peptidomimetics were far more potent than FMRFamide itself. In addition, although both peptidomimetics bound with lower affinity than FMRFamide to rat spinal cord receptors for NPFF (the mammalian FMRFamide-like peptide), they were far more resistant than FMRFamide to enzymatic degradation by leucine aminopeptidase.

Evidence for at least three transcribed BoLA class I loci.

Serological data identify a single major histocompatibility complex (MHC) class I locus in cattle. Molecular data, however, demonstrate the presence of at least two cattle MHC (BoLA) class I loci. To investigate the number of transcribed BoLA class I genes, we amplified cattle cDNA by using a single MHC class I-specific primer that hybridized to a conserved region of exon 4 and a non-specific 3' primer. Six BoLA class I cDNAs have been cloned and sequenced from a Bos taurus bull heterozygous for BoLA class I serological antigens, demonstrating the presence of a minimum of three loci. Sequence comparisons suggested that one of these cDNAs may be an unexpressed allele or the product of a nonclassical locus.

Guanine uptake and metabolism in Neurospora crassa.

Guanine is transported into germinated conidia of Neurospora crassa by the general purine base transport system. Guanine uptake is inhibited by adenine and hypoxanthine but not xanthine. Guanine phosphoribosyltransferase (GPRTase) activity was demonstrated in cell extracts of wild-type germinated conidia. The Km for guanine ranged from 29 to 69 micro M in GPRTase assays; the Ki for hypoxanthine was between 50 and 75 micro M. The kinetics of guanine transport differ considerably from the kinetics of GPRTase, strongly suggesting that the rate-limiting step in guanine accumulation in conidia is not that catalyzed by GPRTase. Efflux of guanine or its metabolites appears to have little importance in the regulation of pools of guanine or guanine nucleotides since very small amounts of 14C label were excreted from wild-type conidia preloaded with [8-14C]guanine. In contrast, excretion of purine bases, hypoxanthine, xanthine, and uric acid appears to be a mechanism for regulation of adenine nucleotide pools (Sabina et al., Mol. Gen. Genet. 173:31-38, 1979). No label from exogenous [8-14C]guanine was ever found in any adenine nucleotides, nucleosides, or the base, adenine, upon high-performance liquid chromatography analysis of acid extracts from germinated conidia of wild-type of xdh-l strains. The 14C label from exogenous [8-14C]guanine was found in GMP, GDP, GTP, and the GDP sugars as well as in XMP. Xanthine and uric acid were also labeled in wild-type extracts. Similar results were obtained with xdh-l extracts except that uric acid was not present. The labeled xanthine and XMP strongly suggest the presence of guanase and xanthine phosphoribosyltransferase in germinated conidia.

Unusually limited nucleotide sequence variation of the expressed major histocompatibility complex class I genes of a New World primate species (Saguinus oedipus).

Although major histocompatibility complex (MHC) class I molecules are, as a rule, highly polymorphic in mammalian species, those of the New World primate Saguinus oedipus (cotton-top tamarin) exhibit limited polymorphism. We have cloned and sequenced twelve MHC class I cDNAs from this species. Since cloned cotton-top tamarin cell lines express three to six MHC class I molecules, this species must have at least three functional MHC class I loci. There was, however, no evidence of locus-specific substitutions in the tamarin cDNAs. Unlike all other species studied, tamarin MHC class I cDNAs displayed limited nucleotide sequence variation. The sequence similarity between the two most divergent tamarin cDNAs was 95%. To ensure that the polymerase chain reaction (PCR) primers employed in these studies had amplified all of the tamarins' expressed MHC class I genes, we used another set of primers to amplify only exons 2 and 3 from RNA and DNA. PCR of genomic DNA resulted in the amplification of six distinct clones, of which only three were well expressed. Two of these nonexpressed genes were pseudogenes and the other was a nonclassical gene. Southern blot analysis demonstrated that the tamarin has 8-11 MHC class I genes, suggesting we had indeed cloned the majority of these genes. Cotton-top tamarins are, therefore, unique among mammalian species studied to date in that they express MHC class I molecules with limited nucleotide sequence variation.

Segmental exchange between MHC class I genes in a higher primate: recombination in the gorilla between the ancestor of a human non-functional gene and an A locus gene.

Classical human major histocompatibility complex (MHC) class I molecules are the products of highly diverse gene loci. It has been suggested that segmental exchange may play a role in the generation of diversity at the antigen recognition site of MHC class I molecules. Here we present the cloning, sequencing and expression of two gorilla A locus cDNAs. One of these cDNAs shows remarkable similarity to the non-functional HLA-AR locus gene (5.4-LBF) only in exon 2. The remainder of the cDNA, however, is most closely related to other classical higher primate A locus genes. This suggests that a segmental exchange may have occurred between the ancestor of the non-functional HLA-AR gene and a classical gorilla A locus gene. Furthermore, the recombination event resulting in Gogo-A3 has affected its antigen recognition site. These data, therefore, demonstrate that segmental exchange can generate diversity at the antigen recognition sites of primate MHC class I molecules and suggest that non-functional genes can contribute to the generation of diversity of classical MHC class I genes.

Sequence and evolution of cattle MHC class I cDNAs: concerted evolution has not taken place in cattle.

To explore genetic mechanisms responsible for major histocompatibility complex (MHC) class I evolution in the artiodactyls, we cloned and sequenced MHC class I cDNAs from a Bos taurus bull heterozygous for cattle MHC (BoLA) class I serological specificities w2 and w30. Four unique cDNAs were found, indicating the presence of at least two MHC class I loci. Analysis of these four cDNAs and all previously published BoLA cDNA sequences suggested that there may be three cattle MHC class I loci. Additionally, comparison of all of the BoLA class I cDNAs to MHC class I cDNAs of other artiodactyls showed that some of the BoLA class I cDNAs were more similar to certain sheep cDNAs than they were to other cattle cDNAs. These data indicate that each BoLA class I locus has evolved independently after an ancestral gene duplication event and that inter-locus segmental exchange or concerted evolution has not occurred rapidly enough to cause extensive divergence between the orthologous MHC class I loci of sheep and cattle.

Chimpanzee MHC class I A locus alleles are related to only one of the six families of human A locus alleles.

There are nearly 50 alleles at the highly polymorphic HLA-A class I locus that fall into six distinct families. To determine the allelic repertoire and the mechanism of generation of diversity of the A locus in primates we have analyzed A locus alleles from 28 apparently unrelated chimpanzees (Pan troglodytes) and bonobos (Pan paniscus). We have, therefore, compared the sequences of 19 HLA-A homologues from chimpanzees and bonobos to 42 HLA-A sequences. HLA-A homologues were well preserved in chimpanzees and bonobos with very few new substitutions present in the A locus alleles of both species of chimpanzee. Surprisingly, all chimpanzees and bonobos expressed A locus alleles related to only one of the six families of human HLA-A alleles. This suggests that the common ancestor of these two species either passed through a genetic bottleneck or that selection has favored the maintenance of the HLA-A1, -A3, -A11 family in chimpanzees.

A uniquely high level of recombination at the HLA-B locus.

Major histocompatibility complex (MHC) loci are some of the most polymorphic genes in the animal kingdom. Recently, it has been suggested that although most of the human MHC loci are relatively stable, the HLA-B locus can undergo rapid changes, especially in isolated populations. To investigate the mechanisms of HLA-B evolution we have compared the sequences of 19 HLA-B homologues from chimpanzees and bonobos to 65 HLA-B sequences. Analysis of the chimpanzee and bonobo HLA-B homologues revealed that despite obvious similarities between chimpanzee and human alleles in exon 2, there was little conservation of exon 3 between humans and the two chimpanzee species. This finding suggests that, unlike all other HLA loci, recombination has characterized the HLA-B locus and its homologues for over 5 million years.

HLA-B alleles of the Navajo: no evidence for rapid evolution in the Nadene.

New HLA-B locus alleles have been found in South American Amerindian populations but were largely absent in North American Amerindian tribes also descended from this first Paleo-Indian migration. We have now extended these studies to the Navajo, descendants of the second Nadene migration. No new functional alleles were found at the B locus of this tribe. This limited study supports the notion that while new B locus variants are common in South American Amerindians, it is more difficult to find new B locus alleles in North American native peoples. Whether this dichotomy is due to differences in pathogen environment and/or population structures between North and South America remains a subject of speculation.

HLA-B alleles of the Cayapa of Ecuador: new B39 and B15 alleles.

Recent data suggest that HLA-B locus alleles can evolve quickly in native South American populations. To investigate further this phenomenon of new HLA-B variants among Amerindians, we studied samples from another South American tribe, the Cayapa from Ecuador. We selected individuals for HLA-B molecular typing based upon their HLA class II typing results. Three new variants of HLA-B39 and one new variant of HLA-B15 were found in the Cayapa: HLA-B*3905, HLA-B*3906, HLA-B*3907, and HLA-B*1522. A total of thirteen new HLA-B alleles have now been found in the four South American tribes studied. Each of these four tribes studied, including the Cayapa, had novel alleles that were not found in any of the other tribes, suggesting that many of these new HLA-B alleles may have evolved since the Paleo-Indians originally populated South America. Each of these 13 new alleles contained predicted amino acid replacements that were located in the peptide binding site. These amino acid replacements may affect the sequence motif of the bound peptides, suggesting that these new alleles have been maintained by selection. New allelic variants have been found for all common HLA-B locus antigenic groups present in South American tribes with the exception of B48. In spite of its high frequency in South American tribes, no evidence for variants of B48 has been found in all the Amerindians studied, suggesting that B48 may have unique characteristics among the B locus alleles.

New recombinant HLA-B alleles in a tribe of South American Amerindians indicate rapid evolution of MHC class I loci.

Evidence suggests that the New World was colonized only 11,000-40,000 years ago by Palaeo-Indians. The descendants of these Palaeo-Indians therefore provide a unique opportunity to study the effects of selection on major histocompatibility complex class I genes over a short period. Here we analyse the class I alleles of the Waorani of South America and the Zuni of North America. Four of the Waorani HLA-B alleles were new functional variants which could be accounted for by intralocus recombination. In contrast, all of the Zuni HLA-A and -B molecules were present in caucasians and orientals. This suggests that the new Waorani HLA-B variants arose in South America. The description of four new HLA-B alleles in the Waorani and another five new HLA-B alleles from two other tribes of South American Amerindians indicates that the HLA-B locus can evolve rapidly in isolated populations. These studies underline the importance of gathering genetic data on endangered native human populations.