RESUMEN
An approach designed to map and generate mutations in the region of the short arm of the mouse Y chromosome, known to be involved in sex determination and spermatogenesis, is described. This relies on homologous Yp-Sxra pairing and asymmetrical exchange which can occur at meiosis in XY males carrying Sxra on their X chromosome. Such exchange potentially generates deficiencies and duplications of Yp or Sxra. Three fertile XY females were found out of about 450 XY offspring from XSxra/Y x XX crosses. In all three, despite evidence for deletion of Y chromosomal material, the Sry locus was intact. Each deletion involved a repeat sequence, Sx1, located at a distance from Sry. Since expression of Sry was affected these results suggest that long range position effects have disrupted Sry action.
Asunto(s)
Deleción Cromosómica , Trastornos del Desarrollo Sexual , Proteínas Nucleares , Factores de Transcripción , Cromosoma X , Cromosoma Y , Animales , Secuencia de Bases , Cartilla de ADN , Proteínas de Unión al ADN/genética , Femenino , Masculino , Ratones , Ratones Endogámicos , Datos de Secuencia Molecular , Diferenciación Sexual/genética , Proteína de la Región Y Determinante del SexoRESUMEN
In many reptile species, gonadal sex is affected by environmental temperature during a critical period of embryonic development-a process known as temperature-dependent sex determination (TSD).1 The oviparous red-eared slider turtle, Trachemys scripta, has a warm-female/cool-male TSD system and is among the best-studied members of this group.2 When incubated at low temperatures, the somatic cells of the bipotential gonad differentiate into Sertoli cells, the support cells of the testis, whereas at high temperatures, they differentiate into granulosa cells, the support cells of the ovary.3 Here, we report the unexpected finding that temperature independently affects the number of primordial germ cells (GCs) in the embryonic gonad at a time before somatic cell differentiation has initiated. Specifically, embryos incubated at higher, female-inducing temperatures have more GCs than those incubated at the male-inducing temperature. Furthermore, elimination of GCs in embryos incubating at intermediate temperatures results in a strong shift toward male-biased sex ratios. This is the first evidence that temperature affects GC number and the first evidence that GC number influences sex determination in amniotes. This observation has two important implications. First, it supports a new model in which temperature can impact sex determination in incremental ways through multiple cell types. Second, the findings have important implications for a major unresolved question in the fields of ecology and evolutionary biology-the adaptive significance of TSD. We suggest that linking high GC number with female development improves female reproductive potential and provides an adaptive advantage for TSD.
Asunto(s)
Tortugas , Animales , Humanos , Femenino , Masculino , Temperatura , Feminización , Células Germinativas , Recuento de Células , Procesos de Determinación del Sexo , Diferenciación SexualRESUMEN
BACKGROUND: The gene Sry acts as a developmental switch, initiating a pathway of gene activity that leads to the differentiation of testis rather than ovary from the indifferent gonad (genital ridge) in mammalian embryos. The early events following Sry expression include rapid changes in the topographical organization of cells in the XY gonad. To investigate the contribution of mesonephric cells to this process, gonads from wild-type mice (CD1), and mesonephroi from a transgenic strain ubiquitously expressing beta-galactosidase (ROSA26), were grafted together in vitro. After culture, organs were fixed and stained for beta-galactosidase activity to identify cells contributed from the mesonephros to the male or female gonad. RESULTS: Migration of mesonephric cells occurred into XY but not XX gonads from 11.5-16.5 days post coitum (dpc). Somatic cells contributed from the mesonephros were distinguished by their histological location and by available cell-specific markers. Some of the migrating cells were endothelial; a second population occupied positions circumscribing areas of condensing Sertoli cells; and a third population lay in close apposition to endothelial cells. CONCLUSIONS: OFFgration from the mesonephros to the gonad is male specific at this stage of development and depends on an active signal that requires the presence of a Y chromosome in the gonad. The signals that trigger migration operate over considerable distances and behave as chemoattractants. We suggest that migration of cells into the bipotential gonad may have a critical role in initiating the divergence of development towards the testis pathway.
Asunto(s)
Movimiento Celular , Gónadas/embriología , Proteínas Nucleares , Transducción de Señal , Factores de Transcripción , Animales , División Celular , Factores Quimiotácticos/metabolismo , Proteínas de Unión al ADN/metabolismo , Femenino , Gónadas/citología , Masculino , Ratones , Ratones Endogámicos C57BL , Técnicas de Cultivo de Órganos , Caracteres Sexuales , Proteína de la Región Y Determinante del Sexo , Factores de TiempoRESUMEN
The sex determining gene, Sry, determines the sex of the organism by initiating development of a testis rather than an ovary from the cells of the bipotential gonad. In the 10 years since the discovery of Sry, new genes and cellular pathways that operate in the establishment of the gonadal primordium and the initiation of testis development have been discovered. Experiments defining mechanisms downstream of Sry are providing clear examples of how a regulatory transcription factor initiates cellular processes including proliferation and cell migration, which in turn influence architectural patterning, fate commitment, and differentiation of cells within an organ.
Asunto(s)
Proteínas de Unión al ADN/fisiología , Proteínas Nucleares , Ovario/embriología , Procesos de Determinación del Sexo , Testículo/embriología , Factores de Transcripción , Animales , Linaje de la Célula , Movimiento Celular , Drosophila/embriología , Femenino , Masculino , Mamíferos/embriología , Ratones , Microscopía Electrónica de Rastreo , Morfogénesis , Proteína de la Región Y Determinante del SexoRESUMEN
In mammals, the primary step in male sex determination is the initiation of testis development which depends on the expression of the Y-linked testis determining gene, Sry. The mechanisms by which Sry controls this process are unknown. Studies showed that cell migration from the adjacent mesonephros only occurs into XY gonads; however, it was not known whether this effect depended on Sry, another Y-linked gene, or the presence of one versus two X chromosomes. Here we provide genetic proof that Sry is the only Y-linked gene necessary for cell migration into the gonad. Cell migration from the mesonephros into the differentiating gonad is consistently associated with Sty's presence and with testis cord formation, suggesting that cell migration plays a critical role in the initiation of testis cord development. The induction of cell migration represents the earliest signaling pathway yet assigned to Sry.
Asunto(s)
Proteínas de Unión al ADN/genética , Regulación del Desarrollo de la Expresión Génica , Gónadas/metabolismo , Mesonefro/citología , Mesonefro/embriología , Proteínas Nucleares , Factores de Transcripción , Animales , Movimiento Celular , Proteínas de Unión al ADN/metabolismo , Inducción Embrionaria/genética , Gónadas/embriología , Masculino , Mesonefro/metabolismo , Ratones , Ratones Endogámicos , Ratones Transgénicos , Técnicas de Cultivo de Órganos , Proteína de la Región Y Determinante del Sexo , Testículo/embriología , Cromosoma YRESUMEN
Neonatal unirradiated mice of W-mutant genotypes, with a hematopoietic stem cell defect and anemia, were injected i.v. with normal fetal liver hematopoietic cells. Efficient, long-term engraftment occurred as a result of the competitive advantage to the donor stem cells. The frequency of engraftment and rate of repopulation characteristically diminish in the series W/Wv, Wf/Wf, and Wv/+, in which the severity of the endogenous defect is progressively less. H-2 compatibility is required in the inbred strain combinations examined; other histocompatibility loci play a minor role in some strain combinations. Engraftment is due to self-renewing hematopoietic stem cells ancestral to myeloid and lymphoid lineages. The more mildly defective mutants display much greater variability in the kinetics of repopulation--a result consistent with seeding by single, or very few, stem cells that form developing clones. Engraftment efficiency is reduced by prolonged culture of fetal liver cells during experimental infection by recombinant retroviruses; nevertheless, after 24 h in vitro to achieve retroviral marking, stem cells retain their ability to repopulate and develop in W/Wv neonates.
Asunto(s)
Animales Recién Nacidos/fisiología , Marcadores Genéticos , Trasplante de Células Madre Hematopoyéticas , Ratones Mutantes/fisiología , Animales , Diferenciación Celular , Supervivencia Celular , Células Cultivadas , Recuento de Eritrocitos , Células Madre Hematopoyéticas/citología , Células Madre Hematopoyéticas/fisiología , Histocompatibilidad , Recuento de Leucocitos , Hígado/citología , Trasplante de Hígado , Ratones , Ratones Endogámicos , Infecciones por Retroviridae/patologíaRESUMEN
A strain of Bacillus cereus isolated from a food poisoning outbreak characterized by vomiting has been shown to be capable of causing vomiting when cultures grown on rice, but not other media, were fed to Rhesus monkeys. In contrast, a strain isolated from a diarrhoeal outbreak produced diarrhoea, but not vomiting, when grown on various media in similar feeding trials. Furthermore, culture filtrates from the diarrhoeal strain caused fluid accumulation in ligated rabbit ileal loops whereas those from the vomiting strain did not. It is proposed that at least two enterotoxins are involved, one responsible for the vomiting and one for the diarrhoeal symptoms.
Asunto(s)
Bacillus cereus/patogenicidad , Enterotoxinas/análisis , Animales , Bioensayo , Medios de Cultivo , Diarrea/etiología , Heces/microbiología , Haplorrinos , Íleon , Oryza , Conejos , Especificidad de la Especie , Vómitos/etiologíaAsunto(s)
Mamíferos/genética , Proteínas Nucleares , Proteínas Represoras , Análisis para Determinación del Sexo , Animales , Receptor Nuclear Huérfano DAX-1 , Proteínas de Unión al ADN/genética , Femenino , Proteínas del Grupo de Alta Movilidad/genética , Humanos , Masculino , Ratones , Receptores de Ácido Retinoico/genética , Factor de Transcripción SOX9 , Proteína de la Región Y Determinante del Sexo , Factores de Transcripción/genética , Cromosoma XRESUMEN
Cell migration is one of the earliest events required for development of the testis. Migration occurs only in XY gonads downstream of Sry expression and is required for the subsequent epithelialization of testis cords. Using organ culture experiments and tissue recombination, we and others speculated that peritubular myoid (PTM) cells were among the migratory cells and were likely the cell type required for cord formation. However, because no unique marker was found for PTM cells, their positive identification during or after migration remained unclear. alpha-Smooth Muscle Actin (alphaSma; approved gene symbol Acta2), a classic marker of adult PTM cells,is expressed broadly in testis interstitial cells at E12.5, and becomes highly enriched in PTM cells by E15.5-16.5. We used a novel transgenic line expressingEYFP under the control of an alphaSma promoter to determine whether alphaSma-EYFP positive cellsmigrate into the gonad. Surprisingly, mesonephroi expressing alphaSma-EYFP do not contribute any EYFP positive cells to XY gonads when used as donors in recombination cultures. These results indicate that alphaSma-EYFP cells do not migrate into the gonad during the critical window of sex determination and cannot be the migrating cell type required for testis cord formation. Our results suggest that PTM cells, and most other interstitial lineages, with the exception of endothelial cells, are induced within the gonad. These experiments suggest that endothelial cells are the migrating cell type required for epithelialization of testis cords.
Asunto(s)
Movimiento Celular/fisiología , Mesonefro/citología , Mesonefro/embriología , Procesos de Determinación del Sexo , Cordón Espermático/embriología , Testículo/embriología , Actinas/genética , Animales , Embrión de Mamíferos , Proteínas Luminiscentes/genética , Proteínas Luminiscentes/metabolismo , Masculino , Ratones , Ratones Transgénicos , Túbulos Seminíferos/citología , Túbulos Seminíferos/embriología , Túbulos Seminíferos/metabolismo , Cordón Espermático/citología , Cordón Espermático/metabolismo , Testículo/citología , Testículo/metabolismo , Transgenes , Cromosoma X , Cromosoma YRESUMEN
Relatively little is known regarding the signals that regulate the proliferation and sex-specific development of germ cells during mammalian fetal gonad differentiation. Members of the bone morphogenetic protein (BMP) family have been identified as key regulators of germ cells in the Drosophila gonad. Here we show that in mice Bmp7 is expressed in gonads of both sexes and is required for germ cell proliferation during a narrow window of development between 10.5-11.5 days post coitum (dpc). The proliferation defect is more severe in male than in female embryos suggesting that there are sexually dimorphic compensatory pathways. BMP signaling appears to be an evolutionarily conserved pathway regulating embryonic germ cell proliferation in vertebrate and invertebrate species.
Asunto(s)
Proteínas Morfogenéticas Óseas/fisiología , Proliferación Celular , Células Germinativas/metabolismo , Gónadas/metabolismo , Factor de Crecimiento Transformador beta/fisiología , Animales , Proteína Morfogenética Ósea 7 , Proteínas Morfogenéticas Óseas/genética , Proteínas Morfogenéticas Óseas/metabolismo , Diferenciación Celular , Femenino , Feto , Regulación del Desarrollo de la Expresión Génica , Células Germinativas/citología , Gónadas/citología , Gónadas/embriología , Hematoxilina/metabolismo , Inmunohistoquímica , Hibridación in Situ , Masculino , Ratones , Ratones Mutantes , Ovario/citología , Ovario/embriología , Ovario/metabolismo , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Testículo/citología , Testículo/embriología , Testículo/metabolismo , Factor de Crecimiento Transformador beta/genética , Factor de Crecimiento Transformador beta/metabolismoRESUMEN
In mammals the male sex determination switch is controlled by a single gene on the Y chromosome, SRY. SRY encodes a protein with an HMG-like DNA-binding domain, which probably acts as a local organizer of chromatin structure. It is believed to regulate downstream genes in the sex determination cascade, although no direct targets of SRY are clearly known. More genes in the pathway have been isolated through mutation approaches in mouse and human. At least three genes, SRY itself, SOX9, and DAX1, are dosage sensitive, providing molecular evidence that the sex determination step operates at a critical threshold. SRY initiates development of a testis from the bipotential cells of the early gonad. The dimorphic male and female pathways present a rare opportunity to link a pivotal gene in development with morphogenetic mechanisms that operate to pattern an organ and the differentiation of its cells. Mechanisms of testis organogenesis triggered downstream of SRY include pathways of cell signaling controlling cell reorganization, cell proliferation, cell migration, and vascularization.
Asunto(s)
Proteínas de Unión al ADN/metabolismo , Proteínas Nucleares , Procesos de Determinación del Sexo , Factores de Transcripción , Cromosoma Y/fisiología , Secuencia de Aminoácidos , Animales , Proteínas de Unión al ADN/biosíntesis , Proteínas de Unión al ADN/genética , Femenino , Humanos , Masculino , Ratones , Datos de Secuencia Molecular , Proteína de la Región Y Determinante del Sexo , Cromosoma Y/genéticaRESUMEN
During mouse development, the gonad begins to form shortly before 10. 5 days postcoitum (dpc) on the ventromedial side of the mesonephros. The XY gonad consists of germ cells and somatic cells. The origin of the germ cells is clearly established; however, the origin of the somatic cells, especially the epithelial supporting cell lineages, called Sertoli cells, is still unclear. Sertoli cells are the first somatic cell type to differentiate in the testis and are thought to express Sry, the male sex-determining gene, and to play a crucial role in directing testis development. Previous data have suggested that the somatic cells of the gonad may arise from the mesonephric tubules, the mesonephric mesenchyme, or the coelomic epithelium. Immunohistochemical staining of the gonad at 11.5 dpc showed that the basement membrane barrier under the coelomic epithelium is discontinuous, suggesting that cells in the coelomic epithelium at this stage might move inward. To test this possibility directly, cells of the coelomic epithelium were labeled using the fluorescent lipophilic dye, DiI. We show that when labeled at tail somite 15-17 stages, corresponding to 11.2-11.4 dpc, the coelomic epithelial cells of both sexes migrated into the gonad. In XY gonads, the migrating coelomic epithelial cells became Sertoli cells, as well as interstitial cells. This ability of the coelomic epithelium to give rise to Sertoli cells was developmentally regulated. When labeled at tail somite 18-20 stages, corresponding to 11.5-11.7 dpc, the coelomic epithelial cells no longer became Sertoli cells. Instead, cells that migrated into the gonad stayed outside testis cords, in the interstitium. Migration gradually decreased and ceased by tail somite 30 stage, corresponding to 12.5 dpc, after testis cords had formed and the basement membrane layer underlying the coelomic epithelium had thickened to form the tunica albuginea. In XX gonads, coelomic epithelial cells also migrated into the gonad, but there was no obvious fate restriction during the same developmental period. Taken together, our data show that the coelomic epithelium is a source of Sertoli cells as well as other somatic cells of the gonad in the developing mouse testis.
Asunto(s)
Diferenciación Celular/fisiología , Células de Sertoli/citología , Testículo/embriología , Animales , Carbocianinas/metabolismo , Movimiento Celular/fisiología , Colorantes Fluorescentes/metabolismo , Gónadas/embriología , Gónadas/crecimiento & desarrollo , Inmunohistoquímica , Masculino , Ratones , Microscopía Fluorescente , Morfogénesis/fisiología , Somitos/citologíaRESUMEN
In mammals a single gene on the Y chromosome, Sry, controls testis formation. One of the earliest effects of Sry expression is the induction of somatic cell migration from the mesonephros into the XY gonad. Here we show that mesonephric cells are required for cord formation and male-specific gene expression in XY gonads in a stage-specific manner. Culturing XX gonads with an XY gonad at their surface, as a 'sandwich', resulted in cell migration into the XX tissue. Analysis of sandwich gonads revealed that in the presence of migrating cells, XX gonads organized cord structures and acquired male-specific gene expression patterns. From these results, we conclude that mesonephric cell migration plays a critical role in the formation of testis cords and the differentiation of XY versus XX cell types.
Asunto(s)
Proteínas de Unión al ADN/genética , Mesonefro/embriología , Proteínas Nucleares , Células de Sertoli/metabolismo , Testículo/embriología , Animales , Diferenciación Celular , Movimiento Celular , Regulación del Desarrollo de la Expresión Génica , Proteínas del Grupo de Alta Movilidad/genética , Hibridación in Situ , Laminina/metabolismo , Masculino , Ratones , Técnicas de Cultivo de Órganos , ARN Mensajero/análisis , Factor de Transcripción SOX9 , Proteína de la Región Y Determinante del Sexo , Factores de Transcripción/genética , Cromosoma Y/genéticaRESUMEN
We are interested in understanding how the field of cells which forms the gonad arises, and how the testis-determining gene, Sry, controls morphogenesis of a testis within this field of cells. To appreciate changes in the three-dimensional structure of the mouse genital ridge at this time in development, whole-mount genital ridges taken from male and female embryos over the developmental period when the initiation of testis cord morphogenesis takes place, were stained with an antibody against laminin. Samples were visualized using confocal microscopy. Anti-laminin illuminates the elaborate array of mesonephric duct and tubules which occupy the cranial two-thirds of the mesonephros at the earliest timepoint. This complex structure gradually regresses as testis cords form in male gonads. No structural organisation is recognized by this antibody in the female gonadal region during this period. Confocal sections in the Z-plane reveal continuous cellular connections between 3-6 mesonephric tubules and the gonadal primordium. These cellular bridges are present in male and female gonads, so they do not depend on the expression of Sry. We consider the possibility that these bridges constitute the pathways of the founder cells of the gonadal primordium.
Asunto(s)
Embrión de Mamíferos/citología , Gónadas/embriología , Ratones Endogámicos/embriología , Proteínas Nucleares , Análisis para Determinación del Sexo , Factores de Transcripción , Animales , Proteínas de Unión al ADN/fisiología , Femenino , Gónadas/química , Riñón/citología , Riñón/embriología , Laminina/análisis , Masculino , Ratones , Microscopía Confocal , Morfogénesis , Proteína de la Región Y Determinante del SexoRESUMEN
The use of a video recorder and the inclusion of a marker dye in material fed to rhesus monkeys has eliminated the need for the constant presence of an observer to detect an emetic response.
Asunto(s)
Toxinas Bacterianas/análisis , Bioensayo/métodos , Enterotoxinas/análisis , Vómitos , Animales , Bacillus cereus , Toxinas Bacterianas/efectos adversos , Colorantes , Enterotoxinas/efectos adversos , Haplorrinos , Macaca mulatta , Grabación de Cinta de Video , Vómitos/etiologíaRESUMEN
The proliferative longevity of totipotent hematopoietic stem cells (THSC) is a limiting factor in normal hematopoiesis and in therapy by cell- or gene-replacement, but has not yet been ascertained. We have followed the long-term fate of individual clones of mouse THSC from fetal liver or adult bone marrow, after labeling in culture, followed by engraftment and serial transplantation in unirradiated W/Wv-C57BL/6 hosts. The ancestor cell of each clone and its mitotic progeny were uniquely identifiable retrospectively by the DNA integration pattern experimentally produced by replication-incompetent recombinant murine retroviruses. These viruses provided physiologically neutral markers. The marked clones proved to be derived from THSC, based on their contributions to a wide array of myeloid and lymphoid blood lineages in the hosts. The label also identified the target cells as the population displaying clonal succession. The various labeled stem cell clones proliferated for substantially different periods of time. The longest observed clone endured, after the original cell was marked, for at least 2 1/2 years--the equivalent of a mouse's lifetime. However, the results suggest that THSC clones are not all long-lived and that even the longest-lived ones may not be potentially immortal. Thus, the unpredictable lifespan of any given THSC clone indicates the desirability of introducing multiple clones in therapeutic transplants.
Asunto(s)
Células de la Médula Ósea , Células Madre Hematopoyéticas/citología , Animales , Southern Blotting , Trasplante de Médula Ósea , División Celular , Supervivencia Celular , Ratones , Ratones Endogámicos , RetroviridaeRESUMEN
In the mouse, Sry is expressed by germ cells in the adult testis and by somatic cells in the genital ridge. Transcripts in the former exist as circular RNA molecules of 1.23 kb, which are unlikely to be efficiently translated. We have used RNase protection to map the extent of the less abundant Sry transcript in the developing gonad. We demonstrate that it is a linear mRNA derived from a single exon. This begins in the unique region 5' of the protein coding region and extends several kilobases into the 3' arm of the large inverted repeat which bounds the Sry genomic locus. Knowledge of this transcript, which is very different from that of the human SRY gene, allows us to predict its protein product and reveals several features which may be involved in translational control. Our data is also consistent with there being two promoters for the Sry gene, a proximal one that gives functional transcripts in the genital ridge and a distal promoter used in germ cells in the adult testis. As RNase protection is a quantitative technique, a detailed timecourse of Sry expression was carried out using accurately staged samples. Sry transcripts are first detectable just after 10.5 days post coitum, they reach a peak at 11.5 days and then decline sharply so that none are detected 24 hours later. This was compared with anti-Müllerian hormone gene expression, an early marker of Sertoli cells and the first known downstream gene of Sry. Amh expression begins 20 hours after the onset of Sry expression at a time when Sry transcripts are at their peak. While this result does not prove a direct interaction between the two genes, it defines the critical period during which Sry must act to initiate Sertoli cell differentiation.
Asunto(s)
Proteínas de Unión al ADN/genética , Proteínas Nucleares , Análisis para Determinación del Sexo , Espermatozoides/fisiología , Testículo/embriología , Factores de Transcripción/genética , Secuencia de Aminoácidos , Animales , Secuencia de Bases , Cartilla de ADN/genética , Expresión Génica , Técnicas Genéticas , Humanos , Masculino , Ratones , Ratones Transgénicos/genética , Datos de Secuencia Molecular , Homología de Secuencia , Proteína de la Región Y Determinante del SexoRESUMEN
Mice were repopulated with small numbers of retrovirally marked hematopoietic cells operationally definable as totipotent hematopoietic stem cells, without engraftment of cells at later stages of hematopoiesis, in order to facilitate analysis of stem cell clonal histories. This result depended upon the use of unirradiated W/Wv newborn recipients. Before transplantation, viral integration markers were introduced during cocultivation of fetal liver or bone marrow cells with helper cell lines exporting defective recombinant murine retroviruses of the HHAM series. Omission of selection in culture [although the vector contained the bacterial neomycin-resistance (neo) gene] also limited the proportion of stem cells that were virally labeled. Under these conditions, engraftment was restricted to a small population of marked and unmarked normal donor stem cells, due to their competitive advantage over the corresponding defective cells of the mutant hosts. A relatively simple and coherent pattern emerged, of one or a few virally marked clones, in contrast to previous studies. In order to establish the totipotent hematopoietic stem cell identity of the engrafted cells, tissues were sampled for viral and inbred-strain markers for periods close to one year after transplantation. The virally labeled clones were characterized as stem cell clones by their extensive self-renewal and by formation of the wide range of myeloid and lymphoid lineages tested. Results clearly documented concurrent contributions of cohorts of stem cells to hematopoiesis. A given stem cell can increase or decrease its proliferative activity, become completely inactive or lost, or become active after a long latent period. The contribution of a single clone present in a particular lineage was usually between 5% and 20%.
Asunto(s)
Trasplante de Células Madre Hematopoyéticas , Retroviridae/genética , Animales , Animales Recién Nacidos , Trasplante de Médula Ósea , Células Clonales , ADN Viral/genética , ADN Viral/aislamiento & purificación , Feto , Células Madre Hematopoyéticas/citología , Células Madre Hematopoyéticas/microbiología , Trasplante de Hígado , Ratones , Ratones Endogámicos C57BL , Ratones Mutantes , Regiones Promotoras Genéticas , Mapeo RestrictivoRESUMEN
The development of a eutherian mammal as a male is a consequence of testis formation in the embryo, which is thought to be initiated by a gene on the Y chromosome. In the absence of this gene, ovaries are formed and female characteristics develop. Sex determination therefore hinges on the action of this testis-determining gene, known as Tdy in mice and TDF in humans. In the past, several genes proposed as candidates for Tdy/TDF have subsequently been dismissed on the grounds of inappropriate location or expression. We have recently described a candidate for Tdy, which maps to the minimum sex-determining region of the mouse Y chromosome. To examine further the involvement of this gene, Sry, in testis development, we have studied its expression in detail. Fetal expression of Sry is limited to the period in which testes begin to form. This expression is confined to gonadal tissue and does not require the presence of germ cells. Our observations strongly support a primary role for Sry in mouse sex determination.
Asunto(s)
Proteínas de Unión al ADN/genética , Análisis para Determinación del Sexo , Testículo/embriología , Animales , Secuencia de Bases , Expresión Génica , Edad Gestacional , Masculino , Ratones , Datos de Secuencia Molecular , Hibridación de Ácido Nucleico , Oligonucleótidos , Reacción en Cadena de la Polimerasa , ARN Mensajero/genética , Testículo/fisiologíaRESUMEN
During the critical period of mouse sex determination, mesenchymal cells migrate from the mesonephros into the adjacent developing testis. This process is thought to initiate cord development and is dependent on Sry. The presence of Sry, however, does not always guarantee normal testis development. For example, transfer of certain Mus domesticus-derived Y chromosomes, i.e., M. domesticus Sry alleles, onto the C57BL/6J (B6) inbred mouse strain results in abnormal testis development. We tested the hypothesis that mesonephric cell migration was impaired in three cases representing a range of aberrant testis development: B6 XY(AKR), B6 XY(POS), and (BXD-21 x B6-Y(POS))F1 XY(POS). In each case, mesonephric cell migration was abnormal. Furthermore, the timing, extent, and position of migrating cells in vitro and cord development in vivo were coincident, supporting the hypothesis that mesonephric cells are critical for cord development. Additional experiments indicated that aberrant testis development results from the inability of Sry(M. domesticus) to initiate normal cell migration, but that downstream signal transduction mechanisms are intact. These experiments provide new insight into the mechanism of C57BL/6J-Y(M. domesticus) sex reversal. We present a model incorporating these findings as they relate to mammalian sex determination.