Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 153-164). Available also in a digital version from Dissertation Abstracts.

The sex-determining gene on the Y chromosome, named Sry, initiates differentiation of gonadal somatic cells into testes, which in turn regulate the development of male phenotype. / The B6.YTIR sex-reversed mouse provides a good model for studying sex-determining mechanisms. We proposed a hypothesis that the testis-determining pathway is impaired downstream of Sry transcription in the B6.YTIR fetus. / The current study aimed to determine the hierarchical order of Sry, Sox9, Pn1, and Mis by examining their expression in B6.YTIR gonads as compared to normal B6.XY gonads by RT-PCR. / Results. Sry expression was comparable between B6.Y TIR and B6.XY gonads, with its onset between 10.5 and 11.5 dpc, a peak at 11.5 dpc, and downregulation thereafter. Sox9 expression was detectable in both B6.XX and B6.XY gonads at 11.5 dpc at comparable levels, but was then downregulated in B6.XX gonads at 12.5 dpc, by which stage testicular cord formation had began in B6.XY gonads. Pn1 was expressed in both B6.XX and B6.XY gonads at comparable levels at 11.5 dpc and was upregulated in B6.XY gonads at 12.5dpc. Mis expression in B6.Y TIR gonads was low at 10.5 and 11.5 dpc with a peak at 12.5dpc and higher levels only in ovotestes at 14.5dpc. / These results indicate that all Sox9, Pn1, and MIS genes follow a sexually dimorphic pattern of expression associated with development of testicular cords. Therefore, these genes are placed downstream of Sry in the fetal mouse gonad. Furthermore, we conclude that the testis-determining pathway is impaired upstream of Sox9 and Pn1 and Mis in the B6.YTIR gonad. (Abstract shortened by UMI.)

Sry on the Y-chromosome triggers the fetal gonad to begin differentiation into testis in mammals. Mutation or absence of Sry results in development of ovaries and the female phenotype. However, XY sex reversal in the presence of wild-type Sry exists in mice and man. One such example is the B6-YTIR mouse, whose autosomes and X-chromosome are of the C57BL6/J mouse (Mus musculus molossinus) whereas the Y-chromosome is from a mouse originating in Tirano, Italy (Mus musculus domesticus). B6-YTIR mice develop only ovaries or ovotestes in fetal life. The objective of my thesis was to identify the mechanism of sex reversal in the B6-YTIR mouse. The results indicate that onset of Sry transcription in B6-YTIR gonads is comparable to control B6 XY gonads. On the other hand, onset of Mis, 17alpha-HA, 3beta-HSD (testicular cell products), p450arom as well as inactivation of Sry transcription are delayed or absent in the sex reversed gonads. It has been suggested that low levels of Sry transcription may account for aberrant testis differentiation in B6-YTIR mice. We observed relatively low levels of Sry transcripts not only in B6-YTIR but also in B6 mice. However, levels in normal B6-YSJL mice were significantly greater. On the SJLB6F1 background, where no sex reversal occurs, Sry transcript levels of the TIR allele increased while those of B6 and SJL alleles remained the same as in the B6 background. Thus, low levels of Sry transcript from the B6 allele are sufficient whereas the levels from TIR and SJL alleles (both DOM type) appear to be critical for testis determination. We then compared the levels of endogenous Sry proteins. A combination of immunoprecipitation and immunoblotting succeeded in detecting a protein band whose expression profile and molecular size are consistent with those of the predicted Sry. Sry protein levels in B6-Y TIR gonads were roughly two fold greater than in B6 XY gonads. We hypothesize that the Sry protein of the TIR/SJL alleles is less efficient

Thesis (Ph. D. biochemistry)--Washington State University, May 2008. / Includes bibliographical references.

Inaug.-Diss.--Heidelberg. / Lebenslauf. "Benutzte literatur": p. [21]-22.

No description available.

No description available.

Florida’s sea turtle populations are increasing due to conservation efforts; however, sea turtle species are vulnerable to climate change. Turtles exhibit temperaturedependent sex determination, in which nest environment influences sex. Environmental changes may produce altered sex ratios that limit reproduction potential; therefore hatchling sex ratios should be monitored. Hatchlings are not externally sexually dimorphic, making sex identification difficult. This study established baseline plasma hormone concentrations in hatchling and post-hatchling green (Chelonia mydas) and loggerhead (Caretta caretta) sea turtles using High Performance Liquid Chromatography. Five hormones were assayed and were present in the majority of samples (testosterone: N.D.-10.12, progesterone: N.D.-0.43, estradiol: N.D.-4.78, estriol: N.D.-5.55 and estrone: N.D.-1.67 μg/mL). Plasma hormones did not distinguish hatchling sex because male and female ranges overlapped. Hormone concentrations varied with sex but also with incubation temperature, indicating that climate change could impact hatchling and posthatchling hormone profiles and thus could impact future fitness. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2016. / FAU Electronic Theses and Dissertations Collection

In order to combine previous observations from different sources on sex determination, and to identify sex chromosomes including the major sex determination locus in Nile tilapia, physical and genetic maps based on sex-linked markers and genes (such as sex-linked AFLPs, microsatellites, ovarian aromatase and DMO genes) were integrated and anchored. An accurate physical map using FISH techniques on mitotic cells was developed based on a previous map and 23 tilapia BAC clones previously assigned to linkage groups (LGs) 1, 3, 6, 7, 10 and 12; and on meiotic cells, 2 BAC clones containing the SLAM OniY227 and the dmrt4 gene were mapped. The six linkage groups were then assigned to different chromosomes, but surprisingly, the putative sex LG1 was located to a small submetacentric chromosome and not to the larger subtelocentric chromosome 1, where LG3 was assigned instead. The other LGs were assigned to different chromosomes and oriented with respect to the centromeres. A detailed comparison of the physical distribution of markers on chromosome 1 with respect to LG3 revealed a suppression in recombination in the subtelomeric region of the q arm between the marker GM354 (0 cM) and clcn5 (29 cM) and an abrupt increment of recombination between clcn5 (29 cM) and GM128 (77 cM) close to the centromere (Flpter=0.2). The unpairing region (20% of the total length) observed on the larger bivalents of XY fish during early pachytene in meiotic cells has been confirmed by DAPI staining and FISH to be at the terminal part of the q arm, opposite to the centromere. Comparison with six other tilapia species (2n=44) revealed a well conserved karyological distribution of the suspected LGs associated with sex determination (1 and 3). Besides, in O. karongae (2n=38) it was shown by SATA and UNH995/UNH104 marker hybridisation that LG1 has been re-arranged into the subtelomeric chromosome 2 as a result of a telomere-telomere fusion. A pool of 15 tilapia BAC clones previously localised on chromosome 1 and containing sex-linked AFLPs, dmrt1, dmrt4 and several SINEs were screened for new microsatellites; BACs were digested with SAU3AI and TC, GT, ATCT and CTGT probes radio-labelled with 32P. The high abundance of repetitive sequences in the BACs used led to only one useful polymorphic and co-dominant marker being obtained, associated to a BAC clone containing a copy of the dmrt1 gene on chromosome 1 (Flpter=0.85). Four linkage maps were constructed from an XY male, XY neofemale, XX neomale and XX female, mapping 4 and 8 markers on LG1 and LG3 (including the dmrt1 associated microsatellite) respectively. A specific sex-determination locus was identified on LG1 clearly linked with UNH995. However there appeared to be different allelic strengths for this sex determination locus, as shown by different sex ratios associated with different UNH995 genotypes. Additionally, one of the two XX fish mapped, showed the location of the recessive black blotching trait on LG3 (chromosome 1) between the markers GM128 and GM526, close to the centromere (Flpter=0.14). The results presented suggest a nascent Y chromosome in early stage of differentiation in Nile tilapia and with a functional master gene on LG1 close to the marker UNH995 (Flpter=0.67) located on the q arm of a small submetacentric chromosome. The potential influences of the autosomal LG3 (chromosome 1) in sex differentiation are also discussed.

In the B6.YTIR mouse strain, half of the XY progeny develop bilateral ovaries and the female phenotype. These XY females are infertile mainly due to the death of their embryos. This developmental failure has been attributed to a defect intrinsic to the XY oocyte. / The present study examined the transcriptional activity of the X and Y chromosomes in these oocytes. RT-PCR results show that the Ube1y gene is transcribed in the XY ovary at all stages examined and also in growing XY oocytes. The Sry gene was transcribed only at the onset of ovarian differentiation whereas the Zfy gene was undetectable at all stages during fetal life. The Xist gene, which is involved in X inactivation, was not expressed in XY oocytes. We speculate that expression of Y-encoded genes may have a deleterious effect on the quality of the oocytes and thus renders them incompetent for post-fertilization development.