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Sox9 Driven Sex Determination in Mice with Limited Y Chromosome Gene Contribution.

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Title:Sox9 Driven Sex Determination in Mice with Limited Y Chromosome Gene Contribution.
Authors:Ortega, Egle A.
Contributors:Developmental & Reprod Biology (department)
Keywords:sex determination
Y chromosome
male infertility
Date Issued:May 2018
Publisher:University of Hawaiʻi at Mānoa
Abstract:The window of sex determination is a short but critical time during which sex fate of the
embryo is decided depending on the chromosomal predisposition inherited from the parents. This
genetic information guides the direction of gonadal sex development towards acquisition of
anatomical male or female sexual characteristics. In most mammals, male sex determination is
initiated by expression of the Y chromosome encoded Sry. The duration of SRY signaling is
transient - just long enough to ensure upregulation of autosomally encoded Sox9. This way, SRY
acts as a molecular switch that initiates differentiation of the bipotential gonad into a testis.
However, once SRY signaling ceases, Sox9 remains at the center of male-specific molecular
signaling profile that ensures masculinization of the genital ridges. The focus of my dissertation
is on the effects of Sry-to-Sox9 replacement on the development of genital ridges, as well as
spermatogenesis and fertility in adult males.
Work presented here explores the hypothesis that transgenic overexpression of Sox9 can
replace the function of endogenous Sry at the time of sex determination and can sufficiently
support spermatogenesis and fertility in adult males. The sex-determining function of transgenic
Sox9 was tested using two genetic models: (1) mice that carried X chromosome and Y
chromosome lacking the endogenous Sry (XYTdym1); (2) mice that carried a single X chromosome
and lacked all endogenous Y chromosome genes (XO). The progression of spermatogenesis in
XYTdym1 males transgenic for Sox9 (XYTdym1Sox9) was assessed through various sperm and
testicular analyses such as sperm counts, motility, and morphology evaluation, as well testis
weight, shape, histology, vasculature assessment and mRNA expression levels. The fertility of
XYTdym1Sox9 males was tested through fecundity trials and in vitro (IVF). These investigations
revealed that despite some testicular abnormalities transgenic overexpression of Sox9 transgene
in the context of YTdym1 can replace the function endogenous Sry and allows for sufficient levels
of spermatogenesis and fertility.
In the mouse only two Y chromosome genes were shown to be necessary for successful
assisted reproduction: Sry and spermatogonial proliferation factor Eif2s3y. When Sry and Eif2s3y
were transgenically added to mice carrying a single X chromosome (XO), these mice
(XEif2s3yOSry) developed as phenotypic males and produced haploid gametes. The second part of
my dissertation, focuses on replacement of Sry and Eif2s3y with their non Y chromosome
encoded homologues, Sox9 and Eif2s3x. We found that males with Y chromosome genes limited
to two (XEif2s3yOSry), one (XOSry,Eif2s3x and XEif2s3yOSox9) or none (XOSox9,Eif2s3x) can
father offspring with assisted reproduction. However, we also observed that these males had
various abnormalities of the seminiferous epithelium and testicular interstitium. Moreover,
sometimes the gonads of the transgenic males resembled ovotestes and had elevated expression
of ovarian markers. These findings led to a hypothesis that pathologies observed in males with
limited Y chromosome genes arise at the time of sex determination due to altered signaling in the
genital ridges. To test this hypothesis, I compared gonadal development in males without Y
chromosome and in which sex determination is initiated either by Sry or Sox9, and
spermatogenesis is driven by either Eif2s3y or Eif2s3x. My findings support the initial hypothesis
and suggest that all XO males with limited Y chromosome genes have altered gonadal
development at the critical time of sex determination. The failure to completely antagonize
female specific signaling and establish characteristic male-like gonadal morphology is especially
prominent in genotypes that have sex determination driven by transgenic overexpression of Sox9.
Description:Ph.D. Thesis. University of Hawaiʻi at Mānoa 2018.
Rights:All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.
Appears in Collections: Ph.D. - Developmental and Reproductive Biology

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