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Evolution of Sex Determination

Penniman B. Austin seq4 at sfsuvax1.sfsu.edu
Fri Dec 9 07:36:06 EST 1994

Dear Hernan,

Since the SRY gene was discovered in 1990, deletions of the gene have been
demonstrated in XY sex-reversed females. More recently, sex reversal has been 
shown to occur in XY individuals with intact SRY genes, due to an overdose
of the X chromosome-linked SRVX/DSS gene. There is also an SRY homologue
on the X chromosome SOX3, which appears to be either the ancestor to SRY,
or to have evolved from a common ancestor. Do you know whether the SOX3
genes in sex reversed individuals are intact in XY female individuals? If
the SOX3 gene is found to have deletions in those with an intact  SRY
gene, this would deepen our understanding of the sex determination process
and investigate whether SOX3 plays any testis-determining role.
   The XX sex-reversed males studied so far have been discovered to have a
piece of the Y chromosome imbedded in the second X chromosome. Do you know
of any DNA studies done to determine whether  SOX3 and/or SRVX/DSS are
different in dosage or have deletions in sex reversed XX males when
compared with XX females? Do SOX3 and SRVX/DSS undergo or escape
X-inactivation under normal circumstances?

See Bardoni, et al (1994). A dosage sensitive locus at chromosome Xp21 is
involved in male to female sex reversal. Nat. Genet. 7:497-501.
Arn, P., et al (1994). SRVX, a sex reversing locus in Xp21,2->p22.11. Hum.
Genet. 93:389-393.
Foster, J.W., and Graves, J.A. (1994). An SRY-related sequence on the
marsupial X chromosome: implications for the evolution of the mammalian

Regards, Penniman

In article <3c6hc5$8r7 at vishnu.jussieu.fr>, Marc Girondot
<mgi at ccr.jussieu.fr> wrote:

> > Dear Penniman,
> > 
> > I am quite interested in these subjects and in particular in SRY / MIS
> > genes and in the origin of the mammalian male (which aparently is a 
> > highly modified female).
> > 
> > I would like to keep up in contact.
> > 
> > Greetings.
> > 
> > Hernan Lopez Schier
> > Facultad de Ciencias Exactas y Naturales
> > University of Buenos Aires
> > Argentina
> > e-mail: schierh at rocbi.dnet.roche.com
> Your proposition that mammalian male are highly modified female falls is
> the classical Jostian proposition of female as the neutral sex (Jost,
> 1972). This view has been emphatized by the finding of SRY, gene present
> on the Y chromosome. However, it is quite certain that an ovary is not
> the same as an undifferentiated gonad. Molecular marqueurs present in
> ovaries are absent undifferentiated gonads. Then the shemes of ganadal
> differentiation is better described as an undifferentiated gonad
> following two ways of differentiation. For the role of SRY there are two
> possibilities at the biochemical level:
> 1) Sry could be a promotor of male differentiation according to the
> Jostian hypothesis, female being the neutral sex
> 2) Sry could be a repressor of a constitutive female differentiation
> (McElreavey et al., 1993) from an undifferentiated gonad.
> In our group, we are working on the evolution of sex determination in
> vertebrates and we have developped an hypothesis of type 2 explaining the
> results obtained in all classes of vertebrates (Pieau et al., 1994a and
> b).
> Interesed in discussion.
> Marc Girondot
> Jost, A. - 1972 - A new look at the mechanisms controlling sex
> differentiation in mammals. Hopkins Med. J., 130: 38-53.
>  McElreavey, K., Vilain, E., Abbas, N., Herskowitz, I. and Fellous, M. -
> 1993 - A regulatory cascade hypothesis for mammalian sex determination:
> SRY represses a negative regulator of male development. Proc. Natl. Acad.
> Sci. USA, 90: 3368-3372.
> Pieau, C., Girondot, M., Desvages, G., Dorizzi, M., Richard-Mercier, N.
> and Zaborski, P. 1994. Environmental control of gonadal differentiation.
> In Short, R.V. and Balaban, E. (eds.), The differences between sexes.
> Cambridge Univ. Press, Cambridge, U.K., pp. 433-448.
> Pieau, C., Girondot, M., Desvages, M., Dorizzi, M., Richard-Mercier, N.
> and Zaborski, P. - 1994 - Temperature sensitivity of sexual
> differentiation of gonads in the european pond turtle: hormonal
> involvement. J. Exp. Zool., 269: 86-94.
> ________________________________________________________
> Marc Girondot                                                    Tel:
> (33) 1
> Laboratoire de Biochimie du Developpement      Fax: (33) 1
> Institut Jacques Monod                                      e-m:
> mgi at ccr.jussieu.fr
> 2 place Jussieu
> 75251 Paris Cedex 05
> France
> URL: http://bioldev1.ijm.jussieu.fr/IJM_HTTP/Francais/Girondot.html

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