Evolution of Sex Determination

Marc Girondot mgi at ccr.jussieu.fr
Thu Dec 8 03:50:13 EST 1994

> 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

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

URL: http://bioldev1.ijm.jussieu.fr/IJM_HTTP/Francais/Girondot.html

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