Abbie Casper, Mark Van Doren. Dept Biology,
Johns Hopkins Univ, Baltimore, MD.
Sex-specific development of the germ cells is
critical for the formation of male or female gametes and the
continuation of a species. Previous work has shown that the decision
to develop as male or female in the germline is regulated by
non-autonomous
signals from the soma, and by germ cell autonomous cues regulated by
germ cell sex chromosome constitution. However, little is known
about how and when these signals interact to establish and maintain
germ cell sexual identity. Germ cell sex determination has mainly
been looked at during later stages of development and in adults, but
now new tools are allowing analysis of this process during
embryogenesis. To identify genes involved in germline sex
determination and development, a molecular screen was conducted
looking for genes expressed sex-specifically
in the embryonic germ cells. From this screen, eight genes were
found to be expressed sex-specifically in
the male germ line. Sex-specific expression
of some of these genes begins as early as stage 15 of embryogenesis
and is clear for all the genes by stage 17. Thus, it is likely that
germ cell sexual identity is being established during this time. We
are using these genes as indicators of germ cell sexual identity to
investigate how somatic signals and germ cell autonomous cues
control germ cell sex determination. We are currently investigating
how alterations in somatic sex (loss of function and gain of
function of transfomer), and mutations thought to affect germ cell
autonomous sexual identity (e.g . ovo and ovarian
tumor), affect the expression of our sex-specific
genes. Lastly, we are investigating the role of these genes in
sex-specific germ cell development. Viable
mutant alleles of one of our genes affect fertility in both sexes.
Mutant males are sterile with a severe depletion of germline stem
cells. In conclusion, from analysis of sex-specific
germ cell expression we are learning more about how and when initial
germ cell sexual identity is established, as well as how germline
sexual development is regulated at the molecular level. |