Worm Breeder's Gazette 13(3): 41 (June 1, 1994)
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
In the C. elegans XX hermaphrodite, a transient period of spermatogenesis, confined to L4 ,allows the production of approximately 160 sperm in each gonad arm. A fate switch then occurs so that all additional germ cells enter oogenesis. We are interested in the regulatory mechanism that allows transient spermatogenesis.
Feminization of the Germ-line (Fog) We have performed a series of ablations to eliminate portions of the somatic gonad in late L2 (see figure in previous abstract). Ablation of 1 SS cell results in a gonad arm that is often feminized (45% Fog, n=119). Additionally, partial Fog arms are observed (10%), and some arms contain proximal undifferentiated cells (9%) that may have a confused gender identity. These ablations indicate that the SS cells, or their descendants, provide a transient signal for specification of the male germ cell fate.
The penetrance of Fog is incomplete (45%) in the 1 SS ablation, presumably because not all somatic structures that provide signal have been eliminated. Even ablation of 2 SS cells, which creates the miniature arms described in the previous abstract, does not eliminate all sperm production. We postulate that sperm are made in the miniature arms because other somatic cells in the primordium continue to provide enough signal. Consistent with this idea, we find that ablation of dorsal uterine cells can lead to low level Fog (<15%). Hypothetically, the entire somatic primordium, which comes into close contact with proximal germ cells in L2 and L3 ,is the source of the male fate signal.
Non-autonomy of hermaphrodite germ-line sex determination is not entirely unexpected. her-1 encodes a putative secreted product(1) that acts non-autonomously in XO male sex determination(2) and may interact with a receptor produced by tra-2 .(3)Mosaic analysis with her-1 has shown that in males, regulation of germ cell sexual fate is germ-line non-autonomous.(2) Indeed, expression of a her-1 construct in hermaphrodite body wall muscle can lead to overproduction of sperm.(1) Because her-1 (lf)has no effect in XX hermaphrodites, where the product is not expressed(4), we postulate that another signalling molecule is produced in hermaphrodites by the female somatic gonad to signal the male fate in the germ-line, possibly via TRA-2 .Based on genetic evidence, the best candidate for the signal is the product of the fog-2 gene.(5) Cloning of fog-2 is in progress.
We have also begun ablations in various mutants in an attempt to integrate ablation results with the known genetics of sex determination. We find, for example, that single SS ablations cannot suppress the Mog phenotype of fem-3 ( q20 gf)at 25°C.
Conclusions From these ablations, we conclude that a component of germ-line sex determination in the hermaphrodite is cell non-autonomous. Surprisingly, the female somatic gonad appears to signal the male germ cell fate.
(2) Hunter and Wood. Nature, 355:551-555, 1992.
(3) Kuwabara, et. al. Mol. Bio. Or the Cell, 3:461-473, 1992.
(4) Trent, et. al. Dev. Mech., 34:43-56, 1991.
(5) Schedl and Kimble. Genetics, 119:43-61, 1988.