A network of C. elegans regulatory genes determines cell fate as either male or female. A central regulator of the network, TRA-2, promotes female fates in both the soma and germ line [1]. Spermatogenesis in the hermaphrodite germ line requires repression of
tra-2 translation through elements located in the
tra-2 3UTR [2]. Gain-of-function mutations that disrupt these translational control elements feminize XX germ lines, resulting in true females that make oocytes but no sperm. The sex determination phenotypes of
laf-1 mutations are similar to those of
tra-2 gain-of-function mutations, suggesting that
laf-1 plays a role in
tra-2 translational control. The germ lines of about 20% of XX
laf-1/+ heterozygotes are feminized and fail to produce sperm. A similar proportion of
laf-1/+ XO males exhibit both somatic and germline feminization [3]. Transgenic reporter constructs containing the
tra-2 3UTR are misregulated in
laf-1/+ heterozygotes [3], further supporting a role for
laf-1 in
tra-2 regulation. Laf-1 homozygotes are embryo and larval lethals, indicating that
laf-1 also functions outside of sex determination. I mapped
laf-1 using SNP markers to an 11 kb region containing two genes. Three independent
laf-1 alleles have missense mutations in Y71H2AM.19. Laf-1 encodes a member of a sub-family of DEAD-box RNA helicases that includes Drosophila Belle and Vasa. Laf-1 mutations cluster near a highly conserved motif in the helicase domain. Inhibiting expression of Y71H2AM.19 by RNAi causes a variety of phenotypes, including germ line feminization, sterility, growth defects, and embryonic lethality. The feminization and lethality phenotypes of Y71H2AM.19(RNAi) are similar to those of
laf-1 mutations, suggesting that the
laf-1 mutations are loss-of-function alleles. I am presently characterizing
laf-1 transcripts and determining their temporal and special patterns of expression, including possible sex-specific expression. Such information should clarify the functions of
laf-1 in sex determination and, possibly, in translational repression of
tra-2. References [1] Kuwabara et al (1992) Mol. Bio. of the Cell, 3: 461-473. [2] Goodwin et al (1993) Cell, 75: 329-339. [3] Goodwin et al (1997) Development, 124: 749-758.