Wang S et al. (2001) EMBO J "The TRA-1 transcription factor binds TRA-2 to regulate sexual fates in Caenorhabditis elegans."

Wang S, Kimble J

[EMBO J, 2001]

The tra-1 and tra-2 sex-determining genes promote female fates in Caenorhabditis elegans. Classical genetic studies placed tra-1 as the terminal regulator of the pathway with tra-2 acting upstream as a regulator of regulators of tra-1. Here we report the surprising result that the TRA-1 transcription factor binds the intracellular domain of the TRA-2 membrane protein. This binding is dependent on the MX regulatory domain, a region of the TRA-2 intracellular domain shown previously to be critical for the onset of hermaphrodite spermatogenesis. The functional importance of the TRA-1-TRA-2 physical interaction is supported by genetic interactions between tra-1(0) and tra-2(mx) mutations: a reduction of tra-1 gene dose from two copies to one copy enhances the tra-2(mx) feminization phenotype, but has no apparent somatic effect. In Caenorhabditis briggsae, we also find an MX-dependent interaction between Cb-TRA-1 and Cb-TRA-2, hut intriguingly, no cross-species interactions are seen. The conservation of the TRA-1-TRA-2 interaction underscores its importance in sex determination.

Lum DH et al. (2000) Genes Dev "Direct protein-protein interaction between the intracellular domain of TRA-2 and the transcription factor TRA-1A modulates feminizing activity in C. elegans."

Zarkower D, Spence AM, Lum DH, Kuwabara PE

[Genes Dev, 2000]

In the nematode Caenorhabditis elegans, the zinc finger transcriptional regulator TRA-1A directs XX somatic cells to adopt female fates. The membrane protein TRA-2A indirectly activates TRA-1A by binding and inhibiting a masculinizing protein, FEM-3. Here we report that a part of the intracellular domain of TRA-2A, distinct from the FEM-3 binding region, directly binds TRA-1A. Overproduction of this TRA-1A-binding region has tra-1-dependent feminizing activity in somatic tissues, indicating that the interaction enhances TRA-1A activity. Consistent with this hypothesis, we show that tra-2(mx) mutations, which weakly masculinize somatic tissues, disrupt the TRA-2/TRA-1A interaction. Paradoxically, tra-2(mx) mutations feminize the XX germ line, as do tra-1 mutations mapping to the TRA-2 binding domain. We propose that these mutations render tra-2 insensitive to a negative regulator in the XX germ line, and we speculate that this regulator targets the TRA-2/TRA-1 complex. The intracellular domain of TRA-2A is likely to be produced as a soluble protein in vivo through proteolytic cleavage of TRA-2A or through translation of an XX germ line-specific mRNA. We further show that tagged derivatives of the intracellular domain of TRA-2 localize to the nucleus, supporting the hypothesis that this domain is capable of modulating TRA-1A activity in a manner reminiscent of Notch and Su(H).

Kuwabara PE (1996) Genetics "Interspecies comparison reveals evolution of control regions in the nematode sex-determining gene tra-2."

Kuwabara PE

[Genetics, 1996]

The Caenorhabditis elegans sex-determining gene tra-2 promotes female development and expresses 4.7-, 1.9- and 1.8-kb mRNAs. The 4.7-kb mRNA encodes the major feminizing activity of the locus, a predicted membrane receptor that mediates cell-to-cell communication, named TRA-2A. The tra-2 gene was characterized from a close relative, C. briggsae. The Cb-tra-2 gene expresses only a 4.7-kb mRNA and alternatively spliced variants, which encode TRA-2A homologues. The Cb-TRA-2A and Ce-TRA-2A sequences are highly diverged, sharing only 43% identity, although their hydropathy profiles remain remarkably similar. Three potential regulatory sites of Ce-tra-2 activity were previously identified by analyzing tra-2(eg), tra-2(gf), and tra-2(mx) mutations. Two of these sites, the EG site and MX region, are conserved in Cb-tra-2. By contrast, the two direct repeat elements in the Ce-tra-2 3' untranslated region, which are disrupted in tra-2(gf) mutants, are absent. Injection of Cb-tra-2 antisense RNA into C.briggsae mimics the Ce-tra-2 loss-of-function phenotype. Thus, antisense RNA permits studies of gene activity in nematodes that lack extensive genetics.

Segal SP et al. (2001) Dev Cell "RNA-Regulated TRA-1 nuclear export controls sexual fate."

Graves LE, Segal SP, Goodwin EB, Verheyden J

[Dev Cell, 2001]

TRA-1, a member of the GLI family of transcription factors, is required for C. elegans female development. We find that TRA-1 has a sex-specific distribution consistent with its role in female development: nuclear TRA-1 is higher in hermaphrodite intestines and in specific germline regions than in males. TRA-1 patterns rely on nuclear export since treatment with leptomycin B, a CRM1-dependent export inhibitor, increases nuclear TRA-1 in males. TRA-1 export requires TRA-1 binding to the tra-2 3' untranslated region (3' UTR), as disruption of binding increases nuclear TRA-1 and female development. Our data are consistent with coexport of a TRA-1/tra2 mRNA complex reducing TRA-1 nuclear activity, and identify an interesting RNA-based mechanism for controlling transcriptional activity and cell fate determination.

De Bono M et al. (1996) Genetics "Evolution of sex determination in caenorhabditis: unusually high divergence of tra-1 and its functional consequences."

Hodgkin JA, De Bono M

[Genetics, 1996]

The tra-1 gene is a terminal regulator of somatic sex in Caenorhabditis elegans: high tra-1 activity elicits female development, low tra-1 activity elicits male development. To investigate the function and evolution of tra-1, we examined the tra-1 gene from the closely related nematode C. briggsae. Ce-tra-1 and Cb-tra-1 are unusually divergent. Each gene generates two transcripts, but only one of these is present in both species. This common transcript encodes TRA-1A, which shows only 44% amino acid identity between the species, a figure much lower than that for previously compared genes. A Cb-tra-1 transgene rescues many tissues of tra-1(null) mutants of C. elegans but not the somatic gonad or germ line. This transgene also causes nongonadal feminization of XO animals, indicating incorrect sexual regulation. Alignment of Ce-TRA-1A and Cb-TRA-1A defines several conserved regions likely to be important for tra-1 function. The phenotypic differences between Ce-tra-1(null) mutants rescued by Cb-tra-1 transgenes and wild-type C. elegans indicate significant divergence of regulatory regions. These molecular and functional studies suggest that evolution of sex determination in nematodes is rapid and genetically complex.

Kuersten S et al. (2004) Mol Cell "NXF-2, REF-1, and REF-2 affect the choice of nuclear export pathway for tra-2 mRNA in C. elegans."

Kuersten S, LaMartina SM, Verheyden J, Goodwin EB, Segal SP

[Mol Cell, 2004]

In C. elegans, tra-2 mRNA nuclear export is controlled by a 3''UTR element, the TRE. In the absence of TRA-1, the TRE retains tra-2 mRNA in the nucleus. The binding of TRA-1 to the 3''UTR overcomes this retention resulting in export of a TRA-1/tra-2 mRNA complex. Here, we find that, unlike most mRNAs, tra-2 mRNA exits the nucleus via an alternative pathway to NXF-1 that requires CRM1 activity. Inhibition of export by NXF-1 depends upon the TRE, CeNXF-2, CeREF-1, and CeREF-2. Removal of the TRE or any one of these factors results in export of tra-2 by NXF-1. NXF-2 and REF-1 specifically bind the TRE, suggesting that they directly control tra-2 mRNA export. Furthermore, choice of proper export pathway affects tra-2 translational control. Therefore, tra-2 mRNA export is highly regulated and plays an important role in development by regulating the activity of tra-2 mRNA in the cytoplasm.

Kuwabara PE et al. (1995) Development "A predicted membrane protein, TRA-2A, directs hermaphrodite development in Caenorhabditis elegans."

Kuwabara PE, Kimble JE

[Development, 1995]

The nematode C. elegans naturally develops as either an XO male or XX hermaphrodite, The sex-determining gene, tra-2, promotes hermaphrodite development in XX animals, This gene encodes a predicted membrane protein, named TRA-2A, which has been proposed to provide the primary feminising activity of the tra-2 locus, Here, we show that transgenic TRA-2A driven from a heat shock promoter can fully feminise the somatic tissues of XX tra-2 loss-of-function mutants, which would otherwise develop as male. TRA-2A is thus likely to provide a component of the tra-2 locus that is both necessary and sufficient to promote female somatic development, Transgenic TRA-2A driven by the heat shock promoter can also transform XO animals from male to self-fertile hermaphrodite, This result establishes the role of tra-2 as a developmental switch that controls somatic sexual cell fate, We show that a carboxy-terminal region of TRA-2A, predicted to be intracellular, can partially feminise XX tra-2 loss-of-function mutants and XO tra-2(+) males, We suggest that this intracellular domain of TRA-2A promotes hermaphrodite development by negatively regulating the FEM proteins.

Kuwabara PE et al. (1998) Dev Biol "Germ-line regulation of the Caenorhabditis elegans sex-determining gene tra-2."

Kuwabara PE, Kimble JE, Okkema PG

[Dev Biol, 1998]

The Caenorhabditis elegans sex-determining gene tra-2 promotes female development of the XX hermaphrodite soma and germ line. We previously showed that a 4.7-kb tra-2 mRNA, which encodes the membrane protein TRA-2A, provides the primary feminizing activity of the tra-2 locus. This paper focuses on the germ-line activity and regulation of tra-2. First, we characterize a 1.8-kb tra-2 mRNA, which is hermaphrodite-specific and germ-line-dependent. This mRNA encodes TRA-2B, a protein identical to a predicted intracellular domain of TRA-2A. We show that the 1.8-kb mRNA is oocyte-specific, suggesting that it is involved in germ-line or embryonic sex determination. Second, we identify a tra-2 maternal effect on brood size that may be associated with the 1.8-kb mRNA. Third, we investigate seven dominant tra-2(mx) (for mixed character) mutations that sexually transform hermaphrodites to females by eliminating hermaphrodite spermatogenesis. Each of the tra-2(mx) mutants possesses a nonconserved missense change in a 22-amino-acid region common to both TRA-2A and TRA-2B, called the MX region. We propose that the MX region mediates a posttranslational regulation of tra-2 essential for the onset of hermaphrodite spermatogenesis. Finally, we discuss aspects of tra-2 function and regulation that are specific to the unusual control of cell fate in the hermaphrodite germ line.

Rankin CH J Neurogenet "But can they learn? My accidental discovery of learning and memory in C. elegans."

Rankin CH

[J Neurogenet]

I did not set out to study <i>C. elegans</i>. My undergraduate and graduate training was in Psychology. My postdoctoral work involved studying learning and memory in 1mm diameter juvenile <i>Aplysia californica</i>. As a starting Assistant Professor when I attempted to continue my studies on Aplysia I encountered barriers to carrying out that work; at about the same time I was introduced to <i>Caenorhabditis elegans</i> and decided to investigate whether they could learn and remember. My laboratory was the first to demonstrate conclusively that <i>C. elegans</i> could learn and in the years since then my lab and many others have demonstrated that <i>C. elegans</i> is capable of a variety of forms of learning and memory.

Hodgkin JA et al. (1977) Genetics "Mutations causing transformation of sexual phenotype in the nematode Caenorhabditis elegans."

Brenner S, Hodgkin JA

[Genetics, 1977]

Ten mutations are described that transform genotypic hermaphrodites of the nematode Caenorhabditis elegans into phenotypic males. These fall into three autosomal complementation groups, termed tra-1, tra-2, and tra-3. Two alleles of tra-1 produce almost complete transformation, to a fertile male phenotype; such transformed animals are useful for analyzing sex-linked genes. All alleles of tra-1 and tra-2 are recessive; the one known allele of tra-3 is both recessive and maternal in effect. Where tested, both XX and XXX hermaphrodites are transformed into males, but XO males (true males) are unaffected by these mutations. It is suggested that these genes are actually involved in hermaphrodite development and have no role in male development.