Worm Breeder's Gazette 10(3): 14
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.
The fem--3(+) gene specifies male development. In XX hermaphrodites, fem-3 is required only in the germline: it must first be active to direct spermatogenesis and then it must be packaged into oocytes for a maternal contribution to the embryo. This maternal product must be negatively regulated so that it will not transform oocyte precursors into sperm. Nine temperature sensitive gain-of-function (gf) alleles of fem-3 cause the aberrant production of a vast excess of sperm in hermaphrodites; no oocytes are made, and no alteration is observed in the hermaphrodite soma. Genetic studies suggest that fem-3(gf) mutations do not increase fem-3(+) activity, but instead produce a novel unregulated product (1). The germline-specific masculinization of fem-3(gf) is consistent with the finding that fem-3 RNA's are limited to the germline in hermaphrodites (2). The wild-type fem-3 gene has been cloned, and its sequence and gene structure elucidated ( 2; Rosenquist, unpublished). We have cloned all nine fem-3(gf) genes. We sequenced one fem-3(gf) allele, q20, in its entirety and found a single base pair change in the 3' untranslated region (3'-UTR). Partial sequencing of the rightmost eight fem-3(gf) alleles similarly reveal changes in the 3'-UTRs. The two weak fem-3(gf) alleles are both T to C changes of the same base pair; the five intermediate fem-3( gf) alleles are all C to T changes of an adjacent base pair; and the one strong fem-3(gf) allele is a G to T change a few bases pairs 3' of the other mutations (see figure). One super strong fem-3(gf), q95, which is barely temperature sensitive, is a 114bp deletion centered around the region of the point mutants and contained within the 3'-UTR, It may be significant that most of the fem-8(gf) mutants lie in a CTT repeat. The short sequence in the 3'-UTR that has been shown by transformation experiments to be important to unc-54 function also contains a CTT repeat (Fire, WBG 10 No. 2); furthermore, this region is conserved in the 3'-UTR of the mlc-1 gene (Cummins and Anderson, pers . comm. ) . The clustering of these fem-3(gf) base pair changes within a stretch of five base pairs indicates that this small region is centrally involved in the regulation of fem-3. The temperature sensitivity of the mutations suggests the involvement of an RNA/RNA or RNA/protein interaction. In searches for secondary structure in the region, there is no striking stem including or near the base pairs identified by mutation. The negative regulation of fem- 3 activity identified by the mutations may act through RNA stability, efficiency of translation, or localization of the RNA within the germ line.