Worm Breeder's Gazette 15(1): 75 (October 1, 1997)
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.
| 1 | University of Minnesota Medical School, Minneapolis, MN, 55455 USA |
| 2 | MRC-LMB, Hills Road, Cambridge CB2 2QH, UK |
The mab-3 gene has two roles in male sexual development: it is
required for differentiation of the V ray neuroblasts in the male
peripheral nervous system and it is required to prevent vitellogenin
gene transcription in the male intestine. mab-3 is not required in
hermaphrodites. We have cloned mab-3 and find that it is related to
the Drosophila melanogaster sexual regulatory gene doublesex (dsx).
This is the first molecular similarity between phyla in sex-determining
pathways.
Mapping placed mab-3 in a "YAC bridge." We cloned random small
DNA fragments from a YAC, Y53C12, known to contain mab-3, and
identified clones that were neither yeast nor sequenced nematode DNA.
We positioned these fragments relative to adjacent contigs by
long-range PCR, and chose one likely to lie near mab-3. Using this DNA
as a probe, we isolated phage clones from a library of yeast containing
the YAC, and showed by transformation rescue that one phage contained
mab-3.
The minimal rescuing region can encode a protein with two
copies of a DNA binding motif resembling that of the Doublesex
proteins. This motif, which we have named the DM domain, is similar to
but distinct from a zinc finger. We have found mutations in all six
mab-3 alleles. e1921 has a Cys to Tyr mutation in the first DM domain,
and the canonical null allele e1240 has a Cys to Tyr mutation in the
second DM domain, showing that both domains are important for mab-3
activity.
The mab-3 gene expresses three mRNAs. Two are trans-spliced to
SL1, and one has an alternative exon with stop codons in all frames.
The
two shorter mRNAs appear to be minor and non-functional. The
full-length mRNA is more abundant in males than hermaphrodites. In
tra-1(null) XX pseudomales, this mRNA accumulates to normal male
levels, indicating that its levels are controlled by tra-1.
The sequence similarity of mab-3 to doublesex reflects similar
roles of the two genes. Both genes control sex-specific neuroblast
differentiation and yolk protein gene transcription; dsx controls other
sexually dimorphic features as well. The two genes are functionally
related as well: a cDNA encoding the male splice form of DSX, expressed
by heatshock, can restore V rays to a mab-3 mutant. In contrast,
female DSX has no effect. This structural and functional conservation
between phyla suggests a common evolutionary origin of at least some
aspects of sexual regulation.