C. elegans compensates for the difference in X chromosome dose between males and hermaphrodites by equalizing X-linked transcript levels between the sexes. The genes
dpy-26, ntial components of this dosage compensation process in XX animals. Mutations in any of these genes cause elevated X-linked transcript levels in XX animals and an incompletely penetrant maternal-effect XX-specific lethality. While XO dpy animals are fully viable, wild-type males, XX dpy animals that escape the lethality are Dpy and Egl. Genetic analysis of these genes suggests that they act together to regulate X chromosome expression. However, the mechanism by which they achieve this regulation is unknown. In order to understand the mechanism of dosage compensation, we have undertaken a molecular approach to study the function of
dpy-27. dpy- 27 maps within the 3.5 map unit interval between the two cloned genes
unc-93 and
ced-4. These two endpoints define a region of approximately 800 kb on the contig that should contain the
dpy-27 locus. Using RFLP's between N2 and AB2 (Adelaide, Australia), we mapped
dpy-27 between the cosmids C14B1 and C36E8. Further localization of
dpy-27 came from the finding that
pat-3, recently shown to reside on cosmid ZK1058, maps very close to, or to the right of
dpy-27 (S. Gettner, J. Plenefisch, personal communications). With this combined information, we attempted to rescue the
dpy-27 maternal-effect lethal phenotype by germline transformation using cosmids from the region. Pools of cosmids were coinjected with the dominant
rol-6 (pRF4) marker into
dpy-27(
y57) animals. The F1 roller progeny were scored for rescue of the Dpy, Egl, PvuI phenotypes characteristic of survivors of the
dpy-27 maternal-effect lethality. Once rescue was obtained, we localized the rescuing activity to cosmid C17A5. Rescued animals range in phenotype from wild-type length to slightly Dpy, Egl and PvuI. This range of phenotypes occurs in both F1 rescued animals and in transmitting lines carrying the extrachromosomal array. Preliminary results indicate that a 14 kb subclone of C17A5 also contains rescuing activity. We are currently in the process of defining the minimal region required for rescue, searching for allele-specific polymorphisms, and determining the transcripts located in the rescuing region. [See Figure 1]