Worm Breeder's Gazette 13(3): 34 (June 1, 1994)
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.
We are interested in studying the transition from maternal to zygotic control during development of the C elegans embryo. The analysis of the transcriptional regulation of early zygotically activated genes might lead to a better understanding of how the embryo takes over control of its own developmental fate. For this purpose, we have isolated two mutations (named ca201 and ca202 )that lead to arrest during early morphogenesis of the embryo due to zygotic expression of the mutant genes. Most of development up to this point seems to depend on maternal factors. Homozygous ca201 embryos arrest at early elongation, whereas ca202 embryos don't seem to elongate at all and instead seem to burst at the ventral surface, thereby allowing internal cells to flow out. ca201 was mapped to the unc-57 unc-38 interval on LGI and ca202 was placed between daf-11 and sma-1 in the region uncovered by ctDf1 on LGV. Placing these mutations under deficiencies indicates that ca202 is likely to be a null, whereas ca201 doesn't seem to be a null allele. We have concentrated our efforts on characterizing ca201 genetically and cloning the gene. The genetic highlights are:
1. ca201 is an allele of let-502 since ca201 fails to complement any of the five known let-502 alleles ( h392 , h509 , h732 , h783 and h835 ;kindly supplied by Ann Rose and Mark Edgley)
2. ca201 seems to be a weak 'gain of function' allele although ca201 /+animals are usually wildtype (occasional rollers or other deformations are observed)
3. All of the six let-502 alleles seem to be antimorphs.
4. The six let-502 alleles result in different arrest stages when homozygous: ca201 , h835 (early elongation); h783 (early elongation to early larval); h732 (mid larval); h392 , h509 (late larval).
5. let-502 is expressed both maternally and zygotically.
6. The maternal contribution of wildtype let-502 can partially rescue homozygous mutant worms, leading to later arrest stages. This is dependent on the relative gene dosage of wildtype let-502 to the mutant allele.
7. The maternal contribution of let-502 ( ca201 )leads to an earlier arrest stage for progeny that are homozygous for a less severe let-502 allele (i.e. homozygous ( h392 )arrest at early elongation = ca201 phenotype)
Cosmids that span the unc-57 unc-38 interval were tested for rescue of the ca201 mutant phenotype. This interval contains two gaps that are covered by YACs. A pool of 8 cosmids (concentrations of the individual cosmids ranged from 0.25 to 1 µg/ml and l00 µg/ml for pRF4 )was able to rescue ca201 ,although the rescued worms were sterile .Two single cosmids were also able to rescue ca201 ,although again the rescued worms were sterile. These two cosmids ( C10H11 and K06G1 )overlap extensively on the physical map. DNA fragments that span this overlapping region are now being subcloned and tested for rescue of ca201 .