The combgap locus encodes a zinc-finger protein that regulates cubitus interruptus during limb development in Drosophila melanogaster.

The combgap locus, first described by C. B. Bridges in 1925, is a gene required for proper anteroposterior pattern formation in the limbs of Drosophila melanogaster. The development of the anteroposterior axis of fly limbs is initiated by hedgehog signaling from cells of the posterior half to cells of the anterior half of the limb primordium. Hedgehog signaling requires the anterior-specific expression of the gene cubitus interruptus to establish posterior-specific hedgehog secretion and anterior-specific competence to respond to hedgehog. We have cloned combgap and find that it encodes a chromosomal protein with 11 C(2)H(2) zinc fingers. Limb defects found in combgap mutants consist of either loss or duplication of pattern elements in the anteroposterior axis and can be explained through the inappropriate expression of cubitus interruptus and its downstream target genes. In combgap mutants, cubitus interruptus is ectopically expressed in the posterior compartments of wing imaginal discs and is downregulated in the anterior compartment of legs, wings and antennae. We are able to rescue anterior compartment combgap phenotypes by expressing additional cubitus interruptus using the Gal4/UAS system. Dominant alleles of cubitus interruptus, which result in posterior expression, phenocopy combgap posterior compartment phenotypes. Finally, we find that the combgap protein binds to polytene chromosomes at many sites including the cubitus interruptus locus, suggesting that it could be a direct regulator of cubitus interruptus transcription.

The mouse uracil-DNA glycosylase gene: isolation of cDNA and genomic clones and mapping ung to mouse chromosome 5.

Uracil-DNA glycosylase (UDG) is the enzyme responsible for the first step in the base-excision repair pathway that specifically removes uracil from DNA. Here we report the isolation of the cDNA and genomic clones for the mouse uracil-DNA glycosylase gene (ung) homologous to the major placental uracil-DNA glycosylase gene (UNG) of humans. The complete characterization of the genomic organization of the mouse uracil-DNA glycosylase gene shows that the entire mRNA coding region for the 1.83-kb cDNA of the mouse ung gene is contained in an 8.2-kb SstI genomic fragment which includes six exons and five introns. The cDNA encodes a predicted uracil-DNA glycosylase (UDG) protein of 295 amino acids (33 kDa) that is highly similar to a group of UDGs that have been isolated from a wide variety of organisms. The mouse ung gene has been mapped to mouse chromosome 5 using fluorescence in situ hybridization (FISH).

The C. elegans neuronally expressed homeobox gene ceh-10 is closely related to genes expressed in the vertebrate eye.

We describe the homeobox gene ceh-10 from the nematode Caenorhabditis elegans. The homeodomain of ceh-10 is closely related to the homeodomains of two genes recently cloned from the vertebrate retina, Chx10 from mice and Vsx-1 from goldfish. We show that the sequence conservation extends well beyond the homeodomain and includes a region (named the CVC domain) of roughly 60 amino acids immediately C-terminal to the homeodomain. As assayed in transgenic worms, the promoter region of ceh-10 directs expression of a lacZ reporter gene to a small number of neurons. We draw a parallel between the bipolar cells of the inner nuclear layer of the vertebrate retina, which express Chx10 and Vsx-1, and an interneuron in C. elegans called AIY, which expresses ceh-10. AIY receives synaptic input from a sensory cell, just as do bipolar cells of the vertebrate retina. In C. elegans, the sensory cell AFD is not known to be photosensitive but is known to be thermosensitive; moreover, a cell with similar position in the amphids of other nematodes has been suggested indeed to be photosensitive. Our results emphasize the highly conserved nature of sensory regulatory mechanisms and suggest one way in which photosensitive organelles might have originated in evolution.

Production of null mutants in the major intestinal esterase gene (ges-1) of the nematode Caenorhabditis elegans.

The ges-1 gene of the nematode Caenorhabditis elegans codes for a nonspecific carboxylesterase that is expressed only in the intestinal lineage. This esterase has turned out to be a convenient biochemical marker for lineage-specific differentiation. In the present paper, we describe the production of several C. elegans strains that lack detectable activity of the ges-1 esterase. To isolate these ges-1 null strains, we first produced a strain of hermaphrodites in which the wild-type copy of the ges-1 gene was stably balanced over a previously isolated isoelectric focusing allele, ges-1(ca6); this parental strain was then mutagenized with EMS and isoelectric focusing gels were used to identify progeny populations that lacked either ges-1(+) or ges-1(ca6) esterase activity. This method is a straightforward and general approach to obtaining null mutations in any gene that has a biochemical or immunological assay. The ges-1 gene is not essential to worm survival, development or reproduction. Furthermore, lack of the ges-1 product has no obvious effect on the ability of worms (containing either normal or greatly reduced levels of acetylcholinesterases) to survive exposure to esterase inhibitors. The ges-1 gene product provides roughly half of the total esterase activity measured in crude extracts of L1 larvae or mixed worm populations. However, histochemical staining of individual ges-1(0) embryos shows that the ges-1 esterase is the first and essentially the only esterase to be produced during embryonic development, from the midproliferation phase up to at least the twofold stage of morphogenesis. These ges-1(0) strains now allow us to investigate the developmental control of the ges-1 gene by DNA-mediated transformation, in which the ges-1 gene acts as its own reporter.