Functional dissection of the gene, bli-4, in Caenorhabditis elegans

The bli-4 gene of Caenorhabditis elegans encodes at least four gene products by the mechanism of alternative splicing. Termed blisterases A-D, these isoforms contain unique carboxyl termini and exhibit distinct structural homology to different members of the kexin family of proprotein convertases. Two different kinds of phenotypes have been identified in our collection of bli-4 mutants: blistering at the adult stage of the allele e937, and embryonic (or early larval) lethality of thirteen alleles, suggesting bli-4 plays a functional role not only in the assembly or maintenance of the adult cuticle but also in the early development of the animal. The goal of this thesis is to investigate the functions of the individual blisterases using isoform-specific minigenes in a bli-4 mutant background. Three minigenes were constructed. Together with pCeh226 containing the carboxyl terminus for blisterase A , these constructs provide minigenes specific for three of the isoforms, pCeh299 for blisterase B, pCeh308 and pCeh309 for blisterase C. The blistered mutant lacks the 3' exon of blisterase A. As expected, a high copy number of the minigene providing the blisterase A isoform rescued this phenotype. In addition, the blisterase A minigene also rescued the lethal mutants, suggesting either that blisterase A is required early in development or inappropriately provides the function of the other isoforms. At high copy number, the blisterase B minigene also rescued both the blistering and the lethal phenotypes whereas a modified blisterase C minigene (pCeh309) only rescued the blistering phenotype. At low copy number, three out of five transgenic lines containing the blisterase B minigene and one putative integrated line containing blisterase C (pCeh308) also rescued blistering. None of the arrays carrying a low copy number of minigenes rescued the lethal mutants tested. The results support the hypothesis that high copy number lines can inappropriately provide the function of other isoforms. This is compatible with the suggestion that there is functional redundancy between the isoforms, with blisterases A and B probably playing a more important role than blisterase C as indicated by the present results. Biological specificity may result from the developmental, or tissue-specific distribution of the processing enzyme with its substrate.Medicine, Faculty ofMedical Genetics, Department ofGraduat