Isolation and Characterisation of Four Cathepsin B-Like Cysteine Protease Genes From the Free Living Nematode Caenorhabditis elegans

The cathepsin B cysteine protease enzyme performs a role in protein turnover and degradation within the lysosomes of vertebrates. This proteolytic enzyme is also thought to perform related roles in the processing of antigens and protein precursors, as well as a role in bone resorption. A pathological role for cathepsin B in tumour cell invasion has also been suggested. Enzymes with cathepsin B-like activities are thought to be excreted and/or secreted by a variety of parasitic nematode and trematode species. To date, multigene families with the potential to encode cathepsin B-like enzymes have only been reported in parasitic nematode and trematode species, suggesting that these enzymes may be important for parasitism by these species. The work presented in this thesis demonstrates that the free living nematode species, Caenorhabditis elegans, also possesses a cathepsin B-like multigene family indicating that such multigene families are not unique to parasitic nematode and trematode species. Four genes with homology to vertebrate cathepsin B were isolated from the genome of C. elegans and were named cpr-3, cpr-4, cpr-5 and cpr-6. Phylogenetic analysis clusters the proteins encoded by these four genes with known cathepsin B enzymes and away from other, related enzymes such as cathepsins H and L. Since the four genes possess distinct genomic architectures, they appear to have arisen from ancient gene duplication events. This is supported by phylogenetic analysis which clusters the predicted proteins encoded by these four genes and cpr-1, a previously isolated C.elegans cathepsin B-like gene (Ray and McKerrow, 1991), into three groups which are almost as diverged from one another as each is to the vertebrate cathepsin B enzymes. The expression of cpr-3, cpr-4, cpr-5 and cpr-6 as lacZ reporter transgene fusions in transgenic worms suggests that these four genes are all exclusively expressed in the intestinal cells of C. elegans. Analysis of the temporal expression patterns of these four genes using semi-quantitative reverse transcription polymerase chain reaction indicates that the four genes exhibit distinct but overlapping temporal patterns of expression during C. elegans development. These results suggest a differential requirement for cathepsin B-like enzymes, or combinations of enzymes, within the intestine during C. elegans development