Expression and secretion of a larval-specific chitinase (family 18 glycosyl hydrolase) by the infective stages of the parasitic nematode, Onchocerca volvulus

A recently reported chitinase gene, expressed in the infective, third-stage (L3) larvae of the human filarial parasite Onchocerca volvulus, belongs to the family 18 glycosyl hydrolases and has been designated Ov-chi-1. The ge ne product of Ov-chi-1 is chitinolytic. Allosamidin ablates activity of the native enzyme in a dose-dependent manner but did not significantly inhibit the moulting of L3 larvae. Mono-specific antibodies were used to character ize Ov-CHI-1 as a 60-kDa protein expressed almost exclusively in L3 stages. Immunoelectron microscopy showed that Ov-CHI-1 expression is initiated in late L2 larvae and increases markedly in infective, L3 larvae. It is synthe sized exclusively in the glandular esophagus and stored within discrete sec retory granules. Secretion occurs through de-granulation during post-infect ive development, and the primary route of transport appears to be via the p seudo-coelom. An orthologue of Ov-chi-1 was detected in Caenorhabditis eleg ans by BLAST analysis. It is constitutively expressed at a low level and is overexpressed in dauer larvae and embryonated eggs. It is chitinolytic. We conclude that Ov-CHI-1 is a highly stage-specific enzyme that may have a r ole in infectivity of the parasite, aiding escape from the vector or partic ipating in early post-infective migration and/or development. The identific ation of an orthologue in C. elegans opens the way for further studies into the biological function(s) of this intriguing parasite product.