SPARC preserves follicular epithelium integrity in insect ovaries

The importance of juvenile hormone regulating insect oogenesis suggests looking for genes whose expression is regulated by this hormone. SPARC is a calcium-binding glycoprotein that forms part of the extracellular membranes, which in vertebrates participates in bones mineralization or regulating cell proliferation in some cancer types. This large number of functions described for SPARC in different species might be related to the significant differences in its structure observed when comparing different species-groups. Indeed, these structural differences allow characterizing the different clades. In the cockroach Blattella germanica, a SPARC homolog emerged from ovarian transcriptomes that were constructed to find genes responding to juvenile hormone. In insects, SPARC functions have been studied in oogenesis and in embryo development of Drosophila melanogaster. In the present work, using RNAi approaches, novel functions for SPARC in the B. germanica panoistic ovaries are described. We found that depletion of SPARC does not allow to the follicular cells to complete mitosis, resulting in giant follicular cells nuclei and in a great alteration of the ovarian follicle cytoskeleton. The SPARC contribution to B. germanica oogenesis occurs stabilizing the follicular cell program and helping to maintain the nuclear divisions. Moreover, SPARC is necessary to maintain the cytoskeleton of the follicular cells. Any modification of these key processes disables females for oviposition.