Germ cells carry the hereditary information that is passed across generations and therefore their genome must be safeguarded from invasive genetic materials like viral DNA, transposons, etc. Hence, the germ cells employ special surveillance machinery. Mutants of the genes involved in this silencing pathway express transposons—and even some transgenes, which are otherwise silenced—in their germlines. Small RNAs and the Argonaute proteins form the major workforce of this silencing machinery.
The free-living, soil nematode Caenorhabditis elegans is one of the established model organisms to study germ cell development. Our laboratory focuses on how PUF-8(Pumilio/FBF) domain-containing), a highly-conserved RNA-binding protein, contributes to germ cell development in the C. elegans germ line. Linitha Thomas, a former graduate student, studied the genetic interaction between PUF-8 and PLP-1 (Pur-alpha Like Protein-1), the C. elegans ortholog of the mammalian Pur-alpha. The orthologs of PLP-1 have been shown to bind nucleic acids, and interact with proteins in other species. Genetic interaction with PUF-8 and presence of nucleic acid-binding domains motivated me to study further about PLP-1 in germ cell development.
My thesis work identified plp-1 to function as a part of the gene silencing machinery, as single-copy integrated transgenes, extrachromosomal array transgenes, and the piRNA sensors are desilenced in plp-1 mutant germlines. Further, I observed that plp-1 participates at the initiation of gene silencing, without being required for the biogenesis of any of the small RNAs. Furthermore, plp-1 mutants display temperature-dependent sterility, similar to many mutants that have impaired germline gene-silencing machinery. My analysis on the transcriptome of plp-1 mutant worms showed that several endogenous, protein-coding genes are misexpressed in their germlines, with a significant number of them common to those upregulated in prg-1 and mut-16 mutants. In summary, I find that plp-1 functions at the initiation step of the germline gene-silencing pathway; most likely downstream of small RNA biogenesis.
Publication:
Vishnupriya, R., L. Thomas, L. Wahba, A. Fire and K. Subramaniam (2020). PLP-1 is essential for germ cell development and germline gene silencing in Caenorhabditis elegans. Development 147, dev195578.