540B Poster - 07. Chromatin, epigenetics and genomics
Friday April 08, 2:00 PM - 4:00 PM

Authors:
Alyssa Slicko ^1,2; Jonathan Nelson ¹; Yukiko Yamashita ^1,2,3

Affiliations:
1) Whitehead Institute, Cambridge, MA; 2) Howard Hughes Medical Institute; 3) Department of Biology, MIT, Cambridge, MA

Keywords:
e. heterochromatin; b. germline stem cell

An important role of the germline is to maintain unstable, but essential genomic elements to ensure the transmission of functional genomes across generations. Among these elements are ribosomal DNA (rDNA), which consists of hundreds of tandem repeats of the genes that are needed for sufficient ribosomal activity. rDNA is known to be one of the most unstable regions in the genome because this repetitive structure is susceptible to deleterious recombination. This instability is countered in the germline to prevent the progressive multi-generational loss of rDNA, but the mechanisms that underlie this feature have remained unknown. Our previous work suggests that rDNA is maintained by copy number expansion in the germline that recovers copies lost in the previous generation, though the factors that achieve this expansion remain largely unknown. Here we describe our efforts to identify these factors through RNAi-mediated knockdown of candidate genes.

We used a well-described system of robust rDNA copy number expansion in the male germline called “rDNA magnification” to identify factors required for rDNA expansion. Previous work revealed that animals with very little rDNA, meaning no rDNA on Y and partial rDNA on X, have the bobbed phenotype, which displays disrupted dorsal cuticle patterning. rDNA magnification is the phenomenon that a small amount of offspring from bobbed males have wild-type cuticles due to the rDNA on the partially deleted X chromosome having been expanded. We tested the ability for RNAi knockdown of candidate genes to prevent rDNA magnification in bobbed males.

We selected candidate factors of known rDNA-binding proteins, and homologs of factors that aid in rDNA maintenance in yeast, to test with the RNAi. We preliminarily identified that an uncharacterized gene on the Y chromosome, PRY (Polycystine-related Y), contributes to rDNA magnification. PRY was tested as a candidate factor since it resides in a portion of the Y chromosome previously identified to be necessary for rDNA magnification. We discovered that the transgenic expression of PRY can induce rDNA magnification in both the male and female germline. We are now investigating the activity of PRY in the germline to understand how it contributes to rDNA magnification.