PUTATIVE PROTAMINES, SPCH-1/2/3, PLAY A ROLE IN FERTILITY
Jennifer Gilbert, Diana Chu.
San Francisco State University, San Francisco, CA.
Male infertility is a significant medical concern for millions around the world. A major cause of male infertility is the improper compaction of sperm chromatin during spermatogenesis. Small proteins called protamines facilitate this compaction, yet their protein to protein interactions and exact contribution to fertility is unknown. Protamine identification and study is complicated by the fact they exhibit high sequence variability, resulting in little to no homology across species. Proteomic analysis identified 3 novel proteins, SPCH-1/2/3, enriched in the sperm chromatin of C. elegans. We hypothesize that SPCH-1/2/3 are C. elegans protamines that contribute to fertility through proper DNA compaction. Despite the high level of identity between SPCH-1/2/3 (88 - 99%), spch-2 mutants produce progeny at only 33% of wild type, while spch-1 and spch-3 counts are similar to wild type. Further, spch-3,spch-1 double mutants do not show reduced progeny numbers. These findings suggest that SPCH-2 contributes to fertility. SPCH proteins likely contribute to fertility through compaction and packaging of sperm DNA. Antibody staining of fixed male germlines reveals SPCH localization around the condensed nuclei of mature sperm. Further, SPCH-1/2/3 are removed immediately after fertilization as the paternal pronucleus decondenses. Interestingly, mass spec analysis shows that SPCH-1/2/3 are highly phosphorylated (82 - 88%) at sites that differentiate between SPCH-1 and SPCH-2/3. This may be part of a mechanism for the cell machinery to distinguish between the 3 SPCH proteins. Removing the sites of differential phosphorylation using CRISPR will provide further evidence for the function of this modification.