One key contributor to male fertility is the proper packaging of DNA in sperm. This packaging is facilitated by histones, which compact DNA and manage the accessibility of DNA for transcription. Histone variants are specialized in function and replace canonical histones. For example, the histone H2A variant HTZ-1 is 54% identical to H2A, expressed in all cell types, and present at 23% of all C. elegans promoters, which suggests a role in transcription1. HTAS-1 is 48% identical to H2A and incorporated into sperm chroamtin during a period of global transcriptional silencing. Because both variants are expressed during spermatogenesis, our goal is to understand how the incorporation of HTZ-1 and HTAS-1 may influence gene transcription during sperm formation. We hypothesize that while HTZ-1 will be incorporated at active chromatin in the male germ line, HTAS-1 may be incorporated at repressed chromatin. To test this, we have conducted immunlocalization of HTZ-1 and HTAS-1 during spermatogenesis. First, we found that HTAS-1 and HTZ-1 co-localize during later stages of spermatogenesis and both are under-represented on the X transcriptionally-silent chromosome. This suggests, counter to our original hypothesis, that HTZ-1 and HTAS-1 may both be incorporated in transcriptionally active chromatin. To further assess this, we will test whether HTZ-1 and HTAS-1 are located on active or inactive extrachromosomal arrays in males. Preliminary data has shown that HTZ-1 is localized on active arrays in the hermaphrodite germ line; thus we anticipate that HTZ-1 will also colocalize to transcriptionally active arrays in males. Immunolocalization of HTAS-1 to active and inactive arrays is also currently underway. Further, because HTAS-1 and HTZ-1 differ from H2A in their N- and C-termini, we will create chimeras by swapping these domains onto canonical H2A and analyze their localization to transcriptionally active or inactive sites. We expect that this research will correlate HTZ-1 and HTAS-1 incorporation with transcription and define important features of H2A variant structure required for their potential roles in transcriptional regulation.

Affiliation:
- San Francisco State University , San Francisco , CA.