title: opossum #2 round spermatid H3K4me3 ChIP
design: Testes from Monodelphis domestica were obtained from animals culled from a colony maintained at the Texas Biomedical Research Institute. Populations of pachytene spermatocytes and round spermatids (purity 89-90%) were recovered using a StaPut gradient as previously described (Bellve et al, 1993).  Cells were washed once in PBS and then split into two aliquots.  One aliquot (for ChIP) was fixed in 1% formaldehyde then quenched with 2.5M glycine, while the second (for RNA) was left unfixed.  Both fixed and unfixed aliquots were snap frozen in liquid nitrogen, then stored at -80C.  ChIP was performed as previously described (Lesch et al 2013).  ChIP-seq libraries were prepared using a TruSeq ChIP sample prep kit (Illumina) according to the manufacturer’s instructions, except that size selection was performed after instead of before PCR amplification.