Isolation and characterization of Suv39h2, a second histone H3 methyltransferase gene that displays testis-specific expression

Higher-order chromatin has been implicated in epigenetic gene control and i n the functional organization of chromosomes. We have recently discovered m ouse (Suv39h1) and human (SW39H1) histone H3 lysine 9-selective methyltrans ferases (Suv39h HMTases) and shown that they modulate chromatin dynamics in somatic cells. We describe here the isolation, chromosomal assignment, and characterization of a second murine gene, Suv39h2. Like Suv39h1, SIlv39h2 encodes an H3 HMTase that shares 59% identity with Suv39h1 but which differ s by the presence of a highly basic N terminus. Using fluorescent in situ h ybridization and haplotype analysis, the Suv39h2 locus was mapped to the su bcentromeric region of mouse chromosome 2, whereas the Suv39h1 locus reside s at the tip of the mouse X chromosome. Notably, although both Suv39h loci display overlapping expression profiles during mouse embryogenesis, Suv39h2 transcripts remain specifically expressed in adult testes. Immunolocalizat ion of Suv39h2 protein during spermatogenesis indicates enriched distributi on at the heterochromatin from the leptotene to the round spermatid stage. Moreover, Suv39h2 specifically accumulates with chromatin of the sex chromo somes (XY body) which undergo transcriptional silencing during the first me iotic prophase. These data are consistent with redundant enzymatic roles fo r Suv39h1 and Suv39h2 during mouse development and suggest an additional fu nction of the Suv39h2 HMTase in organizing meiotic heterochromatin that may even impart an epigenetic imprint to the male germ line.