An Unusually Simple HP1 Gene Set in Hymenopteran Insects

The heterochromatin protein 1 (HP1) gene family includes a set of paralogs in higher eukaryotes that serve fundamental roles in heterochromatin structure and maintenance, and other chromatin-related functions. At least ten full and sixteen partial HP1 genes exist among Drosophila species, with multiple gene gains, losses and sub-functionalizations within this insect group. An important question is whether this diverse set of HP1 genes and their dynamic evolution represent the standard rule in eukaryotic groups. Here we have begun to address this question by bioinformatically identifying the HP1 family genes in representative species of the insect order Hymenoptera, which includes all ants, bees, wasps and sawflies. Compared to Drosophila species, hymenopterans have a much simpler set of HP1 genes, including one full and two partial HP1s. All three genes appear to have been present in the common ancestor of the hymenopterans and they derive from a Drosophila HP1B-like gene. In ants, a partial HP1 gene containing only a chromoshadow domain harbors amino acid changes at highly conserved sites within the PxVxL recognition region, suggesting that this gene has undergone sub-functionalization. In the jewel wasp Nasonia vitripennis the full HP1 and partial chromoshadow-only HP1 are expressed in both germ line and somatic tissues. However, the partial chromodomain-only HP1 is expressed exclusively in the ovary and testis, suggesting that it may have a specialized chromatin role during gametogenesis. Our findings demonstrate that the HP1 gene family is much simpler and evolutionarily less dynamic within the hymenopterans compared to the much younger Drosophila group, a pattern that may reflect major differences in the range of chromatin-related functions present in these and perhaps other insect groups.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author