DIFFERENTIAL EXPRESSION OF MESSENGER-RNAS FOR M31 AND M32, MURINE HOMOLOGS OF DROSOPHILA HETEROCHROMATIN PROTEIN-1 (HP1), DURING MURINE EMBRYOGENESIS

Mice have two structural homologues of the Drosophila HP1 gene, termed M31 and M32, which have two structurally conserved domains, the chrom e (C) and chrome shadow (CS) domains. In Drosophila, HP1 has been isol ated as one of the components of conserved chromatin structure (hetero chromatin) and is thought to bind DNA indirectly by mediating formatio n of a complex of nuclear proteins. However, little is known about the function of M31 and M32 in mammals. In order to assess the function o f the M31 and M32 proteins, Northern blot analysis was performed in mi ce. M32 mRNA (with approximately 1,800 nucleotides (ntds)) was express ed strongly throughout embryonic stages examined and in TT2 embryonic stem (ES) cells, while expression of M31 mRNA (with approximately 2,30 0 and 1,100 ntds) was strong in embryos at embryonic day 8.5 (E8.5) an d in TT2 cells, but was decreased at E12.5 and thereafter. Tn adults, expression of M32 mRNA was strongest in brain and brain stem among tis sues examined, and was relatively weak in organs including kidney, sto mach, intestine and testis. The two M31 transcripts were weakly but un iformly expressed throughout the organs examined in adults. These find ings suggest that M31 and M32 may play different roles in murine embry ogenesis, although they have the C and CS domains and are members of t he same gene family.