Human CBX5 ELISA Matched Antibody Pair

Telomeres are capping structures at the ends of eukaryotic chromosomes composed of TTAGGG repeats bound to an array of specialized proteins(1-3). Telomeres are heterochromatic regions. Yeast and flies with defects in activities that modify the state of chromatin also have abnormal telomere function(4-6), but the putative role of chromatin-modifying activities in regulating telomeres in mammals is unknown. Here we report on telomere length and function in mice null with respect to both the histone methyltransferases (HMTases) Suv39h1 and Suv39h2 (called SUV39DN mice). Suv39h1 and Suv39h2 govern methylation of histone H3 Lys9 (H3-Lys9) in heterochromatic regions(7). We show that primary cells derived from SUV39DN mice have abnormally long telomeres relative to wild-type controls. Using chromatin immunoprecipitation (ChIP) analysis, we found that telomeres were enriched in di- and trimethylated H3-Lys9 but that telomeres of SUV39DN cells had less dimethylated and trimethylated H3-Lys9 but more monomethylated H3-Lys9. Concomitant with the decrease in H3-Lys9 methylation, telomeres in SUV39DN cells had reduced binding of the chromobox proteins Cbx1, Cbx3 and Cbx5, homologs of Drosophila melanogaster heterochromatin protein 1 (HP1). These findings indicate substantial changes in the state of telomeric heterochromatin in SUV39DN cells, which are associated with abnormal telomere elongation. Taken together, the results indicate epigenetic regulation of telomere length in mammals by Suv39h1 and Suv39h2.

Mammals have three HP1 protein isotypes HP1 beta (CBX1), HPl gamma (CBX3) and HP1 alpha (CBX5) that are encoded by the corresponding genes Cbx1, Cbx3 and Cbx5. Recent work has shown that reduction of CBX3 protein in homozygotes for a hypomorphic allele (Cbx3(hypo)) causes a severe postnatal mortality with around 99% of the homozygotes dying before weaning. It is not known what the causes of the postnatal mortality are. Here we show that Cbx3(hypo/hypo) conceptuses are significantly reduced in size and the placentas exhibit a haplo-insufficiency. Late gestation Cbx3(hypo/hypo) placentas have reduced mRNA transcripts for genes involved in growth regulation, amino acid and glucose transport. Blood vessels within the Cbx3(hypo/hypo) placental labyrinth are narrower than wild-type. Newborn Cbx3(hypo/hypo) pups are hypoglycemic, the livers are depleted of glycogen reserves and there is almost complete loss of stored lipid in brown adipose tissue (BAT). There is a 10-fold reduction in expression of the BAT-specific Ucp1 gene, whose product is responsible for non-shivering themogenesis. We suggest that it is the small size of the ChX3(hypo/hypo) neonates, a likely consequence of placental growth and transport defects, combined with a possible inability to thermoregulate that causes the severe postnatal mortality.