Mouse centric and pericentric satellite repeats form distinct functional heterochromatin

Abstract

Heterochromatin is thought to play a critical role for centromeric function. However, the respective contributions of the distinct repetitive sequences found in these regions, such as minor and major satellites in the mouse, have remained largely unsolved. We show that these centric and pericentric repeats on the chromosomes have distinct heterochromatic characteristics in the nucleus. Major satellites from different chromosomes form clusters associated with heterochromatin protein 1α, whereas minor satellites are individual entities associated with centromeric proteins. Both regions contain methylated histone H3 (Me-K9 H3) but show different micrococcal nuclease sensitivities. A dinucleosome repeating unit is found specifically associated with major satellites. These domains replicate asynchronously, and chromatid cohesion is sustained for a longer time in major satellites compared with minor satellites. Such prolonged cohesion in major satellites is lost in the absence of Suv39h histone methyltransferases. Thus, we define functionally independent centromeric subdomains, which spatio-temporal isolation is proposed to be important for centromeric cohesion and dissociation during chromosome segregation.

Granulocytic nuclear differentiation of lamin B receptor–deficient mouse EPRO cells

“…Assuming that these nuclei can be approximated to "equivalent spheres", we estimate that ic/ic nuclei have a surface area that is ~40-50% of the surface area of +/+ cells. An additional architectural difference pertaining to the DAPI-bright regions, corresponding to AT-rich pericentric heterochromatin, [26][27][28] can be observed in Figure 1. These differences were quantitated, demonstrating that the heterochromatic spots are fewer in number and larger in size in the EPRO-ic/ic cells, compared to the -+/+ and -+/ic forms (Table II).…”

Remodeling of chromatin structure in senescent cells and its potential impact on tumor suppression and aging

“…Although some mouse cells exhibit a general increase in the amount of nuclear heterochromatin as judged by histone modifications (16), senescent mouse cells have not been shown to accumulate domains of facultative heterochromatin as pronounced as the punctate SAHF observed in human cells. In mouse cells, SAHF should not be confused with the highly-condensed domains of constitutive pericentromeric heterochromatin that are present even in growing mouse cells (53). Of human cells, WI38 and IMR90 fibroblasts and primary human melanocytes form pronounced SAHF, whereas BJ fibroblasts form less marked SAHF (35,88).…”

Nucleus image properties assessed by video image analysis in mouse hepatocytes under a short lysis for extended chromatin fiber formation

“…It bears mention that enhancement in DAPI fluorescence, assumed to represent chromocenter areas known to contain centromeric and pericentromeric heterochromatin AT-rich DNA in mice (10)(11)(12), is still present in the nuclear remnants of the lysed preparations. This indicates that at least part of this centromeric/pericentromeric chromatin remained in the nuclear remnants.…”

“…Since mouse hepatocyte nuclei were analyzed here, this procedure was used just as a qualitative approach for identification of the chromocenter regions known to contain centromeric/pericentromeric AT-rich DNA (10)(11)(12) and possible changes in their distribution during ECF formation. A protocol modi-fied from Schweizer's (19) method was used.…”

“…Should a variation occurs, it could even mean that the putative structural constraint to DNA flow might be caused by differences in nuclear architecture possibly in association to differences in nuclear matrix interactions and transcriptional activities (5,8,9) in the hepatocyte nuclei. In addition, the presence of especial richness in DNA AT bases in the nuclear remnants of mouse hepatocytes could be associated with chromocenters generated by condensed centromere regions originally rich in repetitive AT-containing DNA (10)(11)(12).…”