Organisation of complex nuclear domains in somatic mouse cells

The number and associations of heterochromatin chromocenters, nucleoli, cen tromeres and telomeres were studied in the nucleus of different somatic cel ls of Mus domesticus. Fibroblasts of the cell line 3T3, kidney cells (prima ry culture), and bone marrow cells were used. The above mentioned nuclear a nd chromosome markers were identified by DAPI/actinomycin D, indirect immun ofluorescence with anti-centromere antibodies, silver impregnation for nucl eolar proteins and fluorescence in situ hybridisation (FISH) with telomeric probes. The quantitative analysis of the nuclei showed that the pericentro meric heterochromatin is organised in about 18 chromocenters per nucleus in the 3T3 cells, and about seven in kidney and bone marrow cells, having gen erally a peripheral distribution in the nucleus of all the studied cells. S everal aggregated centromeres were participating in each of the chromocente rs, about four centromeres per 3T3 cell and about six centromeres per kidne y and bone marrow cells. Some of the chromocenters were also in close assoc iation with nucleoli. The number of telomeric labels per nucleus was as exp ected for each chromosome set (2n = 68-70 and 2n = 40). About half of the t elomeric signals were loosely aggregated within the heterochromatic blocks while the rest were distributed in the nucleus as unrelated units not bound with chromocenters. The three cell types have complex nuclear territories formed by different chromosomal domains: the pericentromeric heterochromati n, centromeres, proximal telomeres and nucleoli. With the exception of some bone marrow cells, we have not found a nuclear polarisation of the analyse d chromosomal markers compatible with the Rab1 configuration. However, Rab1 anaphasic polarisation allows the contact of centromeric regions making po ssible that centromeric associations arise. If in addition, associative ele ments much as constitutive heterochromatin or nucleoli are close to the cen tromeric regions, like in Mus domesticus chromosomes, then the associations might be consolidated and persist until the interphase. These associations may be the origin of the nuclear domains described here for Mus domesticus somatic cells. (C) Elsevier, Paris.