Figure 6

Chromosomal location of G + C-rich bands, SSUsat and methylated regions in Spisula subtruncata. DAPI/CMA (a) followed by DAPI/PI staining (b) and FISH using the SSUsat probe (c) on the same metaphase plate and the corresponding karyotype (g) show that SSUsat signals mainly co-locate with the CMA positive, DAPI negative, G + C-rich intercalary heterochromatic regions on chromosome pairs 4, 5, 7, 8, 9, 10 and 12 and with the subterminal G + C-rich heterochromatin associated with the NOR on chromosome pair 18. Additional intercalary SSUsat signals are also present in regions not showing conspicuous CMA + /DAPI- staining in the long arms of chromosome pairs 3, 6 and 13 (asterisks in g). Immunolocalization of 5-methylcytosine (5-MeC) in the same metaphase plate (d–f) and the corresponding karyotype (g) mainly shows a homogeneous distribution of the 5-MeC signals with two main exceptions; the absolute lack of methylation signals on the biggest, intercalary CMA + /DAPI-, G + C-rich, heterochromatic, SSUsat-bearing band on the long arm of chromosome 8 (arrows in a–g) and the strong methylation showed by the subterminal NOR in one of the homologous chromosomes of pair 18. Scale bars, 5 μm.