Chromosomal localization of 18S rDNA and telomere sequence in the aye-aye,Daubentonia madagascariensis

Chromosomal localization of 18S rDNA and telomere sequence was attempted on the chromosomes of the aye-aye (2n = 30) using fluorescence in situ hybrid ization (FISH) and primed in situ labeling (PRINS), respectively. The rDNA was localized at the tip or whole of the short arm of acrocentric chromosom es 13 and 14 in all spreads observed. However, post-FISH silver-nitrate (Ag ) staining showed that transcriptional activity of the rRNA genes was varia ble, particularly in chromosome 14, which was most frequently negative in o ne homologue carrying the smaller copy number of rDNA. This observation sup ports, at the molecular cytogenetic level, previous data concerning the rel ationship between the copy number of rDNA and its trancriptional activity. On the other hand, telomere sequence was localized only at the telomeric re gion of all chromosomes, the so-called telomere-only pattern, a characteris tic similar to that of the greater bushbaby. These data may provide informa tion on the chromosomal evolution of the lemur, because locations of rDNA a nd telomere sequences frequently offer important clues in reconstruction of karyotype differentiation.