Plant & Animal Genomes XI Conference Plant & Animal Genomes XI ConferenceJanuary 11-15, 2003
Town & Country Convention Center
San Diego, CA
Poster: Cytology, in situ and microcloning
The heterochromatin has been reported as an important component in the chromosome differentiation of several groups of fish. The genus Hisonotus represent a good model for heterochromatin studies, since the amount and distribution patterns of heterochromatin are highly diversified among the species. The species of this genus can be separated in two groups: the first one (i) with a few amount of heterochromatin is represented by H. nigricauda, H. sp. A and H. sp. D, and the second one (ii) with a large amount of heterochromatin is represented by H. leucofrenatus. In order to address the role of heterochromatin in the genome evolution in fish, cytogenetic and molecular studies were carried out in H. leucofrenatus. The heterochromatin of H. leucofrenatus is distributed on terminal position in five chromosome pairs. However, it was detected a variation in the distribution of these heterochromatic blocks among the analyzed specimens. This heterochromatic portion was strongly stained with the fluorochrome DAPI, suggesting an AT-rich composition. On the other hand, those regions were also stained by the fluorochrome Chromomycin A3, suggesting the existence of CG-rich DNA segments. A 90 base pair satellite sequence isolated from this species presented 61% of AT and its localization was coincidence with the heterochromatic blocks. The chromosome distribution of this satellite DNA was not homogeneous over the heterochromatic segments, showing the presence of small clusters separated by unstained DNA segments, corroborating the results obtained with the fluorochromes. Southern blot experiments showed that this satellite sequence is specific to H. leucofrenatus species, which suggest that this sequence may have had an important role in the process of chromosome differentiation, at least at population level, in this species.