Chromosomal location of major ribosomal genes (18S5.8S28S rDNA) and (TTAGGG)n telomeric sequences has been investigated for the first time in pipefish (Syngnathidae) by application of fluorescence in situ hybridization (FISH). Two species were studied: Nerophis ophidion (L.) (2n karyotype = 58 metacentric, submetacentric and subtelocentric chromosomes)and Syngnathus abaster Risso (2n karyotype =44 acrocentric chromosomes) (Vitturi et al. 1998). The results indicate that in both pipefishes intraspecific numerical variation of ribosomal sites is more conspicuous than previously detected (Vitturi et al. 1998). (TTAGGG)n FISH showed a regular hybridization pattern in S. abaster, while in N. ophidion it gave unexpected enlarged hybridization signals in the terminal region of either two or five chromosomes, where telomeric sequences were interspersed throughout nucleolus organizer regions NORs (interstitial telomeric sites, ITS). Diversification of ribosomal and telomeric repeats in the karyotype of the two species confirms the hypothesis that the genera Nerophis and Syngnathus have undergone two different pathways of karyotypic evolution. The teleostean family Syngnathidae (pipefish and seahorses)includes 277 species, of which 11 inhabit the Mediterranean Sea and belong to the genera Nerophis (two species), Hippocampus (two species), Minyichthys (one species) and Syngnathus (six species) (FishBase 2005). Owing to the difficulty in obtaining high-quality chromosome preparations, cytogenetic data on syngnathids are scanty, referring in literature only to five Mediterranean species (two seahorses and three pipefishes), and are restricted to only a few aspects, including diploid chromosome number, karyotypic macrostructure, location of active NORs by silver staining, and genome size (Vitturi et al. 1998). With regard to NOR location, staining with silver nitrate and the fluorochrome chromomycin A3 (CMA3) has been widely applied to metaphase plates of both vertebrates and invertebrates to detect number and position of active NORs and GC-rich NORs, respectively (Sumner 1990, and references therein). However, both methods have proven to be inadequate in unequivocally characterizing the ribosomal pattern (active and inactive rDNA genes) in the karyotype of several species. It has been shown that molecular techniques provide additional opportunities for animal cytogenetics.Gasteroisteiformes and its family Syngnathidae. In this note we report the first attempt to apply FISH to pipefish chromosomes.
FISH mapping of 18S rDNA and (TTAGGG)(n) sequences in two pipefish species (Gasteroisteiformes : Syngnathidae).
Libertini A;
2006
Abstract
Chromosomal location of major ribosomal genes (18S5.8S28S rDNA) and (TTAGGG)n telomeric sequences has been investigated for the first time in pipefish (Syngnathidae) by application of fluorescence in situ hybridization (FISH). Two species were studied: Nerophis ophidion (L.) (2n karyotype = 58 metacentric, submetacentric and subtelocentric chromosomes)and Syngnathus abaster Risso (2n karyotype =44 acrocentric chromosomes) (Vitturi et al. 1998). The results indicate that in both pipefishes intraspecific numerical variation of ribosomal sites is more conspicuous than previously detected (Vitturi et al. 1998). (TTAGGG)n FISH showed a regular hybridization pattern in S. abaster, while in N. ophidion it gave unexpected enlarged hybridization signals in the terminal region of either two or five chromosomes, where telomeric sequences were interspersed throughout nucleolus organizer regions NORs (interstitial telomeric sites, ITS). Diversification of ribosomal and telomeric repeats in the karyotype of the two species confirms the hypothesis that the genera Nerophis and Syngnathus have undergone two different pathways of karyotypic evolution. The teleostean family Syngnathidae (pipefish and seahorses)includes 277 species, of which 11 inhabit the Mediterranean Sea and belong to the genera Nerophis (two species), Hippocampus (two species), Minyichthys (one species) and Syngnathus (six species) (FishBase 2005). Owing to the difficulty in obtaining high-quality chromosome preparations, cytogenetic data on syngnathids are scanty, referring in literature only to five Mediterranean species (two seahorses and three pipefishes), and are restricted to only a few aspects, including diploid chromosome number, karyotypic macrostructure, location of active NORs by silver staining, and genome size (Vitturi et al. 1998). With regard to NOR location, staining with silver nitrate and the fluorochrome chromomycin A3 (CMA3) has been widely applied to metaphase plates of both vertebrates and invertebrates to detect number and position of active NORs and GC-rich NORs, respectively (Sumner 1990, and references therein). However, both methods have proven to be inadequate in unequivocally characterizing the ribosomal pattern (active and inactive rDNA genes) in the karyotype of several species. It has been shown that molecular techniques provide additional opportunities for animal cytogenetics.Gasteroisteiformes and its family Syngnathidae. In this note we report the first attempt to apply FISH to pipefish chromosomes.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
