Ribosomal RNA genes in mosquitoes: localization by fluorescence in situ hybridization (FISH)

Abstract

Fluorescence in situ hybridization (FISH) was used to localize the 18S-28S ribosomal RNA gene clusters on the chromosomes of 15 mosquito species belonging to the Anophelinae and Culicinae subfamilies. In the genus Anopheles the rRNA genes are localized on the heterochromatic arm of both sex chromosomes. The association between rRNA genes and sex determining chromosomes also applies to the homomorphic karyotype of Culicinae mosquitoes, at least in those cases in which localization of the sex locus/loci has been determined. In these species ribosomal genes are often found within or adjacent to heterochromatic regions (C bands). Differences in the location of rRNA genes among and within genera suggest the occurrence of several chromosomal rearrangements during the evolution of mosquitoes.

Location of ribosomal genes in the chromosomes of Anopheles darlingi and Anopheles nuneztovari (Diptera, Culicidae) from the Brazilian Amazon

“…The 4C band is associated with the nucleolus through fibers and grains that can be seen extending from the band into the nucleolus. This association may be related to the transcriptional activity in the NOR (Marchi & Pili 1994). A similar pattern of hybridization was observed in A. darlingi from Novo Airão, Manaus and Macapá, and A. nuneztovari from Manaus and Macapá.…”

“…In 20 species of mosquitoes belonging to eight genera of the subfamily Culicinae, the rDNA was located on a single mitotic chromosome which had rRNA genes dispersed along the length of all three pairs of theese chromosomes (Kumar & Rai 1990. In contrast, in A. petragnani, A. hispaniola (Marchi & Pili 1994), A. gambiae (Kumar & Collins 1994) and A. stephensi (Redfern 1981), the rRNA genes were located on the sex pairs, mainly within heterochromatic regions (C-banding) or adjacent to them.…”

“…As in individuals with different rDNA amounts detected in populations of Anopheles, Culex, Aedes and Orthopodomyia (Marchi & Pili 1994), the oriental Anopheles species are prone to variations in the content of constitutive heterochromatin in their mitotic chromosomes, especially in the sex pairs with consequent differences in size and shape (Baimai et al 1996, Baimai 1998. In dipteran insects, constitutive heterochromatin may account for more than 60% of the length of the X chromosome (Baimai 1998).…”

“…arizonensis complex (Bicudo 1982), Ceratitis capitata (Bedo & Webb 1989), Sciara ocellaris (Dessen & Perondini 1991), and the blow flies Chrysomyia megacephala and C. putoria (Parise-Maltempi & Avancini 2001). In mosquitoes, the rRNA genes are located within and around the heterochromatic regions, especially on the sex chromosomes in the subfamily Culicinae and in some species of the subfamily Anophelinae (Marchi & Pili 1994). However, there are no in situ hybridization studies for A. darlingi and A. nuneztovari (both in the subgenus Nyssorhynchus).…”

Internal Repetition and Intraindividual Variation in the rDNA ITS1 of the Anopheles punctulatus Group (Diptera: Culicidae): Multiple Units and Rates of Turnover

“…punctulatus group. The presence of the rDNA on the heterologous X and Y chromosomes in Anopheles (Marchi and Pili 1994) enabled an analysis of interindividual differences through a comparison of variation between the sexes. The An.…”