The Problem of Sex Chromosomes in Polytene Tissues of Anastrepha fraterculus.

GIARDINI, M.CECILIA; MILLA, F; LANZAVECCHIA, S; NIEVES, MARIELA; CLADERA, J.

Bangkok

Congreso; 9th. International Symposium on Fruit Flies of Economic Importance (ISFFEI); 2014

Background: Polytene chromosome characterization is very important for the analysis of nuclear genome organization, phylogenetic studies and genetic mapping.Anastrepha fraterculus Wied (Diptera, Tephritidae) (2n=10+XX/XY) flies have polytene chromosomes in their salivary glands. We found five polytene elements, corresponding to the five autosomes. We infer that X and Y chromosomes are heterochromatic and do not form banded polytene elements. The same situation has been observed in several other tephritid species. From the analysis of the spatial and linear map of the polytenized chromosomes of A. fraterculus, we intend to confirm whether sexual chromosomes suffer polytinization as well as the autosomes.Methods: Salivary glands from A. fraterculus third instar larvae were removed, treated according to Ashburner (1989) with modifications, and examined under microscope. In order to confirm the non-polytinization of sex chromosomes we carried out FISH (Fluorescent in situ Hibridization) analysis, following Fantini et al. (2011), with modifications, using 18S rDNA genes as probe, as these genes are harbored by the sex chromosome in this species. Results: Using the 18S probe, we identified a positive signal in an uncondensed heterochromatic region that corresponds to the non-polytenized sexual chromosomes, FISH analysis previously demonstrated that in mitotic tissues this probe hybridizes only in sex chromosomes. Besides we labeled chromosomes from II to VI according to their size following the Bridges´ system. So far, it has not been possible to establish the equivalence between mitotic and polytene chromosomes. We did not observe a typical chromocentre, resulting in the separation of the individual chromosomes and we observed the presence of the nucleolus in the analyzed cells.Conclusions: We identified the five politenized autosomes of A. fraterculus and confirm the presence in a non-polytenized form of its sex chromosomes. We are working on a complete chromosome map to use this important tool to clarify the complexity displayed by A. fraterculus.Key words: Anastrepha fraterculus, sex chromosomes, polytene chromosomes, salivary glands, map.