Schistosoma mansoni: chromosomal localization of DNA repeat elements by in situ hybridization using biotinylated DNA probes.

Localization of the SM alpha family of repeated DNA and the rDNA repeat on the chromosomes of Schistosoma mansoni by in situ hybridization is presented. Biotinylated DNA was hybridized to target chromosomes and hybridization was detected using either alkaline phosphatase-labeled avidin or fluorescein-labeled avidin and biotinylated anti-avidin antibody. Hybridization detection using a fluorescein conjugate was more specific and sensitive with less background noise than detection with alkaline phosphatase conjugates. SM alpha hybridizing sequences were found dispersed throughout the genome, hybridizing to the sex chromosomes and autosomes. The SM alpha probe showed specific hybridization to the euchromatic gap region within the large heterochromatic block of the short arm of the W chromosome. This specific hybridization coupled with the lack of chiasma formation in this region of the ZW bivalent (presumably due to the heterochromatinization of this region) may explain the pattern of sex-specific hybridization reported for the SM alpha family. The rDNA repeat was localized to the secondary constriction of the short arm of chromosome 3. Specifically, the rDNA probe hybridized with the stalk of the secondary constriction and with parts of both side regions, the satellite and the short arm proper.