Schistosoma mansoni: chromosomal localization of female-specific genes and a female-specific DNA element

Two genes, p14 and p48, that are each expressed in a female-specific manner in vitelline cells in response to male pairing were each localized by in situ hybridization to chromosome 2. Biotinylated DNA was hybridized to target chromosomes and hybridization was detected using either alkaline phosphatase-labeled avidin or fluorescein-labeled avidin. In addition Southern blots of genomic DNA separated by pulsed-field gradient gel electrophoresis was used to localize the genes to large chromosome fragments. p14 was localized to two EagI fragments (150 and 240 kb) found in the distal portion of the lower (q) arm of chromosome 2 in 79 of 109 metaphase preparations examined. p48 was localized to two EagI fragments (50 and 700 kb) found in the proximal portion of the lower arm of chromosome 2 in 52 of 63 metaphase preparations examined. A DNA repeat element, pW1, that hybridizes to genomic DNA from female but not male Schistosoma mansoni was also used as a hybridization probe. In all cells examined the biotinylated pW1 only hybridizes to a euchromatic gap region (eg3) within the large heterochromatin block of the long 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 heterochromatization) is offered as an explanation for the female-specific hybridization of pW1.