DEVELOPMENTAL ANALYSIS OF A FEMALE-SPECIFIC 16S RIBOSOMAL-RNA GENE FROM MYCETOME-ASSOCIATED ENDOSYMBIONTS OF A MEALYBUG, PLANOCOCCUS-LILACINUS

A clone showing female-specific expression was identified from an embr yonic cDNA library of a mealybug, Planococcus lilacinus, In Southern b lots this clone (P7) showed hybridization to genomic DNA of females, b ut not to that of males, However, P7 showed no hybridization to nuclei of either sex, raising the possibility that it was extrachromosomal i n origin, In sectioned adult females P7 hybridized to an abdominal org an called the mycetome. The mycetome is formed by mycetocytes, which a re polyploid cells originating from the polar bodies and cleavage nucl ei that harbour maternally transmitted, intracellular symbionts. Elect ron microscopy confirmed the presence of symbionts within the mycetocy tes, Sequence analysis showed that P7 is a 16S rRNA gene, confirming i ts prokaryotic origin, P7 transcripts are localized to one pole in you ng embryos but are found in the pole as well as in the germ band durin g later stages of development, P7 expression is detectable in young em bryos of both sexes but the absence of P7 in third instar and adult ma les suggests that this gene, and hence the endosymbionts, are subject to sex-specific elimination. Copyright (C) 1997 Elsevier Science Ltd.