Sex-specific organisation of middle repetitive DNA sequences in the mealybug Planococcus lilacinus

Differential organisation of homologous chromosomes is related to both sex determination and genomic imprinting in coccid insects, the mealybugs. We r eport here the identification of two middle repetitive sequences that are d ifferentially organised between the two sexes and also within the same dipl oid nucleus. These two sequences form a part of the male-specific nuclease- resistant chromatin (NRC) fraction of a mealybug Planococcus lilacinus. To understand the phenomenon of differential organisation we have analysed the components of NRC by cloning the DNA sequences present, deciphering their primary sequence, nucleosomal organisation, genomic distribution and cytolo gical localisation, Our observations suggest that the middle repetitive seq uences within NRC are functionally significant and we discuss their probabl e involvement in male-specific chromatin organisation.