In praise of mealybugs.

The fascinating chromosomal cycle leading to facultative heterochromatization in the mealybugs has been a challenging system for mechanistic understanding of the phenomenon of genomic imprinting and epigenetics. The elegant cytological dissection of the various processes reported in the literature is equally fascinating for the researchers of current molecular age. Presently, a two way approach is being pursued; continued efforts of utilizing elegant cytology, in combination with the molecular probes to decipher molecular correlates on one hand and on the other, the de novo biochemical/molecular analysis for the identification of the molecular players using genomic tools. The hope is to uncover novel players in genomic imprinting and epigenetic regulation in the mealybug system which shows differential regulation of the entire genome, with 50% of its genome being transcriptionally inactivated in a parental-origin-specific and sex specific manner. In addition to being a model for epigenetic regulation, the mealybugs are being utilized for the analysis of radiation resistance as well as metabolic interactions between the microbiome and the host. The overview presented here is an attempt to bring out some of the work carried out in these directions. We also discuss the areas that remain poorly explored in this system, such as the role/involvement of noncoding RNA in male-specific inactivation and the molecular dissection of heterochromatin, the cytological manifestation of the inactive state of genes and chromosome.