Expression profiling of homeobox genes in silk gland development in the mulberry silkworm Bombyx mori

The homeobox (Hox) genes constitute an evolutionarily conserved family encoding transcription factors which play major roles in segmental identity and organ specification, across species. The expression patterns of three Hox genes, Antennapedia (Antp), Ultrabithorax (Ubx) and even-skipped (eve) were analyzed during silk gland development in Bombyx mori. Antp followed a middle silk gland (MSG) restricted pattern of expression, whereas Ubx was specifically expressed in the posterior silk gland (PSG) during embryonic and larval developmental stages. Eve protein, on the other hand, was expressed in both MSG and PSG. We have also identified and characterized a novel Pax-like mRNA that is expressed exclusively in the PSGs during embryonic and larval development. The expression of Antp, Ubx and Pax-like reached maximum levels in the fifth larval intermoult and no expression was detected during the intervening moults. The region-specific expression of certain Hox genes appears to be responsible for the specification of silk gland compartments, whereas other Hox genes may play a global role in controlling the expression of genes encoding silk proteins.