Developmental expression of the Bombyx Antennapedia homologue and homeotic changes in the Nc mutant

Abundant availability of homeotic mutants in Bombyx mori provides us with clues to study the body plan of the silkworm. Previous studies indicated that the ECa/ECa and EN/EN embryos, which reveal drastic morphological changes (Itikawa 1943, 1952) lack the homologue of abd-A and the homologues of abd-A and Ubx, respectively (Ueno et al. 1992). It will be interesting to characterize a mutant named Nc, the locus of which was mapped about 1.4 cm apart from the E loci (Itikawa 1944, 1952).

In the present study we cloned and identified the Bombyx Antennapedia cDNA from a library of larval middle silk gland. The developmental expression patterns of the Bombyx Antennapedia were analysed in embryos and larval middle silk glands. We found the Bombyx Antennapedia mRNA of the Nc mutant lacks the homeobox region and its downstream region. This defect comes from a corresponding deletion on the Nc chromosome. Development of the Nc/Nc embryos terminates at stage 26, revealing a transformation of the prothoracic legs into antennae, milder changes in the mesothoracic legs, compression between the prothoracic and mesothoracic segments as well as in the gnathocephalon region, and a severe growth suppression of the silk glands.

These results give a molecular basis and detailed morphological abnormalities of the Nc mutant known since 1944.