Characteristics of cellular morphology associated with dermal knob formation in the knobbed mutant (K) of the silkworm, Bombyx mori

Larvae of the knobbed mutant (K) of the silkworm, Bombyx mori, have several paired knobs at specific sites of their dorsal segments. In the previous paper, we showed that mitoses occur in the epidermis at knob region during the prolonged period of intermolt/feeding stage. In order to clarify the process of knob formation at cellular level, morphological changes of the epidermis of knobbed region during the 4th instar were investigated by light and electron microscopy. The epidermal cells of the knobbed region were found to be more slender and taller in height than those of the non-knobbed regions, and the basal plasma membrane and attached basement membrane are irregularly distorted during the intermolt/feeding stage. At the mid-molting stage, the epidermal layer is markedly undulated and the basement membrane becomes partially detached from the basal plasma membrane. Based on these morphological characteristics together with our previous findings, the sequential process of knob formation at cellular level was discussed.