Inhibition of abnormal proliferation of epidermal cells in the knobbed mutant silkworm larva by the heavy-ion microbeam irradiation

Abstract

Silkworm is an experimental insect good to investigate developmental biology or cell differentiation. About 400 silkworm strains are collected and maintained, especially larval pigmentation mutations or morphotypes are mainly stored. One of them, termed Knobbed (K) mutant is a quite unique and important model of cell differentiation, in that cells in the knob region consist of abnormally proliferated and stratified cells.
In this study, the new application of irradiation with heavy ion microbeam for the first instar silkworm larvae was developed to clarify that when and where the knob mutant would form by suppressed proliferation of epidermal cells. The holed aluminum plates were specially designed to fix the first instar larvae of silkworm during irradiation. After irradiation with 180-μm-diameter microbeam of 220 MeV ¹²C ions, larvae were reared to evaluate the accuracy of irradiation. The deletion of knob was observed in over 70% of the larvae at fifth instar (LET=127.9 MeV/μm ions, where the absorbed dose of epidermal cells are equivalent to 500 Gy). The epidermal cells stayed as it was a monolayer at irradiated region. These results indicate that heavy ion beam irradiation can control the abnormal cell division of epidermis in the knob mutant.