Epidermal mitotic activity associated with knob formation in the 'Knobbed' mutant of the silkworm, Bombyx mori
2009
Shimura, S., National Inst. of Agrobiological Sciences, Tsukuba, Ibaraki (Japan) | Kiuchi, M. | Kiguchi, K.
The knobbed mutant of the silkworm, Bombyx mori, is a dermal mutant that is characterized as having paired knobs at specific regions of larval segments. In order to clarify the details of cell proliferation which induce knob formation, we tried to detect mitotic cells of larval epidermis by whole mount immunohistochemistry using an antibody specific for M-phase nuclei. The epidermal mitotic activities were compared between the knobbed and the surrounding unknobbed regions during the 4th larval instar. A comparison was also performed in the corresponding epidermal regions between the mutant and normal strains. Mitosis in epidermis of the unknobbed region was mainly observed to occur at 48 h (mid feeding stage) after ecdysis. Conversely, numerous mitotic figures were observed in the knob region at 24 and 48 h after ecdysis. Clear mitotic figures were also observed at the stage just preceding the molting period (72 h). Z-axis observations of propidium iodide stained epidermis using a confocal laser-scanning microscope indicated that the cell nuclei of knob regions were considerably longer and more slender than those of the unknobbed epidermis during the early and middle 4th instar stages. These results suggest that mitosis occurs at the knob regions for most of the intermolt/feeding stage, and that the prolonged cell proliferation observed in the epidermal cells results in an increase of cell number, causing conspicuous outgrowths of integument which takes the form of swollen knobs.
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