LABORATORY OF MORPHODIVERSITY

Associate Professor: KODAMA, Ryuji

The aim of this laboratory is to observe the variety of the morphogenetic processes in the course of the ontogenesis of multicellular ogranisms and to analyze the mechanisms of such processes mainly by morphological methods. Accumulation of such analyses on embryogenetic processes of related species is expected to give an insight in the evolution of morphogenetic processes. This laboratory uses the wings of lepidopteran species for the material of morphological studies.

Wings of the lepidopteran insects (butterflies and moths) develop from the wing imaginal disc, which is a hollow sac made of simple epithelium.Due to its simple construction, this tissue is a good material to study cellular interactions in the course of morphogenesis.

The outline shape of the adult wing is often different from that of the pupal wing.This difference is brought about by the programmed cell death of the marginal area of the pupal wing.The marginal dying area is called "the degeneration region" and the internal area, which develop into the adult wing, is called "the differentiation region".

The cell deaths in the degeneration region proceeds very rapidly and completes in a half to one day period in Pieris rapae or several other species examined.It was shown that the dying cells in the degeneration re­gion have characteristics common with the apop­totic cell death in mammalian cells, such as fragmented and condensed nuclei containing short DNA fragments detected by TUNEL staining. The cells in the degeneration region are actively en­gulfed by the macrophages in the cavity beneath the wing epithelium.The macrophages seem to be concentrated beneath the degeneration region by the strong adhesion between basal surfaces of the dorsal and ventral epithelium in the differentiation region, which occurs at the time of prominent cell death and excludes macrophages out of the differentiation region. Thus realised concentration of macrophages seems to accelerate the shrinkage of the degeneration region.

A collaborative work with the laboratory of Dr. K. Watanabe (Hiroshima University) concerns mostly on the development of trachea and tracheole pattern in the swallow tail butterflies.Trachea and tracheoles are both important in delivering air into the wing and their pattern coincide with that of the boundary of degeneration and differentiation zones at the distal end of the wing. According to the observations, the pattern formation of wing epithelium is often dependent on tracheal and tracheole patterns.Basic research on the development of tracheal pattern formation is being done by the scanning electron microscopy and the bright field light microscopy of the fixed or fresh specimens to describe the exact pathway and the time course of the formation of elaborate pattern of trachea and tracheoles and to establish the cytological and developmental relationship between the formation of tracheal pattern and epithelial cell pattern, such as scale cell pattern.

This laboratory also conduct morphological observation of several animal tissues by scanning and transmission electron microscopy and immno-electron microscopic analyses. The training of specimen preparation and instrument operation for such observations is also given. These activities include the Division of Sex Differentiation and the Laboratory of Neurophysiology of our institute.