APOPTOSIS OF LARVAL CELLS DURING AMPHIBIAN METAMORPHOSIS

Programmed cell death occurs in a variety of organs during amphibian m etamorphosis and is usually identified by electron microscopy as apopt osis or its modifications. Because of the massive cell death that occu rs during a short period, amphibian organs serve as an ideal model sys tem for the study of mechanisms underlying programmed cell death. In t his article, a series of morphological changes in apoptosis from their nuclear changes to removal by phagocytic macrophages is reviewed, mai nly in the small intestine of metamorphosing Xenopus Laevis tadpoles. It is well known that cell death during amphibian metamorphosis is und er the control of thyroid hormone (TH), and changes in gene expression induced by TH have been recently analyzed in a few Xenopus organs. On the other hand, there is a growing body of evidence that cell death i s regulated by various kinds of local factors. For example, roles of i nteractions with other tissue cells and/or participation of immunocomp etent cells in cell death have been experimentally shown. Therefore, t o clarify the mechanisms of this complicated process, it is important at present that TH-induced changes in gene expression of each cell typ e comprising the organ are chronologically examined by combining morph ological and molecular biological techniques. (C) 1996 Wiley-Lies, Inc .