Cell death in development: shaping the embryo

Abstract

Cell death in animals is normally classified as type I (apoptotic), type II (autophagic) or necrotic. Of the biologically controlled types of death, in most embryos apoptosis is the most common, although in metamorphosis and in cells with massive cytoplasm type II is often seen, and intermediate forms are seen. For vertebrate embryos other than mammals, apoptosis is not seen prior to gastrulation but thereafter is used to sculpt the organs of the embryo, while overproduction of cells with subsequent death of excess cells is a common means of generating high specificity with low information cost. In zebrafish at least, the inability of embryos prior to the maternal-zygotic transition to undergo apoptosis appears to derive from the inability of the cells to resist lysis once apoptosis begins, rather than any inhibition of apoptosis. In mammalian embryos, apoptosis is seen during cavitation. Thereafter, as in other embryos, cell death plays a major role in shaping and sculpting the embryo. In those situations that have been carefully studied, cell death is under tight genetic control (including regulation of gene products whose function in cell death is not yet known, such as cdk5), with activation of apoptosis sometimes regulated by local environmental variables.

Requirement for deoxycytidine kinase in T and B lymphocyte development

“…By recycling these deoxyribonucleosides via the fast salvage pathway and reconverting them into dNTPs at a low ATP cost, rapidly dividing lymphocyte precursors may decrease their dependency on the slower and significantly more ATP demanding (4-fold) de novo synthesis. The analysis of the dCK KO mice shows that a similar requirement for active deoxyribonucleoside salvage does not seem to apply during embryogenesis, organogenesis, and tissue remodeling, processes that also involve high rates of proliferation and death (28). It remains to be determined whether dCK is required for the formation of germline cells.…”

Atg7-dependent autophagy promotes neuronal health, stress tolerance, and longevity but is dispensable for metamorphosis in Drosophila

“…Indeed, recent reports showed that basal autophagy plays an essential role in protein quality control in mammals, by continuously degrading misfolded or damaged proteins (Komatsu et al 2005(Komatsu et al , 2006Hara et al 2006), and prevents metabolic stress-induced genome instability and tumor progression (Mathew et al 2007). During development, high levels of autophagy may also contribute to some forms of programmed cell death, as in the case of degenerating larval tissues during insect metamorphosis (Butterworth and Forrest 1984;Neufeld 2004;Penaloza et al 2006).…”

Le dernier sursaut des cellules mourantes

“…Ainsi, l'apoptose apparaît comme un processus cellulaire qui doit être finement régulé. Outre son rôle dans différents contextes pathologiques, l'apoptose est essentielle au cours du développement [2,3]. C'est d'ailleurs dans ce contexte qu'elle a été initialement identifiée chez des organismes modèles tels que le ver à soie et le têtard.…”

“…Ces corps apoptotiques permettent une élimina-tion « propre » des cellules, sans déver-sement du contenu cellulaire à l'exté-rieur, et donc sans inflammation ; ils seront ensuite éliminés par les macrophages. Au cours du développement, l'apoptose permet de réguler le nombre de cellules au sein d'un tissu, mais aussi de sculpter différentes structures [2,3]. Parmi les diffé-rents modèles de morphogenèse dépendant de l'apoptose (coeur, intestin, mains), la formation des doigts chez les vertébrés a été très étudiée.…”