Ref ID : 7589
Guy Morat, Maria Giovanna Chessa, and Tina Crippa-Franceschi; [Etude de la Regulation des Teneurs en ADN Nucleaire au Cours de la Reproduction Vegetative et de L'enkystement D'attente chez le Cilie Colpoda cucullus]. Protistologica XVII(3):313-329, 1981
Reprint
In File
Notes
Four stages of the complete cell cycle of Colpoda cucullus have been studied: - cells just before the reproductive cyst formation, - young daughter cells yielded from reproductive cysts, - active interphasic cells, - young durable resting cysts. The ADN contents in micronuclei and macronuclei, in extrusion bodies of resting cysts, hae been determined by a cytophotometric technique following a Feulgen staining. Our results show that, during the cell growth, the macronucleus gets a DNA quantity depending, not only on the conditions of the environment (mainly on food abundance), but also on the DNA content received at the previous reproductive cycle. 1) On favourable growth conditions, usually two successive cell divisions take place within the reproductive cyst. In that case, a two-fold macronuclear DNA replication happens during the Ciliate active life; the nuclear division only lets a distribution, often unequal, in the four resulting cells. The early and fast micronuclear DNA duplication precedes the macronuclear synthesis and we have to guess a second micronuclear cycle occurring between the two divisions inside the cyst. The regulatory process charged with keeping inside a certain range the G1 and G2 macronuclear levels looks quite tangled. Two hypotheses may be tested: - Starting from a low G1 value to make up for the combined effect of the chromatin extrusion and of the unequal DNA distribution thus avoiding the overdecrease of G1 content, Colpoda cucullus would carry out a third synthesis phase which restores a high G1 content at the following generation; on the contrary starting from a high G1 content only one synthesis phase will take place before the cyst division. - Starting from a G1 content either low, medium or high, Colpoda cucullus will carry out a continuous oversynthesis broken by the division as observed in Tillina magna. 2) Under depletion conditions, the depolyploidization of the macronucleus precedes the encystment. This encystment goes along with a macronuclear extrusion; its content is related with the amount of the "precystic" cell. Hence it results a clear nucleo-cytoplasmic relation in the young resting cysts. Extrusion bodies include a variable number of "macronuclear sub-units" which should not always hold the diploid micronuclear quantity. This fact may be explained with a selective genic amplification in the (or some) sub-units.