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First published online December 14, 2006
Journal of Experimental Biology 210, 138-148 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.02652
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Calcium-regulated fusion of yolk granules is important for yolk degradation during early embryogenesis of Rhodnius prolixus Stahl

I. B. Ramos1, K. Miranda2, W. de Souza2, D. M. P. Oliveira1, A. P. C. A. Lima3, M. H. F. Sorgine4 and E. A. Machado1,*

1 Laboratório de Entomologia Médica, Instituto de Biofísica Carlos Chagas Filho (IBCCF), Universidade Federal do Rio de Janeiro (UFRJ), Cidade Universitária - Ilha do Fundão, 21941-590 Rio de Janeiro, RJ, Brasil
2 Laboratorio de Ultraestrutura Celular Hertha Meyer, Instituto de Biofísica Carlos Chagas Filho (IBCCF), Universidade Federal do Rio de Janeiro (UFRJ), Cidade Universitária - Ilha do Fundão, 21941-590 Rio de Janeiro, RJ, Brasil
3 Laboratório de Bioquímica e Biologia Molecular de Proteases, Instituto de Biofísica Carlos Chagas Filho (IBCCF), Universidade Federal do Rio de Janeiro (UFRJ), Cidade Universitária - Ilha do Fundão, 21941-590 Rio de Janeiro, RJ, Brasil
4 Laboratório de Artrópodos Hematófagos, Instituto de Bioquímica Médica (IBQM), Centro de Ciências da Saúde (CCS), Universidade Federal do Rio de Janeiro (UFRJ), Cidade Universitária - Ilha do Fundão, 21941-590 Rio de Janeiro, RJ, Brasil

* Author for correspondence (e-mail: ednildo{at}biof.ufrj.br)

Accepted 8 November 2006

This study examined the process of membrane fusion of yolk granules (YGs) during early embryogenesis of Rhodnius prolixus. We show that eggs collected at days 0 and 3 after oviposition contain different populations of YGs, for example day-3 eggs are enriched in large YGs (LYGs). Day-3 eggs also contain the highest free [Ca2+] during early embryogenesis of this insect. In vitro incubations of day-0 YGs with [Ca2+] similar to those found in day-3 eggs resulted in the formation of LYGs, as observed in vivo. Fractionation of LYGs and small YGs (SYGs) and their subsequent incubation with the fluorescent membrane marker PKH67 showed a calcium-dependent transference of fluorescence from SYGs to LYGs, possibly as the result of membrane fusion. Acid phosphatase and H+-PPase activities were remarkably increased in day-3 LYGs and in calcium-treated day-0 LYGs. Both fractions were found to contain vitellins as major components, and incubation of YGs with calcium induced yolk proteolysis in vitro. Altogether, our results suggest that calcium-induced membrane fusion events take part in yolk degradation, leading to the assembly of the yolk mobilization machinery.

Key words: calcium, embryogenesis, membrane fusion, yolk degradation, yolk granules


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© The Company of Biologists Ltd 2007