The cell biology of mosquito vitellogenesis

Abstract

Insect vitellogenesis involves coordinated activities of the fat body and oocytes. We have studied these activities at the cellular level in the mosquito. During each vitellogenic cycle, the fat body undergoes three successive stages: 1) proliferation of biosynthetic organelles, 2) vitellogenin synthesis, 3) termination of vitellogenin synthesis and degradation of biosynthetic organelles by lysosomes. Analysis with monoclonal antibodies and radiolabelling demonstrated that the mosquito yolk protein consists of two subunits (200-kDa and 65-kDa). Both subunits are glycosylated, their carbohydrate moieties are composed of high-mannose oligosaccharides. The yolk protein subunits are derived from a single 220 kDa precursor detected by an in vitro translation. Oocytes become competent to internalize proteins as a result of juvenile hormone-mediated biogenesis of endocytotic organelles. The yolk protein is then accumulated by receptor-mediated endocytosis. A pathway of the yold protein and factors determining its routing in the oocyte have been studied.

A transcriptome analysis of the Aedes aegypti vitellogenic fat body

“…aegypti have been described ( Hamblin et al 1987 ) while the multiple transcripts with similarity to cathepsin B and vitellogenic carboxypeptidase indicate that these proteins may be encoded by more than one gene as well. It has been already established that vitellogenin, vitellogenic carboxypeptidase and cathepsin B are synthesized by the fat bodies in response to a blood meal, secreted into the hemolymph and accumulate in ovaries, where they are deposited in the oocytes during development ( Raikhel, 1987 ; Raikhel, et al, 2002 ; Raikhel and Lea, 1983 ; Ribeiro, 2003 ).…”

Vitellogenin gene expression in autogenous Culex tarsalis

“…Expression of multiple vitellogenin genes during reproduction is consistent with the hypothesis of a functional conservation of duplicated genes for increased dosage (Ohno, 1970; Clemments, 2000; Sugino & Innan, 2006; Tufail & Takeda, 2008). During previtellogenic development the fat body cells of the mosquito become polyploid, increasing the copy number of genes that will contribute to vitellogenin synthesis (Raikhel & Lea, 1983; Raikhel, 1987; Clemments, 2000). Multiple active copies of vitellogenin genes, subsequently multiplied by fat body cell ploidy, are likely to contribute to the rapid and abundant production of transcript for yolk protein.…”

Vitelogênese do mosquito Culex quinquefasciatus

“…Este processo foi mais detalhadamente estudado em Ae. aegypti (Behan e Hagedorn, 1978;Raikhel e Lea, 1983;Raikhel, 1984;Raikhel et al, 1986;Raikhel, 1987b;Snigirevskaya et al, 1997a, b;Briegel et al, 2003), sendo este modelo utilizado como padrão para todos os mosquitos. Antes da alimentação com sangue, as fêmeas encontram-se na fase pré-vitelogênica, na qual as células do corpo gorduroso e dos folículos ovarianos estão sendo preparadas para a produção, absorção e processamento da vitelogenina (Vg; Raikhel e Lea, 1983).…”