An extraovarian protein accumulated in mosquito oocytes is a carboxypeptidase activated in embryos.

Abstract

We report a phenomenon previously unknown for oviparous animals; in Aedes aegypti mosquitoes a serine carboxypeptidase is synthesized extraovarially and then internalized by oocytes. The cDNA encoding mosquito vitellogenic carboxypeptidase (VCP) was cloned and sequenced. The VCP cDNA hybridizes to a 1.5-kilobase mRNA present only in the fat body of vitellogenic females. The deduced amino acid sequence of VCP shares significant homology with members of the serine carboxypeptidase family. Binding assays using a serine protease inhibitor, [3H~diisopropyl fluorophosphate, showed that VCP is activated in eggs at the onset of embryonic development. Activation of VCP is associated with the reduction in its size from 53 kDa (inactive proenzyme) to 48 kDa (active enzyme). The active, 48-kDa, form ofVCP is maximally present at the middle of embryonic development and disappears by the end.

Mosquito Cathepsin B-like Protease Involved in Embryonic Degradation of Vitellin Is Produced as a Latent Extraovarian Precursor

“…Its synthesis in the female fat body is initiated by blood feeding, and the kinetics of its secretion by the vitellogenic fat body are similar to those of the yolk protein precursors, Vg (59) and VCP (42,43).…”

“…Little is known, however, about the process of yolk protein degradation in the mosquito embryo. Previously, we have found that during vitellogenesis, the female fat body, a metabolic tissue analogous to the vertebrate liver, synthesizes and secretes a latent proenzyme of a serine carboxypeptidase which is homologous to yeast carboxypeptidase Y (42,43). This 53-kDa proenzyme, which we named vitellogenic carboxypeptidase (VCP), 1 is specifically accumulated by developing oocytes and deposited in yolk bodies.…”

Calcium-regulated fusion of yolk granules is important for yolk degradation during early embryogenesis of Rhodnius prolixusStahl

“…Activation of these enzymes is achieved by luminal acidification of YGs, a process that is mediated by proton pumps (Fagotto, 1991;Nordin et al, 1991;Mallya et al, 1992;Fagotto, 1995). VT and hydrolases, such as cathepsin B and carboxypeptidase, are known to accumulate in the oocytes during oogenesis and to be stored in YGs (Wall and Meleka, 1985;Oliveira et al, 1986;Raikhel and Dadhialla, 1992;Valle, 1993;Sappington and Raikhel, 1998;Cho et al, 1991;Cho et al, 1999;Liu and Nordin, 1998;Yin et al, 2001). Newly laid eggs are therefore able to initiate VT degradation.…”

“…The exact origin of these hydrolases is poorly understood but some of these enzymes are also taken into the oocytes during oogenesis, being stored near yolk proteins in an inactive state. Aedes aegypti carboxypeptidase (Cho et al, 1991) and cathepsin B-like protease (Cho et al, 1999), Blatella germanica vitellin-processing protease and Xenopus laevis lysosomal enzymes have been shown to accumulate in the oocytes during oogenesis (Wall and Meleka, 1985;Liu and Nordin, 1998;Yin et al, 2001). To activate hydrolases, YGs undergo a process of acidification mediated by proton pumps, such as proton ATPases (H + LYGs.…”

A Novel GATA Factor Transcriptionally Represses Yolk Protein Precursor Genes in the Mosquito Aedes aegypti via Interaction with the CtBP Corepressor

“…In the anautogenous mosquito Aedes aegypti, a key model vector, the fat body produces several YPPs: vitellogenin, vitellogenic carboxypeptidase, and vitellogenic cathepsin B (5,6,8).…”