Insect Biochemistry and Molecular Biology 30 2000 549–557 www.elsevier.comlocateibmb
Synthesis of vitellogenin by the follicle cells of Rhodnius prolixus
Ana Claudia A. Melo
1,a
, Denise Valle
c
, Ednildo A. Machado
d
, Ana Paula Salerno
a
, Gabriela O. Paiva-Silva
a
, Narcisa L. Cunha E Silva
b
, Wanderley de Souza
b
, Hatisaburo Masuda
a,
a
Departamento de Bioquı´mica Me´dica, Instituto de Cieˆncias Biome´dicas, Universidade Federal do Rio de Janeiro, Rio de Janeiro 21944-590, Brazil
b
Laborato´rio de Ultraestrutura Celular Hertha Meyer, Instituto de Biofı´sica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro 21944-590, Brazil
c
Departamento de Entomologia, Fundac¸a˜o Instituto Oswaldo Cruz, Instituto de Biologia do Exercito, Rio de Janeiro, Brazil
d
Laborato´rio de Entomologia Me´dica, Instituto de Biofı´sica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro 21944-590, Brazil
Received 11 August 1999; received in revised form 24 January 2000; accepted 25 January 2000
Abstract
The synthesis and secretion of vitellogenin by the ovary of Rhodnius prolixus was investigated. Using whole ovary or epithelial cells isolated from follicles of different sizes, it is shown that the follicle cells are a site of synthesis for this protein in the ovary.
The ovaries or follicle cells were incubated in vitro with [
35
S]-methionine or
32
Pi and the secretion of newly synthesized ovarian vitellogenin O-Vg was estimated by the radioactivity associated with the immunoprecipitate or acid-precipitate proteins in the
culture medium. The radioactive O-Vg was analyzed by SDS-PAGE followed by autoradiography or after elution from a DEAE- Toyopearl column. The presence of O-Vg inside the follicle cells was detected by immunofluorescence and immunogold labels.
Both methods revealed strong labeling inside the follicle cells. While the capacity for total protein synthesis by the follicle cells was maximal during the early phase of vitellogenesis in small follicles, the synthesis of O-Vg reached its peak during the late
phase of oocyte growth, just before formation of the chorion. A possible role for ovarian vitellogenin in Rhodnius and its relationship with Vg synthesis by the fat body is discussed.
2000 Elsevier Science Ltd. All rights reserved.
Keywords: Ovary; Synthesis of vitellogenin; Follicle cells; Rhodnius
1. Introduction
Since embryonic development of insects occurs in iso- lation from the maternal body, the egg can survive only
if it contains all necessary material for the embryo’s
Abbreviations: O-Vg =
ovarian vitellogenin; VT =
vitellin; Vg =
vitellog- enin; DEAE
= diethylaminoethyl; LBTI
= lima bean trypsin inhibitor;
32
Pi =
[
32
P]-Pi radioactive inorganic phosphate; SBTi =
soybean trypsin inhibitor; SDS
= sodium dodecyl sulphate; SDS-PAGE
= Polyacrylamide
gel electrophoresis in the presence of SDS; DME =
Dulbecco’s modified Eagles’s medium; NP40
= octylphenol-polyethoxyethanol; NBT
= Ni-
troblue tetrazolium;
BCIP =
bromo-chloro-indoyl phosphate;
PBS =
phosphate-buffered saline. Corresponding author. Fax:
+ 55-21-270-8647.
E-mail address: masudabioqmed.ufrj.br H. Masuda.
1
Present address: Departamento de Patologia, Centro de Cieˆncias Patolo´gicas, Universidade Federal do Para´.
0965-174800 - see front matter
2000 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 5 - 1 7 4 8 0 0 0 0 0 2 3 - 0
growth. This material, the yolk, composed of proteins, sugars and lipids, is stored in an organized manner inside
the egg. In most insects, a single phospholipoglycoprot- ein, vitellin Vt, is the main component of eggs and
serves both for embryonic and in some cases, early larval development Postlethwait and Giorgi, 1985; Zhu et al.,
1986; Oliveira et al. 1986, 1989. Vitellin is derived from vitellogenin Vg, which in most insects is synthe-
sized exclusively by fat bodies Valle et al., 1993. Oocytes are specialized for accumulating this Vt precur-
sors by receptor-mediated endocytosis as reviewed by Telfer et al., 1982; Raikhel and Dhadialla, 1992.
The single layer of follicle cells that surrounds oocytes constitutes an additional barrier to yolk precursors
entering the oocyte. Interfollicular channels have been described in Hyalophora cecropia Telfer, 1961, Rhod-
nius prolixus
Davey, 1981,
Locusta migratoria
550 A.C.A. Melo et al. Insect Biochemistry and Molecular Biology 30 2000 549–557
Lauverjat et al., 1984 and mosquitoes Raikhel and Lea, 1991. These channels, which are transient, undergo
dramatic changes in patency in Rhodnius during oocyte maturation and this change correlates perfectly with the
rate of vitellogenin uptake Oliveira et al., 1986.
In addition to accumulating Vg synthesized by the fat body the ovaries also synthesize proteins that are
required for embryonic development. The commitment of follicle cells to this process is well known Melius
and Telfer, 1969; Anderson and Telfer 1969, 1970. In some organisms the ovary has been described as the site
of synthesis of non-vitellin yolk proteins such as paravit- ellogenin in Hyalophora cecropia Telfer et al., 1981
and egg-specific protein in Bombyx mori Irie and Yama- shita, 1983. Synthesis of vitellogenin by ovaries so far
has been demonstrated only in higher Diptera and some Coleoptera Postlethwait et al., 1980; Bownes, 1982;
Brennan et al., 1982; Fourney et al., 1982; Zhai et al., 1984; Bianchi et al., 1985; Peferoen and De Loof, 1986;
Zongza and Dimitriadis, 1988. To our knowledge there are no reports bearing on the possibility of Vg synthesis
by ovarian tissues of Hemiptera.
In this work, the ovaries of the hemipteran Rhodnius prolixus are shown to synthesize Vg. Follicle cells sur-
rounding large oocytes are active in this process, and it is shown that follicle cells continue to produce Vt even
after closure of interfollicular channels, i.e. that are no longer engaged in the uptake of yolk precursors from
the hemolymph. A possible role of R. prolixus ovarian Vg is considered.
2. Materials and methods
