Tài liệu Báo cáo khoa học: Oocyte membrane localization of vitellogenin receptor coincides with

Oocyte membrane localization of vitellogenin receptor

coincides with queen flying age, and receptor silencing

by RNAi disrupts egg formation in fire ant virgin queens

Hsiao-Ling Lu, S. B. Vinson and Patricia V. Pietrantonio

Department of Entomology, Texas A&M University, College Station, TX, USA

Social insects have remarkable forms of social organi￾zation, with the majority exhibiting reproductive divi￾sion of labor between queen and workers [1]. Only a

few females (queens) have the privilege of reproductive

ability and longevity; most females becoming non￾reproductive individuals (workers). Vitellogenesis is a

key process that controls reproduction in insects. It is

under the control of juvenile hormone (JH) and ⁄ or

ecdysone, which are the main inducers of vitellogenin

(Vg) synthesis from the fat body and uptake into

the developing oocyte via vitellogenin receptor (VgR)-

mediated endocytosis [2–6]. Although the ovary-spe￾cific expression and localization of VgR have been

reported from Drosophila, mosquitoes and cockroaches

[7–11], there is a paucity of knowledge on VgR physi￾ology in insects of high reproductive capacity, such as

the queens of social hymenopteran insects (wasps, ants

and bees). Most of the available knowledge on the

molecular mechanisms of reproduction in social insects

is from the honey bee, Apis mellifera; however, bees

have evolved mechanisms which are different from

those in ants and wasps. Contrary to most insects, in

Keywords

insect ovary; insect reproduction; oocyte

development; RNA interference; social

insects

Correspondence

P. V. Pietrantonio, Department of

Entomology, Texas A&M University, College

Station, TX 77843-2475, USA

Fax: +1 979 845 6305

Tel: +1 979 845 9728

E-mail: [email protected]

Website: http://insects.tamu.edu/people/

faculty/pietrantoniop.cfm

(Received 13 March 2009, revised 27 March

2009, accepted 30 March 2009)

doi:10.1111/j.1742-4658.2009.07029.x

In ant species in which mating flights are a strategic life-history trait for

dispersal and reproduction, maturation of virgin queens occurs. However,

the specific molecular mechanisms that mark this transition and the effec￾tors that control premating ovarian growth are unknown. The vitellogenin

receptor (VgR) is responsible for vitellogenin uptake during egg formation

in insects. In the red imported fire ant, Solenopsis invicta Buren (Hymenop￾tera: Formicidae), virgin queens have more abundant VgR transcripts than

newly mated queens, but limited egg formation. To elucidate whether the

transition to egg production involved changes in VgR expression, we inves￾tigated both virgin and mated queens. In both queens, western blot analysis

showed an ovary-specific VgR band ( 202 kDa), and immunofluorescence

analysis of ovaries detected differential VgR localization in early- and late￾stage oocytes. However, the VgR signal was much lower in virgin queens

ready to fly than in mated queens 8 h post mating flight. In virgin queens,

the receptor signal was first observed at the oocyte membrane beginning at

day 12 post emergence, coinciding with the 2 weeks of maturation required

before a mating flight. Thus, the membrane localization of VgR appears to

be a potential marker for queen mating readiness. Silencing of the receptor

in virgin queens through RNA interference abolished egg formation, dem￾onstrating that VgR is involved in fire ant ovary development pre mating.

To our knowledge, this is the first report of RNA interference in any ant

species and the first report of silencing of a hymenopteran VgR.

Abbreviations

dsRNA, double-stranded RNA; EGFP, enhanced green fluorescent protein; JH, juvenile hormone; LDLR, low-density lipoprotein receptor;

RNAi, RNA interference; SiVgR, Solenopsis invicta vitellogenin receptor; Vg, vitellogenin; VgR, vitellogenin receptor.

3110 FEBS Journal 276 (2009) 3110–3123 ª 2009 The Authors Journal compilation ª 2009 FEBS