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- Biochemical and molecular aspects of insect vitellogenins
- Vg genes and their regulation in insects
- Vg gene as a target of endocrine disruptors
- Molecular mechanism of Vg gene transcription
- Hormonal regulation of Vg gene transcription in different insect groups
Vitellogenins (Vg) genes code for the major egg yolk protein precursor in insects and many other oviparous species. In insects, the Vg gene is expressed extra-ovarially in the fat body in sex-, tissue- and stage-specific manners. During the reproductive phase, the Vg mRNA is expressed in large quantities, which is then translated, secreted into hemolymph and ultimately taken up by the developing oocytes through receptor-mediated endocytosis. Once sequestered, the Vgs are stored as vitellin (Vn), the main nutritional reserve for the developing embryo. The regulation of Vg genes is directly under the control of hormones at the transcriptional level. Hormones involved in Vg gene transcription are juvenile hormone (JH), ecdysteroids and some neuropeptides. The overall understanding that has emerged is that the insects can be classified, based on the system of hormonal regulation of Vg gene transcription, into three groups: (i) insects (like most of hemipterans) that use only JH for Vg gene transcription; (ii) insects (like dipterans) that need both JH and ecdysteroids for Vg regulation; and (iii) insects like lepidopterans that require JH, ecdysteroids and additional hormones to regulate their reproductive biology. However, why insect species diverge in using different hormones to govern their reproductive physiology remains unclear. The present contribution focuses on the current status of knowledge regarding the regulation of Vg genes in insects. Besides a brief information on biochemical and molecular features, the role of Vg genes as a target of endocrine disruptors will be addressed. Also, the molecular mechanism of Vg gene regulation will be discussed.