Identification and Transcriptional Modulation of the Largemouth Bass, Micropterus salmoides, Vitellogenin Receptor During Oocyte Development by Insulin and Sex Steroids1

Abstract

Fish vitellogenin synthesized and released from the liver of oviparous animals is taken up into oocytes by the vitellogenin receptor. This is an essential process in providing nutrient yolk to developing embryos to ensure successful reproduction. Here we disclose the full length vtgr cDNA sequence for largemouth bass (LMB) that reveals greater than 90% sequence homology with other fish vtgr sequences. We classify LMB Vtgr as a member of the low density lipoprotein receptor superfamily based on conserved domains and categorize as the short variant that is devoid of the O-glycan segment. Phylogenetic analysis places LMB Vtgr sequence into a well-supported monophyletic group of fish Vtgr. Real-time PCR showed that the greatest levels of LMB vtgr mRNA expression occurred in previtellogenic ovarian tissues. In addition, we reveal the effects of insulin, 17beta-estradiol (E 2 ), and 11-ketotestosterone (11-KT) in modulation of vtgr, esr, and ar mRNAs in previtellogenic oocytes. Insulin increased vtgr expression levels in follicles ex vivo while exposure to E 2 or 11-KT did not result in modulation of expression. However, both steroids were able to repress insulin-induced vtgr transcript levels. Coexposure with insulin and E 2 or of insulin and 11-KT increased ovarian esr2b and ar mRNA levels, respectively, which suggest a role for these nuclear receptors in insulin-mediated signaling pathways. These data provide the first evidence for the ordered stage-specific expression of LMB vtgr during the normal reproductive process and the hormonal influence of insulin and sex steroids on controlling vtgr transcript levels in ovarian tissues.insulin, oocyte development, steroid hormones, vitellogenin, vitellogenin receptor

Triacylglyceride physiology in the short-finned eel,Anguilla australis—changes throughout early oogenesis

“…Relative transcript copy number of apoe in the ovary increased as did that of lpl, quite possibly as a mechanism to supply more lipoprotein-harnessed energy (i.e., lipids) to the tissue. Relative transcript copy number of the vtgr also increased, corresponding well with the assumed onset of vitellogenin uptake and expression patterns seen in other species of fish (11,20,27,50,56,58). Relative transcript copy number of the ldlr increased from the perinucleolar stage to the oil droplet stage.…”

The observed oogenesis impairment in greater amberjack Seriola dumerili (Risso, 1810) reared in captivity is not related to an insufficient liver transcription or oocyte uptake of vitellogenin

“…In teleost fish, as in other oviparous animals, Vtg is specifically incorporated in the developing oocytes through a process of endocytosis, mediated by vitellogenin receptors (VtgRs) that are orthologous to the mammalian very low density lipoprotein receptor (VLDLR; Hiramatsu, Chapman, Lindzey, Haynes & Sullivan, ). The mechanisms that regulate VtgR and other VLDLR expression in fish have not yet been clarified (Chakraborty et al., ; Dominguez et al., ; Pousis et al., ). However, a role of the diet, particularly of lipid intake, in the regulation of VtgR expression and Vtg oocyte uptake is expected, based on evidence on Senegalese sole Solea senegalensis (Kaup, 1858) in which liver VLDLR overexpression was associated to a high fat diet (Borges et al., ).…”

Gene Expression Networks Underlying Ovarian Development in Wild Largemouth Bass (Micropterus salmoides)

“…The authors go on to suggest that transcript levels may be used as a precocious functional molecular marker of the number of oocytes recruited for vitellogenesis. In a recently published study, LMB vitellogenin receptor ( vtgr ) mRNA was most highly expressed during PN and CA, just before the VTGR protein is required on the plasma membrane for VTG endocytosis into oocytes [38]. In addition, there was an increase in apolipoprotein expression throughout LMB oocyte development, including preproapolipoprotein A-I , apolipoprotein A-IV4 (apoA-IV4 ) and apoe, but the expression was higher for some (7 to 8-fold) during the secondary growth phase.…”