Control of Transcriptional Repression of the Vitellogenin Receptor Gene in Largemouth Bass (Micropterus Salmoides) by Select Estrogen Receptors Isotypes

Abstract

The vitellogenin receptor (Vtgr) plays an important role in fish reproduction. This receptor functions to incorporate vitellogenin (Vtg), a macromolecule synthesized and released from the liver in the bloodstream, into oocytes where it is processed into yolk. Although studies have focused on the functional role of Vtgr in fish, the mechanistic control of this gene is still unexplored. Here we report the identification and analysis of the first piscine 5' regulatory region of the vtgr gene which was cloned from largemouth bass (Micropterus salmoides). Using this putative promoter sequence, we investigated a role for hormones, including insulin and 17β-estradiol (E2), in transcriptional regulation through cell-based reporter assays. No effect of insulin was observed, however, E2 was able to repress transcriptional activity of the vtgr promoter through select estrogen receptor subtypes, Esr1 and Esr2a but not Esr2b. Electrophoretic mobility shift assay demonstrated that Esr1 likely interacts with the vtgr promoter region through half ERE and/or SP1 sites, in part. Finally we also show that ethinylestradiol (EE2), but not bisphenol-A (BPA), represses promoter activity similarly to E2. These results reveal for the first time that the Esr1 isoform may play an inhibitory role in the expression of LMB vtgr mRNA under the influence of E2, and potent estrogens such as EE2. In addition, this new evidence suggests that vtgr may be a target of select endocrine disrupting compounds through environmental exposures.

Maternal investment in fish oocytes and eggs: The molecular cargo and its contributions to fertility and early development

“…Regarding the endocrine regulation of expression of genes encoding ovarian lipoprotein receptors in fish, only two reports on the vtgr of largemouth bass, Micropterus salmoides, are available (Dominguez et al, 2012(Dominguez et al, , 2014. The vtgr transcript in this species showed the same pattern of expression during oogenesis as described above for cutthroat trout and striped bass, being maximally expressed in primary growth oocytes with expression decreasing during vitellogenesis.…”

“…The co-exposures with insulin and steroid hormones also increased estrogen receptor (esr2b) and androgen receptor (ar) transcript levels, suggesting a role for these receptors in regulating the insulin-mediated signaling pathways (Dominguez et al, 2012). In a subsequent study, the 5' regulatory region of the vtgr gene in this species was cloned and the promoter sequence was used to investigate endocrine regulation of vtgr expression in cell-based promoter activation (reporter) assays (Dominguez et al, 2014). E2 was able to repress transcriptional activity of the vtgr promoter through select estrogen receptor subtypes (Esr1 and Esr2a but not Esr2b) and evidence was obtained indicating that Esr1 likely interacts with the vtgr promoter through non-consensus ERE or SP1 DNA binding sites.…”

The POU Transcription Factor POU-M2 Regulates Vitellogenin Receptor Gene Expression in the Silkworm, Bombyx mori

“…Notably, we found multiple POU CREs in the VgR promoters of six insect species representing three diverse taxonomic groups. It was also reported that POU CREs exist on the upstream regulatory region of the VgR gene in M. salmoides [7]. These clues suggested a possible regulatory role of POU factors in VgR transcription.…”

“…VgR regulation by POU domain transcription factors may be a common phenomenon in insects, as well as in other oviparous species. In the past three decades, POU domain transcription factors were identified in insects and many other oviparous species, such as the fishes M. salmoides and Paralichthys olivaceus, the amphibian Xenopus laevis, and the nematode C. elegans [7,[49][50][51][52]. Notably, we found multiple POU CREs in the VgR promoters of six insect species representing three diverse taxonomic groups.…”

Resolving the complexity of vitellogenins and their receptors in the tetraploid Atlantic salmon (Salmo salar): Ancient origin of the phosvitin‐less VtgC in chondrichthyean fishes

“…Contrasting with the increased hepatic expression of salmon vtgAsa1 during maturation, the ovarian expression of the vtgr paralogs peaked at the previtellogenic stage and gradually decreased, concomitant with the increased plasma E 2 levels and ovarian growth. Accordingly, activated estrogen receptors were shown to stimulate vtg transcription and to stabilize vtg transcripts (Bouter et al, 2010;Brock & Shapiro, 1983;Flouriot, Pakdel, & Valotaire, 1996), but could also repress vtgr transcriptional activity, as reported in largemouth bass (Micropterus samonides) (Dominguez, Bisesi, Kroll, Denslow, & Sabo-Attwood, 2014). The decreased ovarian expression of the salmon vtgrs during vitellogenesis seems to contradict the 100-fold increase in receptor abundance per oocyte in rainbow trout (Lancaster & Tyler, 1994;Rodriguez, Bon, & Le Menn, 1996).…”