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

Abstract

Vitellogenin receptors (VgRs) play critical roles in egg formation by transporting vitellogenin (Vg) into oocytes in insects. Although the function of VgR in insects is well studied, the transcriptional regulation of this gene is still unclear. Here, we cloned the promoter of the VgR gene from Bombyx mori (BmVgR), and predicted many POU cis-response elements (CREs) in its promoter. Electrophoretic mobility shift and chromatin immunoprecipitation assays showed that the POU transcription factor POU-M2 bound directly to the CREs of the promoter. Overexpression of POU-M2 in an ovarian cell line (BmNs) enhanced BmVgR transcription and promoter activity detected by quantitative reverse transcription PCR and luciferase reporter assays. Analyses of expression patterns indicated that POU-M2 was expressed in ovary at day two of wandering stage initially, followed by BmVgR. RNA interference of POU-M2 significantly reduced the transcription of BmVgR in ovary and egg-laying rate. Our results suggest a novel function for the POU factor in silkworm oogenesis by its involvement in BmVgR regulation and expands the understanding of POU factors in insect VgR expression.

Homeodomain proteins POU‐M2, antennapedia and abdominal‐B are involved in regulation of the segment‐specific expression of the clip‐domain serine protease gene CLIP13 in the silkworm, Bombyx mori

“…In this study, we found that expression of homeodomain transcription factors POU-M2, Antp, and Abd-B was upregulated by 20E, and further demonstrated that these transcription factors were involved in the transcriptional regulation of CLIP13 by directly binding to CREs in its promoter region. Previous studies indicated that insect homeodomain transcription factors played pivotal roles in segment determination, tissue development, cell fate determination of imaginal discs, egg formation, and ecdysteroidogenesis (Lewis, 1978;Bondos et al, 2004;Meng et al, 2015;Shen et al, 2020). Our findings provide new insight into the functions of homeodomain transcription factors in insect molting.…”

“…During insect metamorphosis, POU-M2 reportedly interacted with abdominal-A (abd-A) to regulate expression of WCP4 and other WCPs to complete postembryonic development and differentiation of the wing discs (Deng et al, 2011(Deng et al, , 2012. In addition, POU-M2 was shown to play an important role in insect vitellogenesis by directly regulating expression of Vg and VgR (Lin et al, 2017;Shen et al, 2020). In the present study, we found that POU-M2 was involved in transcriptional regulation of CLIP13 in the epidermis.…”

“…S5). Multiple POU-M2 binding sites in the target gene promoter may be a molecular mechanism that precisely regulates expression level of the target gene (Meng et al, 2015;Shen et al, 2020).…”

“…POU-M1 was reportedly expressed in multiple tissues and participated in transcriptional regulation of sericin genes in the silk gland (Matsunami et al, 1998;Takiya et al, 2011). POU-M2, which differs from POU-M1 in amino acid residues 108-136, was involved in transcriptional regulation of many important genes, including diapause hormone, pheromone biosynthesis-activating neuropeptide, wing disc cuticle protein (WCP), vitellogenin (Vg), and vitellogenin receptor (VgR) (Zhang et al, 2004;Deng et al, 2012;Lin et al, 2017;Shen et al, 2020). POU-M2 was also found to be a regulator of the 20E synthesis pathway by binding to the cis-response elements (CREs) of the steroidogenic enzyme gene Phantom (Phm) via interaction with Antp in B. mori (Meng et al, 2015).…”

POU-M2 promotes juvenile hormone biosynthesis by directly activating the transcription of juvenile hormone synthetic enzyme genes in Bombyx mori

“…In Drosophila melanogaster , the POU factor drifter regulates cell proliferation and differentiation of wing imaginal discs [21], the differentiation and migration of tracheal cells and neurons [22,23], and the expression of dopa decarboxylase [24]. In Bombyx mori , the POU factor POU-M1 is involved in the transcription of sericin-1 gene [25], and POU-M2 regulates the expression of fibroin heavy chain (fib-H) [26,27], wing disc cuticle protein 4 (WCP4) [28,29], steroidogenic enzyme phantom [30], vitellogenin (Vg) [31], vitellogenin receptor (VgR) [32], and diapause hormone and pheromone biosynthesis-activating neuropeptide (DH-PBAN) [33]. Also, POU-M2 regulates the expression of DH-PBAN and phosphatase and tensin homologue in Helicoverpa armigera [34,35].…”