Direct Response Elements of BMP within the PV.1A Promoter Are Essential for Its Transcriptional Regulation during Early Xenopus Development

Abstract

Xvent homeobox genes encode transcription factors that repress organizer genes and are essential for dorsoventral specification during early embryogenesis in Xenopus. In contrast to the Xvent-2 gene subfamily, Xvent-1 subfamily members, including PV.1A, have been proposed as indirect targets of Bone Morphogenetic Protein-4 (BMP-4) signaling. Because PV.1A is a critical downstream mediator of, and tightly regulated by, BMP-4 signaling, we hypothesized that its promoter contains a direct BMP-4 response element to effect this transcriptional regulation. We demonstrate that direct regulation by BMP-4 is necessary for transcription of PV.1A: its proximal promoter contains cis-acting binding elements for Smads and Oaz crucial to induction in response to BMP-4 signaling. In addition to these direct cis-acting BMP-4 responsive elements, an indirect Xvent-2 response element and several repressive elements exist in the PV.1A promoter to regulate its transcription. In summary, PV.1A undergoes combinatorial regulation during early Xenopus development as both the direct target of BMP-4 signaling and as the direct and indirect target of positive and negative regulatory factors.

Xbra and Smad-1 response elements cooperate in PV.1 promoter to inhibit the early neurogenesis inXenopusembryos

“…5’-flanking region of PV.1 contains various cis-acting response elements, including Xvent-2, Oaz and Smads and triggers the PV.1 transcriptional activation for regulating BMP-4 signaling (Lee et al, 2011). Our above findings suggested that PV.1 promoter region may contain putative cis-acting XbRE.…”

“…Our previous study documented that BMP-4/Smad-1 directly binds to the endogenous promoter of PV.1 and induces PV.1 expression during Xenopus development (Lee et al, 2011). Our recent study showed that FGF/Xbra induces PV.1 expression and negatively regulates the early neurogenesis (Yoon et al, 2014b).…”

“…Previously, a study demonstrated that Smad-1 is a co-transcriptional activator of BMP signaling and directly binds with cis-acting BMP-4 response elements (BRE; CAGACT, −180bp to −162bp) within upstream region of putative transcriptional initiation site of PV.1 (Lee et al, 2011). Moreover, another study has been documented that phosphorylated C-terminal domain of Smad-1 physically interacts with the N-terminal domain of Xbra.…”

“…Our previous study documented that PV.1 promoter region contains the cis-acting BRE (CAGACT, −180bp to −162bp) within 5’-flanking region of putative transcription initiation site of PV.1 (Lee et al, 2011). Moreover, PV.1 is a direct target of BMP signaling and positively regulates the transcriptional activation of PV.1 to inhibit the early neurogenesis (Lee et al, 2011).…”

“…Our previous study documented that PV.1 promoter region contains the cis-acting BRE (CAGACT, −180bp to −162bp) within 5’-flanking region of putative transcription initiation site of PV.1 (Lee et al, 2011). Moreover, PV.1 is a direct target of BMP signaling and positively regulates the transcriptional activation of PV.1 to inhibit the early neurogenesis (Lee et al, 2011). Another study documented that C-terminal mutated Smad-1 at S378N, Y336D and Y343D abolishes the interaction of Smad-1 with Xbra and C-terminal phosphorylated Smad-1 plays a significant role in Smad-1-Xbra interaction (Messenger et al, 2005).…”