An in vivo map of bone morphogenetic protein 2 post‐transcriptional repression in the heart

Abstract

The Bmp2 3'untranslated region (UTR) sequence bears a sequence conserved between mammals and fishes that can post-transcriptionally activate or repress protein synthesis. We developed a map of embryonic cells in the mouse where this potent Bmp2 regulatory sequence functions by using a lacZ reporter transgene with a 3’UTR bearing two loxP sites flanking the ultra-conserved sequence. Cre-recombinase-mediated deletion of the ultra-conserved sequence caused strong ectopic expression in proepicardium, epicardium and epicardium-derived cells (EPDC) and in tissues with known epicardial contributions (coronary vessels and valves). Transient transfections of reporters in the epicardial/mesothelial cell (EMC) line confirmed this repression. Ectopic expression of the recombined transgene also occurred in the aorta, outlet septum, posterior cardiac plexus, cardiac and extra-cardiac nerves and neural ganglia. Bmp2 is dynamically regulated in the developing heart. 3’UTR-mediated mechanisms that restrain BMP2 synthesis may be relevant to congenital heart and vasculature malformations and to adult diseases involving aberrant BMP2 synthesis.

Turning Bone Morphogenetic Protein 2 (BMP2) on and off in Mesenchymal Cells

“…In these cells, which express high levels of Bmp2 , the UCS activates expression by 3 to 5 times the level driven by the Bmp2 promoter alone [Abrams et al, ; Jiang et al, ]. Mesenchymal cell repression is independent of the promoter, coding sequence, and polyadenylation signal [Fukui et al, ; Devaney et al, ; Kruithof et al, ,]. In contrast, we have only observed reporter gene activation in vectors driven by the Bmp2 promoter itself [Abrams et al, ; Jiang et al, ].…”

“…TNF‐α treatment leading to p38 signaling was required to finally produce BMP2 [Fukui et al, ]. Subsequent reporter gene studies in cells and transgenic mice revealed that the UCS may hold BMP2 synthesis at bay in many cell types, including most mesenchymal cells; e.g., primary mouse calvarial cells, C3H10T½ pluripotent mesenchymal cells, vascular smooth muscle cells, perivascular fibroblasts, and heart valve cells [Kruithof et al, ,]. Clinically severe calcification pathologies involving abnormal levels of BMP2 such as calcific aortic valve disease, atherosclerosis, and medial artery calcification occur in mesenchymal tissues [Bostrom et al, ; Yutzey et al, ].…”

Signaling During Epicardium and Coronary Vessel Development

“…30 All these events require highly patterned expression of Bmp2 in the PE/septum transversum region. 31 Bmps thus can be postulated to play a role in establishing the posteriormost myocardial limit (venous pole) of the developing heart. The signals active in this region are detailed in Figure 2.…”

Competing Repressive Factors Control Bone Morphogenetic Protein 2 (BMP2) in Mesenchymal Cells

“…An “ultra‐conserved sequence” (UCS) within the 3′untranslated region (3′UTR) functions as a regulatory switch that facilitates BMP2 down‐regulation in some cells, but promotes up‐regulation in other cells [Abrams et al, ; Fukui et al, ; Devaney et al, ; Jiang et al, ; Kruithof et al, ; Kruithof et al, ]. Reduced levels of UCS‐mediated repression may contribute to pathological BMP2 synthesis.…”