Generation of a new mouse line with conditionally activated signaling through the BMP receptor, ACVR1: A tool to characterize pleiotropic roles of BMP functions

Abstract

BMP signaling plays pleiotropic roles in various tissues during embryogenesis and after birth. We have previously generated a constitutively activated Acvr1(ca-Acvr1) transgenic mouse line (line L35) through pronuclei injection to investigate impacts of enhanced BMP signaling in a tissue specific manner. However, line L35 shows a restricted expression pattern of the transgene. Here, we generated another ca-Acvr1 transgenic line, line A11, using embryonic stem (ES) transgenesis. The generated line A11 shows distinctive phenotypes from line L35, along with very limited expression levels of the transgene. When the transgene is activated in the neural crest cells in a Cre-dependent manner, line A11 exhibits cleft palate and shorter jaws, while line L35 develops ectopic cartilages and highly hypomorphic facial structures. When activated in limb buds, line A11 develops organized but smaller limb skeletal structures, while line L35 forms disorganized limbs with little mineralization. Additionally, no heterotopic ossification (HO) is identified in line A11 when bred with NFATc1-Cre mice even after induction of tissue injury, which is an established protocol for HO for line L35.Therefore, the newly generated conditional ca-Acvr1 mouse line A11 provides an additional resource to dissect highly context dependent functions of BMP signaling in development and disease.

BMP signaling during craniofacial development: new insights into pathological mechanisms leading to craniofacial anomalies

“…There are still questions why three transgenic mice, i.e., caBmpr1a mice, caAcvr1-L35 mice, and caAcvr1-A11 mice crossed with P0-Cre mice, showed different phenotypes. We found that the phosphorylation level of SMAD1/5/9 differs between caAcvr1-L35 mice and caAcvr1-A11 mice ( Yang et al, 2021b ), which may be a reason for similar but distinct phenotypes between these two lines. Another possibility is that because these mice have been generated through random transgenesis, their expression patterns may be different depending on the genomic locus where the transgenic constructs are integrated.…”

“…Although the phenotype differences between us and other laboratories might be developed by the difference of Wnt1-Cre mice and P0-Cre mice, it is reasonable to speculate that unbalance between the SMAD-dependent and SMAD-independent pathways in cranial NCCs may be a reason for an orofacial cleft in P0-Cre;caBmpr1a fl/+ ;Tak1 fl/fl mice. We recently reported that two transgenic mouse lines expressing constitutively activated Acvr1 ( caAcvr1 , Acvr1 with the Q207D mutation) in NCCs in mice ( P0-Cre;caAcvr1-L35 line and P0-Cre;caAcvr1-A11 line ) develops midfacial defects including orofacial cleft ( Yang et al, 2021a ; Yang et al, 2021b ). Interestingly, the facial phenotypes between P0-Cre;caAcvr1-L35 line and P0-Cre;caAcvr1-A11 line are different.…”

A BMP-controlled metabolic/epigenetic signaling cascade directs midfacial morphogenesis

“…While the expression of constitutively activated Bmpr1a in CNCCs did not affect overt midfacial structures (24)(25)(26), we sought to define the in vivo impact of increased BMP/Smad signaling via ACVR1, another type I BMP receptor, on midfacial morphogenesis. To this end, we generated a transgenic mouse model with a floxed constitutively activated Acvr1 allele (line A11, ca-Acvr1(A11)) (27) and crossed it with P0-Cre (28) to enhance BMP/Smad signaling in a neural crest-specific manner. Unexpectedly, we found that over 85% of the ca-Acvr1(A11) mutants (ca-Acvr1(A11) fl/+ ;P0-Cre) displayed drastic midline facial defects, including a midline facial cleft, missing primary palate, bifurcated nasal septum, and short snout (Figure 1, B and C, and Supplemental Figure 1, A-C; supplemental material available online with this article; https://doi.org/10.1172/JCI165787DS1).…”

“…In addition to craniofacial morphogenesis, defects were identified in other NCC-derived tissues in ca-Acvr1(A11) mutants, such as in cardiac neural crest-derived tissues of the heart (27) and trunk neural crest-derived dorsal root ganglion (DRG) of the peripheral nervous system in association with elevated pSmad1/5/9 and cell death (Supplemental Figure 8, A-D). Similarly, elevated BMP signaling downregulated the histone lactylation and PDGFRA expression in cardiac and trunk neural crest derivatives in vivo (Supplemental Figure 8, E and F).…”

Osteoclast differentiation and dynamic mRNA expression during mice embryonic palatal bone development

“…8). Transgenic mice are often used to investigate the role of a gene in palate development by altering its expression at specific time points and tissues [36][37][38] . Therefore, the study of the time and site of OCL differentiation in embryonic palatal bone can be the basis for further research.…”