Abstract
BACKGROUND: All‐trans‐retinoic acid (RA) can produce branchial arch abnormalities in postimplantation rodent embryos cultured in vitro. Platelet‐derived growth factor C (PDGF‐C) was recently identified as a member of the PDGF ligand family. Many members of the PDGF family are essential for branchial arch morphogenesis and can be regulated by RA. The roles of PDGF‐C in branchial arch malformations induced by RA and possible mechanisms were investigated. METHODS: In whole embryo culture (WEC), mouse embryos were exposed to RA at 0, 0.1, 0.4, 1.0, or 10.0 μ__M__, PDGF‐C at 25, 50, or 75 ng/mL, or PDGF‐C at 25, 50, or 75 ng/mL containing 0.4 μ__M__ RA. After 48 h of culture, mouse embryos were examined for dysmorphogenesis, and whole‐mount immunohistochemistry was applied to PDGF‐C. In explant cultures, explants were exposed to the same doses of RA and PDGF‐C as WEC. Semiquantitative RT‐PCR, zymography, and reverse zymography were used to evaluate the expressions and activities of matrix metalloproteinase (MMP)‐2, MMP‐14, and tissue inhibitor of metalloproteinase (TIMP)‐2. RESULTS: PDGF‐C was reduced by RA, and exogenous PDGF‐C rescued the branchial arch malformations induced by RA. Moreover, PDGF‐C prevented RA‐induced inhibition of the migratory ability of mesenchymal cells in the first branchial arch, by regulating the expressions of MMP‐2, MMP‐14, and TIPM‐2. CONCLUSIONS: Our results suggest that RA exposure reduces the expression of PDGF‐C. The branchial arch malformations resulting from fetal RA exposure are caused at least partially by loss of PDGF‐C and subsequent misregulations of the expressions of MMP‐2, MMP‐14, and TIMP‐2. Birth Defects Research (Part A), 2007. © 2006 Wiley‐Liss, Inc.