Differential expression of decorin and biglycan genes during palatogenesis in normal and retinoic acid–treated mice

Abstract

Proteoglycans are involved in secondary palate formation. In the present study, we focused on two small leucine-rich proteoglycans, decorin and biglycan, because they assembled extracellular matrix molecules such as collagens and modulated signaling pathway of transforming growth factor-␤. To investigate the functions of decorin and biglycan in palatogenesis, we compared their mRNA expression patterns between normal palate and retinoic acid-induced cleft palate in mice by using in situ hybridization analysis during the period of embryonic day 13.5 (E13.5) to E15.5. On E13.5, decorin mRNA was expressed in the epithelia and mesenchyme on the nasal side of the developing secondary palate. During the period the palate shelves were fusing (E14.5), decorin mRNA was strongly expressed in the mesenchyme but its expression pattern was asymmetric; decorin mRNA expression area in the nasal side was broader than that in the oral side. The expression of decorin mRNA was hardly detected in the mesenchyme on either side of the medial edge epithelium. After fusion (E15.5), its expression converged to the mesenchyme just around the palatine bone. Biglycan mRNA was ubiquitously distributed throughout the palatal mesenchyme for the mid-gestation period. Its expression area became limited to the ossification area within the palate after the late gestation period. In the retinoic acid-treated mice, the area of the decorin gene expression expanded to the core region of the palate primordium where little signal was observed in control mice. On the other hand, biglycan in the retinoic acid-treated mice did not show remarkable change in its distribution patterns compared with that in the control mice. These findings suggest that decorin and biglycan play distinct roles in palatogenesis, and decorin was more actively involved in the process of secondary palate formation than biglycan. Up-regulation of decorin gene expression in the retinoic acid-treated mice might influence the pathogenesis of cleft palate. Developmental Dynamics 226:618 -626, 2003.

Cleft Palate Cells Can Regenerate a Palatal Mucosa in vitro

“…It can also modulate the signaling pathway of TGF-␤ (Yamaguchi et al, 1990;Hildebrand et al, 1994), which is also important in organ development (Kingsley, 1994). In retinoic acid-induced cleft palate, decorin expression was increased (Zhang et al, 2003). In the present study, the expression of decorin was similar in both mucosal substitutes, and also similar to the levels in native mucosa.…”

Retinoic acid alters the proliferation and survival of the epithelium and mesenchyme and suppresses Wnt/β-catenin signaling in developing cleft palate

“…Thus, we used 70 mg/kg RA 15, 16 at E12. Consistent with our expectation, the 100% of fetuses showed cleft palate with litter death and few other malformations (Supplementary Table S1).…”

Vitamin A and clefting: putative biological mechanisms

“…The shelves increase in size by mesenchymal cell proliferation and by the production and hydration of extracellular matrix (ECM) components 28 . In pregnant mice, RA overexposure reduces the growth of the palatal shelves in the embryo 33 . This seems to be a consequence of reduced mesenchymal cell proliferation as well as inhibition of ECM production 34,35 .…”

“…During palatogenesis, downregulation of PDGF signaling by RA results in hypoplastic palatal shelves that are not able to fuse, 39 probably due to inhibition of nuclear regulator genes that control cell proliferation, such as members of the signal transducer and activator or transcription family and nuclear factor κB 41 . Moreover, RA stimulates expression of the small proteoglycan decorin, which might inhibit mesenchymal proliferation 33 . In several cell types, decorin activates the epidermal growth factor receptor (EGFR) that induces activation of mitogen‐activated protein kinases, mobilization of intracellular calcium, upregulation of p21, and, finally, growth suppression 42 …”

“…Another mechanism involves RA‐induced decorin, which binds to collagen and thereby stimulates collagen fiber assembly 61 . This might enhance the stiffness of collagen fibers and prevent elevation 33 . In human as well as murine mesenchymal cells, RA inhibits the synthesis of GAGs, 34,55,62 possibly by interference with the p38 mitogen‐activated protein kinase pathway in TGF‐β1 and ‐2 signaling 63,64 .…”