Platelet-derived growth factor B (PDGF-B) belongs to the mitogen and growth factor family and like the other members it has many roles in cell differentiation, proliferation and migration during development, adult life and in pathological conditions. Among them it has been observed that aberrant PDGF signalling is frequently linked to glioma development and progression, and Pdgf-b over-expression in mouse neural progenitors leads to the formation of gliomas. Despite this evidence, the mechanisms underlying PDGF-B driven tumorigenesis and its role during brain development are not fully understood. In order to contribute to clarifying possible new roles of pdgf-b signalling, we present here the embryonic gene expression pattern of pdgf-b, so far unknown in early vertebrate development. By using Xenopus laevis as a model system we performed qRT-PCR and whole mount in situ hybridization. Pdgf-b mRNA is expressed in discrete regions of the developing central nervous system, in the cranial nerve placodes and in the notochord. We also compared the gene expression of pdgf-b with that of its receptor pdgfr-a suggesting so far unsuspected roles for this signalling pathway during the development of specific embryonic structures.
KEY WORDS: PDGF-B, PDGF receptor a, central nervous system, neural crest, Xenopus laevisPlatelet-derived growth factor (PDGF) family comprises two tyrosine kinase receptors (PDGFR-a and -b) and four ligands (PDGF-A, -B, -C, and -D) that form homodimers or the heterodimer AB (Demoulin and Essaghir, 2014). The active ligand-receptor complex consists of two receptor chains associated with one dimeric ligand. While PDGFR-a binds to all PDGF isoforms except for PDGF-DD, PDGFR-b binds only to PDGF-BB and -DD (Fig.1). Also a heterodimeric ab receptor has been reported that binds to PDGF-AB, -BB and possibly -CC and -DD (Demoulin and Essaghir, 2014). The members of this family have been extensively studied for more than 30 years in development, adult homeostasis and disease (Heldin, 2013, Heldin, 2014, Hoch and Soriano, 2003. Pdgf-a expression was recently characterized in mouse tissues and in early embryonic development, showing its involvement in developmental processes including gastrulation and craniofacial development (Andrae et al., 2014, Eberhart et al., 2008. On the contrary, for pdgf-b the only information available mainly concern its role during embryonic angiogenesis (Hoch and Soriano, 2003, Leveen et al., 1994), and a complete gene expression pattern in vertebrate embryogenesis is still lacking. Functional studies using a knock out mouse for pdgf-b showed abnormal kidney glomeruli, heart and blood vessel dilation, anemia, thrombocytopenia, haemorrhages and perinatal death (Betsholtz, 1995, Leveen et al., 1994. However, in this mutant line, BB homodimer and AB heterodimer were simultaneously abrogated, making difficult to precisely define the specific role of pdgf-b alone during embryogenesis. Furthermore, due to extensive perinatal haemorrhages, other possible phenotypes caused by the...