Abstract
Expression of the platelet-derived growth factor A-chain gene (Pdgfa) occurs widely in the developing mouse, where it is mainly localized to various epithelial and neuronal structures. Until now, in situ mRNA hybridization (ISH) has been the only reliable method to identify Pdgfa expression in tissue sections or whole mount preparations. Validated protocols for in situ detection of PDGF-A protein by immunohistochemistry is lacking. In particular, this has hampered understanding of Pdgfa expression pattern in adult tissues, where ISH is technically challenging. Here, we report a gene targeted mouse Pdgfa allele, Pdgfaex4 COIN, which is a combined conditional knockout and reporter allele. Cre-mediated inversion of the COIN cassette inactivates Pdgfa coding while simultaneously activating a beta-galactosidase (lacZ) reporter under endogenous Pdgfa transcription control. The generated Pdgfaex4 COIN-INV-lacZ allele can next be used to identify cells carrying a Pdgfa null allele, as well as to map endogenous Pdgfa expression. We evaluated the Pdgfaex4 COIN-INV-lacZ allele as a reporter for endogenous Pdgfa expression patterns in mouse embryos and adults. We conclude that the expression pattern of Pdgfaex4 COIN-INV-lacZ recapitulates known expression patterns of Pdgfa. We also report on novel embryonic and adult Pdgfa expression patterns in the mouse and discuss their implications for Pdgfa physiology.
Highlights
The platelet-derived growth factor (PDGF) family plays fundamental roles during several stages of vertebrate development
The Pdgfaex4COIN allele was expected to be functional, since splicing between exons 4a and 4b resulted in an RNA sequence identical to that encoded by the original exon 4
Exon 4-encoded sequences are absolutely required for the production of a functional PDGF-A protein, and this splicing event is necessary for the functionality of the Pdgfaex4COIN allele
Summary
The platelet-derived growth factor (PDGF) family plays fundamental roles during several stages of vertebrate development The mammalian PDGFs encompass 5 protein isoforms, which are dimers of 4 distinct, but related, polypeptide chains (PDGF-A-D) encoded by separate genes. Whereas ligand-receptor interactions mapped in vitro suggest a significant degree of redundancy in PDGF ligand-receptor interaction, in vivo gene knockout analyses show that PDGF-AA and PDGF-CC are the principal ligands for PDGF-Ra, at least during development, whereas PDGF-BB is the key ligand for PDGF-Rb [3,4,5,6,7]. The developmental roles of PDGFs mapped to-date suggest paracrine modes of signaling, i.e. PDGFs released from one type of cells act on neighbors of a different type Various developing epithelia express PDGF-A and PDGF-C, whereas the neighboring mesenchyme expresses PDGF-Ra [9–
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