Gli1 is not required for Pdgfralpha expression during mouse embryonic development.
Pdgfra is expressed in the mesenchyme of multiple organs during embryonic development and Pdgfralpha is involved in cell proliferation, differentiation, migration, and apoptosis in many tissues. A fine-tuned regulation of gene transcription is required to achieve these effects. To investigate if the Shh signaling pathway is involved in the tightly regulated Pdgfra expression during embryogenesis, we systematically compared Gli1 and Pdgfralpha mRNA expression patterns in vivo from mouse embryonic day 9.5 to 14.5. We found that an initial partly overlapping expression of Gli1 and Pdgfralpha in the mesenchyme of foregut and somites was changed to different expression patterns when the mesenchyme differentiated into specialized structures such as intestinal villi and chondrocytes. Gli1 and Pdgfra were also expressed differently in the developing lung, heart, central nervous system, skin, tooth, and eye. Importantly, neither Pdgfralpha mRNA patterns nor levels were altered in Ihh mutant embryos although Gli1 and Ptc mRNA levels were dramatically reduced. Our results demonstrate that Gli1 is not required to induce Pdgfra expression during embryonic bone development, and are consistent with previous findings that Pdgfralpha and Hh pathways serve different functions in, e.g., bone, gut, and lung development. However, we cannot exclude the possibility that Glis can have more complex regulatory effects on Pdgfra gene activity, nor can we exclude such effects in pathological conditions.