Purpose: Platelet-derived growth factor (PDGF) has previously been shown to influence lens growth and transparency. The purpose of the present study was to investigate the expression of the PDGF receptor and its mRNA during lens development in chicken embryos.
Methods: To examine the expression of PDGF receptor mRNAs, the authors used a combination of polymerase chain reaction, Northern blot analyses, and RNase protection assays. Platelet-derived growth factor receptors were studied using Western blot analyses and immunofluorescence-confocal microscopy. The mitogenic effects of PDGF were assayed using immunochemical detection of 5-bromo-2'-deoxyuridine incorporation into explanted lens epithelia.
Results: The authors' studies strongly suggest that the PDGF alpha receptor is the only PDGF receptor present in the embryonic chicken lens during development because they were unable to detect the PDGF beta receptor using two different approaches. Northern blots showed that the chicken lens alpha receptor mRNA is similar in size to the mRNA encoding the human and frog alpha receptor, and Western blots detected a single band with a molecular weight of 170 kDa, close to the reported molecular weight for the human alpha receptor. After staining with specific antibodies, confocal microscopy localized the immunoreactivity to the membranes of the epithelial and annular pad cells. At early stages of development (E6), the PDGF alpha receptor was present throughout the epithelium. At later stages, immunoreactivity was restricted to the peripheral epithelium and the annular pad. The addition of human recombinant PDGF (AA or BB) to tissue cultured E6 chicken lens epithelia sustained cell proliferation significantly better than basal medium alone.
Conclusions: The authors' studies provide the first evidence for PDGF alpha receptors in the chicken lens. Localization of these receptors to the peripheral lens epithelium during development and the mitogenic effect of exogenously added PDGF suggest a role for this growth factor in the control of lens growth.