Transforming growth factor alpha and its receptor in neural retina

Transforming growth factor alpha (TGF-alpha) stimulates mitosis of many ectodermal cells but has not previously been studied for its role in neural tissues such as retina. We examined bovine retina for the presence of TGF-alpha mRNA, TGF-alpha protein and for the presence and location of the TGF-alpha/EGF receptor. Biochemical studies demonstrated a high level (770 fmol/mg protein) of specific, high affinity (Kd = 2 nM) TGF-alpha/EGF receptors in membrane homogenates of neural retina, but undetectable binding to homogenates of retinal pigment epithelium. Light microscopic autoradiograms of sections of neural retinal tissue incubated with 125I-EGF indicated that specific TGF-alpha/EGF receptors were present on one or more cell types of the retina with the exception of the outer segments of the photoreceptor cells. In addition, retinal cells appear to synthesize TGF-alpha since both mRNA for TGF-alpha and TGF-alpha protein (4.2 ng/mg protein) were detected in retinal extracts using cDNA hybridization and TGF-alpha RIA techniques. The role(s) of TGF-alpha and its receptor in retina is unknown, but it is possible that they interact via an autocrine/paracrine mechanism to influence retinal regeneration, proliferative retinopathies or neural transmission.