Abstract
Abstract: :
Purpose: We showed previously that the teleost retina is a target tissue of systemic GH, which acts to regulate the persistent, growth–associated neurogenesis in this tissue (Otteson et al., Mech. Develop. 2002, 117:137–149). Exogenous GH elevates IGF–I synthesis in the retina and stimulates proliferation of retinal stem cell and progenitors. The study described here was undertaken to identify the cells in the teleost retina that express the GH receptor. Methods: Using standard PCR techniques, a 1.8 Kb cDNA corresponding to the entire coding sequence of goldfish growth hormone receptor was isolated and cloned from retinal RNA. In situ hybridization combined with tyramide signal amplification was used to identify cells expressing the GH receptor in the retina of the goldfish. Results: Sequence analysis showed that the clone isolated from retina was identical to the goldfish GH receptor isolated from liver (Lee et al., Gene. 2001 270:121–129). The in situ hybridization revealed that the GH receptor is expressed by retinal progenitors in the circumferential germinal zone (CGZ) and differentiated cells within the inner nuclear layer. Conclusions: These data demonstrate that the GH receptor is expressed in the teleost retina. Also, these data suggest that cells expressing the GH receptor synthesize IGF–I and their response underlies the GH–stimulated upregulation in IGF–I synthesis. Finally, expression of the GH receptor by retinal progenitors in the CGZ suggests that GH may be directly mitogenic for these cells.
Keywords: retinal development • growth factors/growth factor receptors • gene/expression