SPATIOTEMPORAL DISTRIBUTION OF SPARC OSTEONECTININ DEVELOPING AND MATURE CHICKEN RETINA/

Expression of SPARC (Secreted Protein, Acidic, Rich in Cysteine), a co unteradhesive, calcium-binding extracellular matrix (ECM) glycoprotein , is associated with several morphogenetic events during early develop ment. In this study, changes in the spatiotemporal distribution of SPA RC transcripts and the protein during chicken retinal development were documented by in situ hybridization and indirect immunofluorescence m icroscopy. SPARC transcripts were first detected within the proliferat ing neural ectoderm at embryonic day 4.5 (E4.5), followed short therea fter (E5) by appearance of SPARC. SPARC was enriched within the inner plexiform layer (IPL) by E10 and within the outer plexiform layer (OPL ) by E14, several days after these layers became morphologically disti nct. Significant levels of SPARC transcripts were first observed withi n the ganglion cell layer (GCL) at E17 prior to accumulation of SPARC within the nerve fiber layer, seen first at E20. SPARC protein was fir st detected within the developing retinal pigment epithelium (RPE) at E10 and increased significantly at RPE cells ceased to proliferate and continued differentiating. Of special note was the restriction of SPA RC to the basal-half of the RPE cells. SPARC transcripts were similarl y distributed in the adult retina, but at lower levels than in the per iod just prior to hatching. In the adult retina SPARC was retained in the nerve fiber layer and present in the inner nuclear layer (INL) and outer nuclear layer (ONL), but lost from the IPL and OPL. These chang es in expression pattern with time indicate that SPARC is developmenta lly regulated and therefore may have important function(s) in both mor phological development of the retina and functioning of the mature eye . (C) 1997 Academic Press Limited.