Redistribution of insoluble interphotoreceptor matrix components during photoreceptor differentiation in the mouse retina

Abstract The development of the nervous‐system is largely influenced by the extracellular matrix (ECM). In the neural retina, the photoreceptors are surrounded by a unique ECM, the interphotoreceptor matrix (IPM). The IPM plays a central and possibly crucial role in the development, maintenance and specific function of the photoreceptors. Therefore, the characterization of IPM components is necessary to understand the mechanisms regulating photoreceptor differentiation. The IPM in the mouse retina was examined during photoreceptor morphogenesis with the monoclonal antibody (MAb) F22, which recognizes a 250 kDa component of the interphotoreceptor matrix. The binding pattern of MAb F22 revealed a striking redistribution in the expression of the 250 kDa F22 antigen in late stage of postnatal photoreceptor differentiation in the mouse retina. The F22 staining was detectable in the IPM around the inner segments on the third postnatal day (P3). The MAb F22 initially labeled the region around inner segments, but as the outer segments elongated, the F22 distribution became concentrated to the matrix around the rod and cone outer segments until P16–17. At P17, the F22 label around rods began to disappear, while the label around cones became more defined. The shift in label distribution was largely completed by P20. Residual rod‐associated label disappeared within a few days. In the adult animal, the F22 antibody labeled the cone‐associated matrix only, and this labeling pattern remained stationary. The change in the distribution of MAb F22 demonstrated by immunolabeling was not accompanied by changes in the size of the molecule; F22 antigen isolated from the IPM of P13–15, and from adult IPM migrated with the same molecular weight on SDS gels. The distribution of MAb F22 was compared to that of chondroitin sulfate proteoglycans which are abundant in the IPM. The labeling patterns of MAbs CS‐56, C6‐S and C4‐S were distinct from that of MAb F22. A general decrease of the label intensity was seen with two chondroitin sulfate MAbs (CS‐56 and C4‐S) between 16 days and 4 months, but a total loss of rod‐associated label was not observed. All three chondroitin sulfate MAbs labeled the retina at embryonic day (E) 11.5–13.5, a time of outgrowth of ganglion cell axons, but the F22 antigen was not detected in the retina at this stage of development. The results demonstrate that the F22 and the chondroitin sulfate antibodies are recognizing different molecules that have distinct roles in retinal morphogenesis. The expression of the F22 antigen was temporally correlated with photoreceptor outer segment differentiation. The redistribution of F22 label at P17–20 occurred at the end of the developmental period and suggests that the F22 antigen could have different roles, both in photoreceptor differentiation, and in the mature retina. © Wiley‐Liss, Inc.