Localization of prominin-1 in the retina of mice

CASTAÑEDA M; TORBIDONI V; IRIBARNE M; SUBURO AM

Buenos Aires

Congreso; XVII International Congress of Eye Research (ICER); 2006

Internationational Society of Eye Research

PURPOSE: Prominin-1 (PROML1, CD133) is a pentaspan membrane glycoprotein expressed on the surface of several somatic stem cells, including endothelial and hematopoietic progenitors and neuroepithelial cells. Prominin-1 is specifically associated with plasma membrane protrusions, irrespective of the cell type. It is not known whether prominin plays a significant role in key stem cell functional features. However, the AC133 epitope is currently used as a marker for the isolation of adult stem or progenitor cells. Fragments of the AC133 gene have been cloned from adult retina, and a late onset human autosomal recessive retinal degeneration has been associated to a nucleotide 1878 deletion in PROML1 . Therefore, we have now studied the distribution of prominin-1 immunoreactivity in the retina of adult mice. METHODS: Male Balb-c mice were bred under a constant cycle of 12 hours light/ 12hours dark, with basal illumination levels not exceeding 60 lux. They were perfused through the ventricle with 4% paraformaldehyde. Eyes were enucleated, cryoprotected and cryosectioned. Immunoenzymatic and double immunofluorescent assays were made, using a rat monoclonal antibody against prominin-1 (Anti-CD133, clone 13A4, MAB4310X) and a rabbit polyclonal serum against glutamine-synthase. RESULTS: Immunoenzymatic procedures showed that PROML1-immunoreactivity appeared both in the outer and inner retina. In the outer retina, short filiform structures were strongly immunostained. These structures formed a distinct stripe along the inner aspect of the outer segments layer. Their shape and localization suggests that PROML1-immunoreactivity would be localized in the ciliary calyx, a ring of microvilli that project from the distal end of the inner segment and surround both the connecting cilium and the proximal end of the outer segment. In the inner retina, PROML1-immunoreactivity was found in radial processes with the typical structure of Müller cells. These processes appeared both in central and peripheral regions of the retina and their identity was demonstrated by co-localization with glutamine synthase. CONCLUSIONS: The presence of PROML1 in photoreceptor calycal processes has been previously described in neonatal and adult mice. This localization resembles the association of PROML1 with membrane protrusions and could probably be involved in the generation of new outer segment disks. However, this is the first description of PROML1 in adult Müller cells from non-injured retinas. Although Müller could perhaps behave as stem cells, this localization is surprising, since PROML1 has not been detected in neuroepithelial cells from neonatal mice.