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A.V. Kantardzhieva, J. Klooster, J. Wijnholds; Crumbs1 and Maguk protein MPP4 in Retinitis Pigmentosa . Invest. Ophthalmol. Vis. Sci. 2004;45(13):4720.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:Establishment and maintenance of photoreceptor cell polarity is regulated by members of the membrane associated guanylate kinase (MAGUK) and Crumbs homologue 1 (CRB1) families. This study examined the subcellular distribution and physical interaction of CRB1 and membrane palmitoylated protein 4 (MPP4). Methods:The cDNAs for human CRB1, and mouse and human MPP4 were cloned and sequenced. Antibodies raised against MPP4 and CRB1 were used to determine the subcellular localization of the proteins by immuno–electron microscopy, immunofluorescence, and confocal laser scanning microscopy. Physical interaction between the two proteins was examined by immunoprecipitation studies. Results:Human and mouse CRB1 and MPP4 were localized apical to the outer limiting membrane (OLM). The majority of MPP4 was present in the outer plexiform layer (OPL). Ultra structural analysis by immuno–electron microscopy showed the presence of Mpp4 around the adherence junction and neighboring trans Golgi network, and in the synaptic terminals of photoreceptor cells, where it was at the basal and lateral membrane contacts of cones, and mostly lateral in rod spherules. The protein was associated with vesicles proximal to the pre–synaptic membrane. Immunoprecipitation studies indicated that MPP4 and CRB1 form a protein complex. Conclusions:MPP4 and CRB1 co–localize apical to the outer limiting membrane of photoreceptors, and form a multiprotein complex. The two proteins are likely to be involved in common biochemical and functional pathways in the OLM of photoreceptor cells. The localization of MPP4 in more than one site in the photoreceptors points to participation in more than one complex of proteins and more than one function.
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