Plays a role in photoreceptor morphogenesis in the retina (PubMed:12915475). May maintain cell polarization and adhesion (PubMed:15316081). May play a role in epidermal tissue morphogenesis (PubMed:14684155). May function in cell attachment for stratified epithelial organization (PubMed:14684155). Component of a complex composed of PALS1, CRB1 and EPB41L5 (By similarity). Within the complex, interacts (via intracellular domain) with PALS1 and EPB41L5 (via FERM domain) (By similarity). Forms a complex with MPP4 and PALS1 (PubMed:15316081). Interacts with MPDZ/MUPP1 and MPP4 (PubMed:15316081). Found in the cytoplasmic area of undifferentiated keratinocytes and associated with the plasma membrane at the site of cell-cell contacts and focal adhesion upon keratinocytes differentiation. Expressed in the kidney, lung, stomach and testis (PubMed:14684155). Expressed in the brain (PubMed:11744384, PubMed:14684155). Expressed in the retina of the eye (PubMed:11744384, PubMed:14684155, PubMed:26404741). Expressed in the outer nuclear layer, photoreceptor layer and inner nuclear layer of the retina (PubMed:11744384). Expressed in Mueller cell radial processes in the inner nuclear layer, in apical processes sclerad to the external limiting membrane, and in the subapical region, adjacent to the adherens junction of retinal photoreceptors (PubMed:12915475, PubMed:15316081). In the brain, expressed in the granular layer of the cerebellum, the hippocampal dentate gyrus, the olfactory bulbs, the subventricular region lining the telencephalic ventricles and the rostral migratory stream (PubMed:11744384). Ubiquitously expressed. Primarily detected in the central nervous system at 10.5 dpc, in the ventral part of the neural tube including the ventral spinal cord, the ventral part of the mesencephalon, the mammillary and the hypothalamic regions, the optic area and the zona limitans intrathalamica (PubMed:11744384). Expressed by the V3 interneurons placed between the floor plate and the motorneurons all along the spinal cord axis (PubMed:11744384). In late embryogenesis, expressed mainly in ventral neural structures of the developing brain, including the mammillary, tuberalis regions of the hypothalamus and the preoptic area (PubMed:11744384). Starting from 12.5 dpc, also strongly expressed in the neural area that gives rise to the dorsal thalamus (PubMed:11744384). In the retina, expression starts at 11.5 dpc and is enhanced at 12.5, 14.5 and 16.5 dpc (PubMed:11744384). Expressed in the subapical region of the neuroepithelial layer of the retina at 17.5 dpc (PubMed:23001562). In postnatal stages, abundant expression in photoreceptors and also found in the inner nuclear layer and iris (PubMed:11744384). Expression first detected at 14 dpc, expression is enhanced at 15 and 16 dpc during active proliferation of epidermal cells, decreases after birth, but is maintained in adult skin (PubMed:14684155). Detected in the skin basal cells at 16 dpc, it was observed in upper layers after birth (at protein level) (PubMed:14684155). Glycosylated. Defects in Crb1 are a cause of focal retinal dysplasia and degeneration associated with a shortening of inner and outer segments. Affected mice produce a secreted truncated protein that lacks the single transmembrane and the intracellular domain, and develop irregularities at the outer limiting membrane and loss of photoreceptor cells. Belongs to the Crumbs protein family.