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Neuron-Glia Interactions in Health and Disease
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CRUMBS > Current Knowledge > CRB2 and CRB3

Studies on the cellular function of the CRB1-homologues CRB2 and CRB3

 CRB2

Crb2 is another vertebrate homologue of Drosophila crumbs. It is situated on human chromosome 9. Crb2 has a similar protein structure as CRB1 as it also contains a signal peptide, 3 laminin A/G-like domains flanked by EGF-like domains in the extracellular part of the protein, transmembrane domain, and the short 37 amino acid cytoplasmic domain. Crb2 is expressed in more tissues than Crb1 in both the embryo and adult. In the adult, it is expressed in the brain, kidney, retina, RPE/choroid, bladder, lung, placenta and heart . A recent study (van den Hurk et al. 2005) suggests that it is unlikely that variants in the CRB2 sequence causes autosomal recessive RP and LCA. However, the fact that Crb2 is expressed in a large number of tissues means that it is possible that mutations in Crb2 may effect several organ structures.

Crb2 expression at the RNA (left) and protein (right) level in the embryonic mouse eye.

Figure 10: Crb2 expression at the RNA (left) and protein (right) level in the embryonic mouse eye (equivalent to ~ 5 weeks gestation in the human).

CRB3

Crb3 is another Crumbs homologue but it has a very short extracellular domain without EGF and Laminin repeats and it is expressed in all epithelial tissues and in the retina in particular. The presence of Crb2 and Crb3 in the retina might protect patients by providing a normal morphogenesis of the eye and retina but later during life, defects in Crb1 function induce retina degeneration despite the expression of the two other Crb genes and proteins.