Abstract
Acquisition of cell polarization is essential for the performance of crucial functions, like a successful secretion and appropriate cell signaling in many tissues, and it depends on the correct functioning of polarity proteins, including the Crumbs complex. The CRB proteins, CRB1, CRB2 and CRB3, identified in mammals, are expressed in epithelial-derived tissues like brain, kidney and retina. CRB2 has a ubiquitous expression and has been detected in embryonic brain tissue; but currently there is no data regarding its localization in the adult brain. In our study, we characterized the presence of CRB2 in adult mice brain, where it is particularly enriched in cortex, hippocampus, hypothalamus and cerebellum. Double immunofluorescence analysis confirmed that CRB2 is a neuron-specific protein, present in both soma and projections where colocalizes with certain populations of exocytic and endocytic vesicles and with other members of the Crumbs complex. Finally, in the cortex of CRB1rd8 mutant mice that contain a mutation in the Crb1 gene generating a truncated CRB1 protein, there is an abnormal increase in the expression levels of the CRB2 protein which suggests a possible compensatory mechanism for the malfunction of CRB1 in this mutant background.
Highlights
Cell polarity is achieved through the coordinated functions of three evolutionarily conserved polarity complexes: Crumbs and Par and Scribble[1,2,3]
The immunohistochemistry analysis showed that in the hypothalamus, CRB2 was found concentrated in particular cell bodies, which were mainly located in specific areas such as the Periventricular Nucleus (PVN), Dorsomedial Hypothalamic Nucleus (DMH), Ventromedial Hypothalamic Nucleus (VMH) and the Retrochiasmatic part of the Supraoptic area (SOR) (Fig. 1B)
Besides the nuclear staining, the immunofluorescence analysis showed a distinctive punctate CRB2 labeling that seemed to be accurately arranged between the Hypothalamic Dorsal Area (DA) and the SOR region (Fig. 1C, yellow arrowheads)
Summary
Cell polarity is achieved through the coordinated functions of three evolutionarily conserved polarity complexes: Crumbs and Par (apical complexes) and Scribble (basal complex)[1,2,3]. The intracellular domain of CRB, the sole transmembrane member of the complex, establishes a scaffolding complex with other members of the Crumbs, Par and Scribble complexes, essential for the correct accomplishment of all these activities[3,7,8]. The formation of these specialized cell surface domains and the acquisition of cell polarity is highly dependent on the transport and docking of the polarity proteins towards their appropriate locations in the plasma membrane. It has been reported that mutations in the Crb[2] gene produce a phenotype resembling congenital nephrosis with cerebral ventriculomegalia[35], suggesting this phenotype could be related with a ciliopathy[36]
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