VIP17/MAL, a lipid raft-associated protein, is involved in apical transport in MDCK cells

Apical proteins are sorted and delivered from the trans-Golgi network to the plasma membrane by a mechanism involving sphingolipid–cholesterol rafts. In this paper, we report the effects of changing the levels of VIP17/MAL, a tetraspan membrane protein localized to post-Golgi transport containers and the apical cell surface in MDCK cells. Overexpression of VIP17/MAL disturbed the morphology of the MDCK cell layers by increasing apical delivery and seemingly expanding the apical cell surface domains. On the other hand, expression of antisense RNA directed against VIP17/MAL caused accumulation in the Golgi and/or impaired apical transport of different apical protein markers, i.e., influenza virus hemagglutinin, the secretory protein clusterin (gp80), the transmembrane protein gp114, and a glycosylphosphatidylinositol-anchored protein. However, antisense RNA expression did not affect the distribution of E-cadherin to the basolateral surface. Because VIP17/MAL associates with sphingolipid–cholesterol rafts, these data provide functional evidence that this protein is involved in apical transport and might be a component of the machinery clustering lipid rafts with apical cargo to form apical transport carriers.

Retinal engineering: engrafted neural cell lines locate in appropriate layers.

A major question in central nervous system development, including the neuroretina, is whether migrating cells express cues to find their way and settle at specific locations. We have transplanted quail neuroretinal cell lines QNR/D, a putative amacrine or ganglion cell, and QNR/K2, a putative Müller cell into chicken embryo eyes. Implanted QNR/D cells migrate only to the retinal ganglion and amacrine cell layers and project neurites in the plane of retina; in contrast, QNR/K2 cells migrate through the ganglion and amacrine layers, locate in the inner nuclear layer, and project processes across the retina. These data show that QNR/D and QNR/K2 cell lines represent distinct neural cell types, suggesting that migrating neural cells express distinct address cues. Furthermore, our results raise the possibility that immortalized cell lines can be used for replacement of specific cell types and for the transport of genes to given locations in neuroretina.