Gert Helge Hansen

Small intestinal absorptive cells, enterocytes, lead a short but busy life.
Generated in the proliferative regions of the crypts of Lieberkühn, enterocytes migrate upwards to the top of the villi from where they are extruded into the gut lumen after a life-span of only 3-6 days. Within this period, they rapidly differentiate into mature cells in preparation for their main function: to digest and assimilate nutrients from the diet. A key element in this process is to generate and maintain an extensive luminal brush border membrane capable of acting as a digestive/absorptive surface. In addition, enterocytes are continuously engaged in transcytosis of IgA, providing local, luminal immunity. Together, these functions require a complex network of apical membrane trafficking routes in which a subapical endosomal compartment may serve as a central hub interconnecting the brush border, the TGN, the basolateral cell surface, and lysosomes.

We are interested in all aspects of apical trafficking and are currently focusing our work on the function of lipid "rafts" in this complex process.

It has been known for more than a decade that sphingolipids and cholesterol together can form microdomains (commonly termed "rafts") in the exoplasmic leaflet of cell membranes. Such rafts are thought to exist as ordered membrane patches surrounded by more fluid membrane mainly composed of glycerolipids. By acting as lateral platforms for specific subsets of proteins, rafts have been proposed to function in apical membrane trafficking in epithelial cells. At the cell surface rafts sometimes appear as caveolae (small flask-shaped membrane invaginations). Here, they are believed mainly to function in endocytosis and signal transduction events, but new raft components -and functions are frequently being reported. Thus, although the raft concept originated as a narrow speciality within membrane biology, "raftology" by now has re-defined our classical view of cell membranes and is rapidly expanding into other fields of cell biology and biomedicine.