Wolfgang Baehr
Professor of Ophthalmology and of Neurobiology & Anatomy and of Biology
Diploma University of Heidelberg, Germany
Ph.D. University of Heidelberg, Germany
Wolfgang Baehr's Lab Page
Wolfgang Baehr's PubMed Literature Search
Research
Rod and cone photoreceptors have evolved into highly polarized structures consisting of three distinct areas: the outer segment containing membrane disks housing proteins involved in phototransduction, the inner segment where biosynthesis occurs, and the synaptic terminal that transmits excitation by light to downstream neurons. The inner segment (cell body) connects to an outer segment through a narrow 9+0 cilium, and to the synaptic terminal by a slender axon. Outer segments of rods and cones are renewed roughly every ten days. New disks are made at the proximal end, old disks are shed at the distal end, and phagocytosed by the adjacent retinal pigment epithelium (RPE). Daily renewal of ~10%(about 100 disks) of the outer segment membrane requires a high rate of biosynthesis to replace OS proteins, with reliable transport and targeting pathways.
My laboratory explores mechanisms in membrane protein transport in mammalian rod and cone photoreceptors, specifically post-biosynthesis transport of integral membrane and peripheral membrane-associated proteins to the outer segments for disk assembly. Integral membrane proteins are synthesized by ER-associated ribosomes and exported to the Golgi apparatus. Peripheral membrane proteins are synthesized in the cytosol and become ER-associated if prenylated or acylated. Vesicles emerge from the trans-Golgi network (TGN) and transport to the base of the cilium where they fuse with the cell membrane. Finally, cargo is assembled for intraflagellar transport to the outer segment where phototransduction occurs.
We are interested in proteins/genes mediating transport, particularly molecular motors (kinesin), small GTP binding proteins (rab8), prenyl binding proteins mediating transport of prenylated proteins (PrBP/delta or PDE6D), acyl binding proteins (UNC119) involved in transport of G protein subunits, and centrins, small Ca2+ binding proteins involved in ciliogenesis. We produce knockouts/knockins, transgenics, and tissue culture to monitor consequences of knockouts, dominant negative transgenes, or short hairpin RNAi. Most frequently applied techniques are standard biochemistry/molecular biology, confocal and electron microscopy, electroretinography (photoreceptor function), optomotry (behaviour), and in-vivo electroporation (transfer of genes into neonatal retina), and gene therapy (AAV virus).
Cartoon of transport vesicle “schlepping” peripheral and integral membrane proteins to the photoreceptor outer segment along microtubules serving as highways. The “truck” in this cartoon is kinesin -2, a molecular motor involded in anterograde transport.
References
1. Zhang H, et al. (2007) Deletion of PrBP/δ impedes transport of GRK1) and PDE to photoreceptor outer segments. Proceedings of the National Academy of Sciences USA 104:8857-62
2. Baehr W, et al. (2007) The function of Guanylate Cyclase 1 (GC1) and Guanylate Cyclase 2 (GC2) in rod and cone photoreceptors. J. Biol. Chem. 282:8837-8847
3. Zhang H, et al. (2004) Photoreceptor cGMP Phosphodiesterase ‰-Subunit (PDE‰) Functions as a Prenyl Binding Protein. J. Biol. Chem. 279:407-13
4. Avasthi P, Watt CB, Williams DS, Le YZ, Li S, Chen CK, Frederick JM, Baehr W (2009) Heterotrimeric kinesin-2 is required for trafficking of membrane proteins to cone, but not rod, outer segments. Submitted
5. Zhang H, Fan J, Li S, Karan S, Rohrer B, Palczewski K, Frederick JM, Crouch RK, Baehr W (2008) Trafficking of Membrane-associated Proteins to Cone Photoreceptor Outer Segments Requires 11-cis-Retinal. J Neurosci 2(15)4008-4015
6. Karan S, Zhang H, Li S, Frederick JM, Baehr W (2008) A model for transport of membrane-associated phototransduction polypeptides in rod and cone photoreceptor inner segments. Vision Res 48:442-452
