Professor of Ophthalmology & Visual Sciences and
Adjunct Professor 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
Molecular Biology Program
Rod and cone photoreceptors have 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. The outer segment is essentially a much enlarged primary cilium containing rhodopsin and the phototransduction cascade. 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. Integral membrane proteins are synthesized at 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-II, cytoplasmic dynein), small GTP binding proteins (rab28, rab9, ARL3, ARL13b), prenyl binding proteins mediating transport of prenylated proteins (PDE6D), acyl binding proteins (UNC119) involved in transport of G protein subunits. We are also focusing on genes involved in photoreceptor ciliogenesis and transition zone formation (NPHP5, NPHP10, INPP5E, centrins. CFAP36). We produce knockouts/knockins and transgenics to monitor the consequences of the mutation. Most frequently applied techniques are standard biochemistry/molecular biology, confocal and electron microscopy, electroretinography (photoreceptor function), optomotry (behavior), in-vivo electroporation (transfer of genes into neonatal retina), and gene therapy (AAV virus).
Trafficking of lipidated proteins (PDE6, GRK1, GNAT1) in Photoreceptor (Zhang et al., 2015). Lipidated proteins are extracted from the ER, and delivered by a lipid-binding protein (Λ). A key event is interaction with the Cargo Dislocation Factor ARL3-GTP which delivers cargo to the destination membrane Zhang et al., 2015).
- Zhang H, Constantine R, et al. (2011) UNC119 regulates G protein trafficking in sensory neurons. Nat Neurosci14, 874-880..
- Zhang T, Zhang N, et al. Y (2011). Cone opsin determines the time course of cone photoreceptor degeneration in Leber congenital amaurosis. Proc Natl Acad Sci USA 108, 8879-84.
- Zhang Z, He F, et al. (2015). Domain organization and conformational plasticity of the G protein effector, PDE6. J Biol Chem, 290(20):12833-43;
- Jiang L, Zhang H et al. (2011). Long-term RNA interference gene therapy in a dominant retinitis pigmentosa mouse model. Proc Natl Acad Sci USA 108, 18476-81.
- Constantine R, Zhang H et al. (2012). Uncoordinated(UNC)119: Coordinating the trafficking of myristoylated proteins. Vision Res 75, 26-32.
- Ying G, Avasthi P et al. (2014). Centrin 2 is required for mouse olfactory ciliary trafficking and development of ependymal cilia planar polarity. J Neurosci 34, 6377–6388.
- Zhang H, Li Jiang L et al. (2014). Mistrafficking of Prenylated Proteins Causes Retinitis Pigmentosa 2. FASEB J, 29(3):932-42..
- Jiang L, Wei Y et al. (2015). Heterotrimeric Kinesin-2 (KIF3) mediates transition zone and axoneme formation of mouse photoreceptors. J Biol Chem, 15;290(20):12765-78.
- Hanke-Gogokhia C, Wu Z, et al. (2016). Arf-like Protein 3 (ARL3) Regulates Protein Trafficking and Ciliogenesis in Mouse Photoreceptors. J Biol Chem, 291, 7142-7155.
- Ying G, Gerstner CD, et al. (2016). Small GTPases Rab8, Rab10 and Rab11 are Dispensable for Rhodopsin Trafficking in Mouse Photoreceptors. Published 16 Aug 2016 PLOS ONEhttp://dx.doi.org/10.1371/journal.pone.0161236.
- Ronquillo CC, Hanke-Gogokhia C, et al. (2016). Ciliopathy-associated IQCB1/NPHP5 protein is required for mouse photoreceptor outer segment formation. FASEB J. 30(10):3400-3412.
- Hanke-Gogokhia C, Yazigi H, et al. (2017) Arf-like Protein 13b (ARL13b), the ARL3 GEF, regulates assembly of the mouse photoreceptor transition zone. Submitted.