Kathryn V. Anderson: Dorsal-Ventral Patterning in the Spinal Cord

Sonic hedgehog (Shh) signaling is required for specification of six different cell types in the ventral neural tube. The core of the Hedgehog signaling pathway is evolutionarily conserved, but we have identified more than six genes that are required for Hedgeghog signaling in the mouse but not in Drosophila.

At least five of these novel Shh pathway genes affect the primary cilium. Primary cilia are microtubule-based organelles that extend from the surface of most non-dividing vertebrate cells (Fig. 1).

Cilia in the mouse node Figure 1. Cilia in the mouse node. In the wild-type node, long microtubule-based cilia are present, in addition to the much shorter actin-based microvilli. A specific dynein is required to transport material from the tip of the cilium back to the base; mutants that lack that dynein (Dnchc2lln) have bulges along the length of the cilium.

For example, a dynein heavy chain gene is required for retrograde transport. We identified four different mutations in the gene that encodes the heavy chain of the dynein motor required for retrograde transport in the cilium. These mutants have two phenotypes: abnormally shaped cilia and loss of ventral cell types in the neural tube (Fig.2)

Ventral neural cell types, marked by expression of Shh and Nkx2.2 Figure 2. Ventral neural cell types, marked by expression of Shh and Nkx2.2, fail to be specified in mutants that lack the heavy chain dynein retrograde IFT motor of cilia (Dnchc2lln).

Our studies have led to the conclusion that cilia are required for the ability of mammalian cells to respond to Hedgehog ligands, and that organized trafficking within the cilium is essential for Hedgehog signal transduction.

The lab is currently pursuing studies to define the events that occur within cilia and to test whether other developmental signaling pathways depend on cilia. We also continue to identify and characterize other new mutations that affect neural patterning.

Huangfu, D., Liu, A., Rakeman, A.S., Murcia, M.S., Niswander, L., Anderson, K.V. (2003) Hedgehog signalling in the mouse requires intraflagellar transport proteins. Nature. 426: 83-87

Garcia-Garcia, M. J., Eggenschwiler, J. T., Caspary, T., Alcorn, H. L., Wyler, M. R., Huangfu, D., Rakeman, A. S., Lee, J. D., Feinberg, E. H, Timmer, J. R. and Anderson, K. V. (2005) Analysis of mouse embryonic patterning and morphogenesis by forward genetics. Proc. Natl. Acad. Sci. USA. 102: 5913-5919.

Huangfu, D. and Anderson, K. V. (2005) Cilia and Hedgehog responsiveness in the mouse. Proc. Natl. Acad. Sci. USA 102: 11325-11330.

Eggenschwiler, J.T., Bulgakov, O.V., Qin, J., Li, T., Anderson, K.V. (2006) Mouse Rab23 regulates Hedgehog signaling from Smoothened to Gli proteins. Dev Biol. 290(1):1-12.

Huangfu, D., Anderson, K.V. (2006) Signaling from Smo to Ci/Gli: conservation and divergence of Hedgehog pathways from Drosophila to vertebrates. Development. 133(1):3-14.

Weatherbee, S. D., Anderson, K. V. and Niswander, L. A. (2006) LDL-receptor-related protein 4 is critical for formation of the neuromuscular junction. Development 133: 4993-5000.

Caspary T, Larkins CE, Anderson KV. (2007) The graded response to sonic hedgehog depends on cilia architecture. Dev Cell. 12(5):767-78.

Ocbina, P. J. R. and Anderson, K. V. (2008) Intraflagellar Transport, Cilia and Mammalian Hedgehog Signaling: Analysis in Mouse Embryonic Fibroblasts. Dev. Dyn. 237: 2030-2038.

Liem, K. F. Jr, He. M., Ocbina, P. J. and Anderson, K. V. (2009) Mouse Kif7/Costal2 is a cilia-associated protein that regulates Sonic hedgehog signaling. Proc Natl Acad Sci USA. 106: 13377-13382.

Ocbina, P. J., Tuson, M. and Anderson, K. V. (2009) Primary Cilia Are Not Required for Normal Canonical Wnt Signaling in the Mouse Embryo. PLoS One. e6839

Weatherbee, S. D., Niswander, L. A. and Anderson, K. V. (2009) A mouse model for Meckel syndrome reveals Mks1 is required for ciliogenesis and Hedgehog signaling. Hum. Mol. Genet. 18: 4565-4575.

Goetz, S. C., Anderson, K. V. (2010). The primary cilium: a signalling centre during vertebrate development. Nat Rev Genet.11: 331-344.