Characterization of a Novel Growth Promoting Invertebrate Gene in Central Neurons

Axotomized central neurons of most invertebrate species demonstrate a strong regenerative capacity, and as such may provide valuable molecular insights and new tools to promote neurite growth in mammalian neurons. This thesis characterizes a novel molluscan protein, caltubin, ubiquitously expressed in central neurons of Lymnaea stagnalis and locally synthesized in regenerating neurites. Reduction of caltubin levels by gene silencing inhibits outgrowth and regenerative ability of adult Lymnaea neurons and decreases local tubulin levels in neurites. Expression of caltubin in PC-12 cells and mouse cortical neurons promotes nerve growth factor-induced axonal outgrowth and attenuates axonal retraction after injury. Caltubin binds to tubulin in both Lymnaea and mammalian neurons. In Lymnaea neurons, knockdown of caltubin modulated the calcium dynamics and reduced the whole-cell current conductance of voltage-gated calcium channels (VGCCs) in the soma and growth cones. Co-expression of caltubin in tsA201 cells increased the calcium conductance of CaV2.1 channels, likely by increasing surface expression of the channels. This is the first study illustrating that a xenoprotein can enhance outgrowth and prevent degeneration of injured mammalian neurons through a conserved interaction with tubulin. These results may open up new avenues in molecular repair strategies through the insertion of molecular components of invertebrate regenerative pathways into mammalian neurons.Ph