GM2 ganglioside as a regulator of pyramidal neuron dendritogenesis

One of the most profound events in the life of a neuron in the mammalian CNS is the development of a characteristic dendritic tree, yet little is understood about events controlling this process. Pyramidal neurons of the cerebral cortex are known to undergo a single explosive burst of dendritic sprouting immediately after completing migration to the cortical mantle, and following maturation there is no evidence that new, primary dendrites are initiated. Yet in one group of rare genetic diseases--Tay-Sachs disease and related neuronal storage disorders--cortical pyramidal neurons undergo a second period of dendritogenesis. New dendritic membrane is generated principally at the axon hillock and in time is covered with normal-appearing spines and synapses. In our studies of normal brain development and storage diseases we consistently find one feature in common in cortical pyramidal neurons undergoing active dendritogenesis: They exhibit dramatically increased expression of GM2 ganglioside localized to cytoplasmic vacuoles within neuronal perikarya and proximal dendrites. There is also evidence that the increase in GM2 precedes dendritic spouting, and that after dendritic maturation is complete (in normal brain) the GM2 levels in neurons become substantially reduced. These findings are consistent with GM2 ganglioside playing a pivotal role in the regulation of dendritogenesis in cortical pyramidal neurons.