Fig. 4.

ret expression in sympathetic ganglia (SYG) and dorsal root ganglia (DRG) during mouse embryogenesis. ret is detected in SYG and DRG during embryonic day 11. Whereas expression in DRG is initally restricted to few neurons of large diameter, expression in SYG is found at this stage throughout the ganglion. During the third week of embryonic development, an increasing number of small neurons in DRG initiates ret expression, while expression in sympathetic ganglia is restricted to a subset of neurons thus distinguishing a “progressive increase” from a “progressive restriction” of gene expression to neuron subpopulations (arrow NGF requirement for the increase in the ret-positive population in DRG)