The development of sensory ganglion cells in normal and Sprawling mutant mice.

The foetal and early post-natal development of dorsal root ganglion cells in normal and Sprawling (Swl) mutant mice was studied by light and electron microscopy. As early as the 11th foetal day the nucleus of some neurons showed an indentation of its membrane and by the 13th day this abnormality was marked and present in many ganglion cells of foetuses which were, therefore, identified as presumptive Swl'. A peripherally situated nucleus and the aggregation of filaments and organelles in the central perikaryon were also early abnormalities, similar to those of the sensory neurons of the adult Swl mouse. In the normal ganglion cells, nuclei were rounded and central by the 16th foetal day and nuclear indentations were never seen, thus making a clear distinction possible between normal and Swl foetuses.