Developmental expression of dynamin in the chick retinotectal system

Dynamin 1, a GTPase involved in the endocytic cycle of synaptic vesicle mem branes, is believed to support axonal outgrowth and/or synaptogenesis. To e xplore the temporal and spatial patterns of dynamin 1 distribution in neuro nal morphogenesis, we compared the developmental expression of dynamin with the expression of presynaptic membrane proteins such as SV2, synaptotagmin , and syntaxin in the chick primary visual pathway. Western blots of retina and tectum revealed a steady increase of synaptotagmin and syntaxin from e mbryonic Day 7 (E7) to E11, whereas for the same time frame no detectable i ncrease of dynamin was found. Later stages showed increasing amounts of all tested proteins until the first postnatal week. Immunofluorescence reveale d that SV2, synaptotagmin, and syntaxin are present in retinal ganglion cel l axons from E4 on. In later stages, the staining pattern in the retina and along the visual pathway paralleled the formation and maturation of axons. In contrast, dynamin is not detectable by immunofluorescence in the develo ping retina and optic tectum before synapse formation. Our data indicate th at, in contrast to the early expression of synaptotagmin, SV2, and syntaxin during axonal growth, dynamin is upregulated after synapse formation, sugg esting its function predominantly during and after synaptogenesis but not i n axonogenesis.