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. Author manuscript; available in PMC: 2012 Nov 21.
Published in final edited form as: Nat Rev Neurosci. 2003 Feb;4(2):113–120. doi: 10.1038/nrn1036

Figure 3. Events during new synapse formation at the Drosophila neuromuscular junction, and the role of Wnt and TGFβ pathway in these processes.

Figure 3

a, b | During Drosophila neuromuscular (NMJ) development, precise apposition of the pre- and postsynaptic molecular components is required for bouton maturation and subsequent expansion. New boutons bud out from existing mature boutons to adjust for an increase in target muscle size. c, d | New buds expand and subsequently mature in tune with a synchronous folding of the postsynaptic membrane into the subsynaptic reticulum (SSR). Recent observations at the Drosophila NMJ demonstrate crucial roles for the Wnt and transforming growth factor-β (TGFβ) signal transduction pathways in these processes20–22. e | In the absence of Wingless (Wg) function, fewer synapses form, and those that do form fail to develop pre- and postsynaptic densities, T-bars and postsynaptic SSR. The presynaptic cytoskeletal network appears to be destabilized, and postsynaptic glutamate receptors (GluR) are not correctly localized. f | wit mutant synapses have normal SSR and apparently normal GluR localization. However, they have presynaptic defects such as an increase in the number of T-bars per presynaptic density, abnormal apposition of pre- and postsynaptic densities, and an abnormal appearance of presynaptic T-bars. These studies indicate a presynaptic role for the TGFβ type II receptor, Wit, which functions as a part of a retrograde signalling mechanism to adjust the size of the presynaptic arborization to the postsynaptic muscle size. By contrast, Wg is secreted by presynaptic boutons, and seems to function in an anterograde fashion to control the correct positioning of active zones and postsynaptic SSR, as well as bouton number. Together, they coordinate synapse development by regulating bouton budding, cytoskeletal stability, number of functional active zones, folding of the postsynaptic muscle membrane, and levels of pre- and postsynaptic molecules, including GluRs and cell adhesion molecules. DFz2, Drosophila Frizzled 2; Spin, Spinster.