Summary of the Mushroom Body Development

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Figure 8 - Summary of the mushroom body development.

One MB is derived from 4 identical Nbs in each hemisphere. By asymmetric divisions through the embryonic, larval, and pupal stages, each MB Nb generates about 500 neurons (Technau and Heisenberg, 1982), which can be classified into 3 types based on their axonal projection patterns. These 3 types of MB neurons are born in a specific temporal order. g neurons (red) are born before the mid-3rd instar stage, a'/b' neurons (green) are born between the mid-3rd instar stage and PF, and a/b neurons (blue) are born after PF. In the larval life, all MB neurons, including g and a'/b' neurons, acquire similar morphologies, although both dendritic elaboration and axonal side branching look relatively immature in a'/b' neurons. During the early pupal stage, g neurons change their axonal projection pattern after partial degeneration of their axons. In addition, degeneration of larval dendrites followed by elaboration of adult dendrites occurs in pupae. The axons from different types of neurons are fasciculated into separate bundles. In the lobe region, the axonal bundles from g neurons, a'/b' neurons, and a/b neurons correspond to the g lobe, the a'/b' lobes, and the a/b lobes, respectively.


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