UCLA

This work examines a variety of fundamental biological questions regarding the

central brain of D. melanogaster. These questions focus on topics relating to neurons

which form the neural circuits of the larval and adult brain. We focused specifically on

the neurons which form the central brain and are organized into developmental-structural units termed lineages. Through a combination of genetics and

immunohistochemical assays we were able to create a detailed atlas of lineages in the

early larval brain (made by embryonic-born primary neurons) and the adult brain (made

mostly by larval-born secondary neurons; Chapters 2 and 6); show that secondary

lineages are born in a strict temporal manner and how they develop during larval and

pupal stages (Chapters 3-5). By observing secondary lineages in both wild-type and

various mutant conditions we were able to show the following: pattern and timing of

secondary lineage axon tract extension in the larva; movement of cell body clusters due

to the growing central brain and optic lobe neuropils during metamorphosis; which

secondary lineages retain their entire cohort of neurons (many lose a hemilineage in the

pupa); and proper differentiation of secondary lineages relies on the presence of both

synaptic partners. Taken together, these studies make a significant contribution to our

understanding of Drosophila brain circuitry and development. They support the overall

goal of mapping all central brain lineages (primary and secondary components), from

their inception in the early embryo (when neuroblasts first appear) to their final mature

form in the adult.