Generation and Evolution of Neural Cell Types and Circuits: Insights from the Drosophila Visual System

Abstract

The Drosophila visual system has become a premier model for probing how neural diversity is generated during development. Recent work has provided deeper insight into the elaborate mechanisms that control the range of types and numbers of neurons produced, which neurons survive, and how they interact. These processes drive visual function and influence behavioral preferences. Other studies are beginning to provide insight into how neuronal diversity evolved in insects by adding new cell types and modifying neural circuits. Some of the most powerful comparisons have been those made to the Drosophila visual system, where a deeper understanding of molecular mechanisms allows for the generation of hypotheses about the evolution of neural anatomy and function. The evolution of new neural types contributes additional complexity to the brain and poses intriguing questions about how new neurons interact with existing circuitry. We explore how such individual changes between species might play a role over evolutionary timescales. Lessons learned from they visual system apply to other neural systems, including they central brain, where decisions are made and memories are stored.

Establishment and maintenance of motor neuron identity via temporal modularity in terminal selector function

“…Nervous system development is a multi-step process that culminates in the generation of distinct neuron types necessary for animal behavior. Seminal studies in many model systems have begun to elucidate the molecular mechanisms that control the early steps of neuronal development, such as specification of neural progenitors and generation of post-mitotic neurons ( Catela and Kratsios, 2019 ; Doe, 2017 ; Greig et al, 2013 ; Jessell, 2000 ; Lodato and Arlotta, 2015 ; Perry et al, 2017 ). However, our understanding of the final steps of neuronal development is very rudimentary.…”

Muscarinic acetylcholine receptor signaling generates OFF selectivity in a simple visual circuit

“…N and OFF selectivity, the differential neuronal responses elicited by signal increments or decrements, is an essential component of visual computation and a fundamental property of visual systems across species [1][2][3] . Extensive studies of adult Drosophila optic ganglia and vertebrate retinae suggest that the construction principles of ON and OFF selective pathways are shared among visual systems, albeit with circuit-specific implementations [4][5][6] . Anatomically, dedicated neuronal pathways for ON vs. OFF responses are key features in visual circuit construction.…”

Cell segregation and boundary formation during nervous system development

“…It is composed of four ganglia lamina, medulla, lobula, and lobula plate. The optic lobes process all the visual information, and then convey this information to the optic glomeruli in the central brain (Apitz and Salecker, 2014, Contreras et al, 2019, Ngo et al, 2017, Perry et al, 2017. The development of this structure begins with the formation of the optic placode, which originates from a group of 30-40 cells located in the posterior region of the procephalic region, around stage 11 of embryonic development (Contreras et al, 2019, Hartenstein andCampos-Ortega, 1984).…”