A Challenge of Numbers and Diversity: Neurogenesis in theDrosophilaOptic Lobe

Abstract

The brain areas that endow insects with the ability to see consist of remarkably complex neural circuits. Reiterated arrays of many diverse neuron subtypes are assembled into modular yet coherent functional retinotopic maps. Tremendous progress in developing genetic tools and cellular markers over the past years advanced our understanding of the mechanisms that control the stepwise production and differentiation of neurons in the visual system of Drosophila melanogaster. The postembryonic optic lobe utilizes at least two modes of neurogenesis that are distinct from other parts of the fly central nervous system. In the first optic ganglion, the lamina, neuroepithelial cells give rise to precursor cells, whose proliferation and differentiation depend on anterograde signals from photoreceptor axons. In the second optic ganglion, the medulla, the coordinated activity of four signaling pathways orchestrates the gradual conversion of neuroepithelial cells into neuroblasts, while a specific cascade of temporal identity transcription factors controls subtype diversification of their progeny.

Minibrain drives the Dacapo dependent cell cycle exit of neurons in the Drosophila brain by promoting asense and prospero expression

“…The OPC is located laterally on the OL surface and it gives rise to the lamina precursor cells (LPCs) and medulla neurons, whereas the IPC, which is located inside the lobe, generates the lobula neurons (Hofbauer and Campos-Ortega, 1990; reviewed by Meinertzhagen and Hanson, 1993;Apitz and Salecker, 2014). The adult CB originates from ∼100 NBs located medially in each hemisphere.…”

From the Eye to the Brain

“…2 Bf). They are converted into neuroblasts in a moving proneural wave (reviewed in (Apitz and Salecker 2014)). These medulla neuroblasts divide asymmetrically to self-renew and generate their progeny composed of neurons and glia (Egger et al 2007).…”

“…Lamina neurons are produced and differentiate in response to Hedgehog (Hh) and EGF produced by photoreceptors axons (Selleck et al 1992, Huang and Kunes 1996, Huang and Kunes 1998, Huang et al 1998). By 25 hrs APF, it has generated about 6,000 additional cells that become lamina neurons and glia (Apitz and Salecker 2014). The development of the OPC, which generates the lamina and the medulla, has been studied in much detail while the development of the IPC, which generates the lobula and lobula plate, has only recently been the topic of investigations (Apitz and Salecker 2015, Neriec et al Submitted).…”

“…The AS-C protein L(1)sc is expressed in the transition zone between neuroepithelium and neuroblasts and, along with Notch, is necessary for the proneural wave (Egger et al 2007, Yasugi et al 2008, Apitz and Salecker 2014). In the IPC, cells undergo EMT and delaminate to later become neuroblasts after migration to the dIPC, most likely also under the control of L(1)sc and Notch (Apitz and Salecker 2015, Neriec et al Submitted).…”

“…These factors are often transmitted to the post-mitotic neurons, affecting the adult identity of the neuronal progeny (Isshiki et al 2001, Bayraktar et al 2010, Li et al 2013b, Bertet et al 2014). Despite differences in the transcription factor repertoire used in these temporal series, the general mechanism is very similar: one transcription factor induces expression of the next but also represses expression of the previous; changes in transcription factor expression are correlated with changes in adult neuronal progeny (Li et al 2013a, Apitz and Salecker 2014). Studies in vertebrates seem to indicate that similar temporal series also play an important role in mammalian neurogenesis, including the mouse retina (Livesey and Cepko 2001, Wang et al 2014a, Mattar et al 2015).…”