Formation and specification of a Drosophila dopaminergic precursor cell

Abstract

Dopaminergic neurons play important roles in animal behavior, including motivation, reward and locomotion. The Drosophila dopaminergic H-cell interneuron is an attractive system for studying the genetics of neural development because analysis is focused on a single neuronal cell type. Here we provide a mechanistic understanding of how MP3, the precursor to the H-cell, forms and acquires its identity. We show that the gooseberry/gooseberry-neuro (gsb/gsb-n) transcription factor genes act to specify MP3 cell fate. It is proposed that single-minded commits neuroectodermal cells to a midline fate, followed by a series of signaling events that result in the formation of a single gsb+/gsb-n+ MP3 cell per segment. The wingless signaling pathway establishes a midline anterior domain by activating expression of the forkhead transcription factors sloppy paired 1 and sloppy paired 2. This is followed by hedgehog signaling that activates gsb/gsb-n expression in a subgroup of anterior cells. Finally, Notch signaling results in the selection of a single MP3, with the remaining cells becoming midline glia. In MP3, gsb/gsb-n direct H-cell development, in large part by activating expression of the lethal of scute and tailup H-cell regulatory genes. Thus, a series of signaling and transcriptional events result in the specification of a unique dopaminergic precursor cell. Additional genetic experiments indicate that the molecular mechanisms that govern MP3/H-cell development might also direct the development of non-midline dopaminergic neurons.

Enhancer diversity and the control of a simple pattern of Drosophila CNS midline cell expression

“…Midline cell expression of a gene is particularly easy to identify due to the characteristic midline stripe of embryonic expression. The development of the midline cells is well understood, with many of the key regulatory proteins identified (Thomas et al, 1988; Watson et al, 2011; Watson and Crews, 2012; Wheeler et al, 2008). In particular, the Drosophila single-minded (sim) gene, which encodes a bHLH-PAS transcription factor, controls early development of the CNS midline cells (Nambu et al, 1991) by acting as a transcriptional activator that promotes the midline transcriptional program (Nambu et al, 1990) and indirectly represses the lateral CNS program (Estes et al, 2001).…”

“…Recent studies have promoted a model in which sim initially commits ectodermal cells to a single midline neuronal precursor fate followed by a series of signaling events that further diversify midline cell fates (Watson and Crews, 2012). During midline cell differentiation, sim continues to control transcription in midline glia (MG) (Estes et al, 2008; Wharton et al, 1994) and may interact with the Notch signaling pathway, another important regulator of MG transcription and development (Wheeler et al, 2008).…”

Chromatin profiling of Drosophila CNS subpopulations identifies active transcriptional enhancers

“…More detailed analysis of the FlyLight Gal4 lines revealed that all three fragments drive expression in distinct posterior midline subsets of the endogenous en/inv pattern (Fig. S1), which is likely to reflect the complexities of en/inv midline function (Watson et al, 2011;Watson and Crews, 2012;Wheeler et al, 2006). Subsequently, the publication of the Fly Enhancer database (Kvon et al, 2014) (Fig.…”

“…Drosophila CNS midline cells provide a useful experimental system for studying transcriptional regulation during CNS development. The development of the midline neurons and glia is well characterized with regards to both cellular and molecular mechanisms (Watson et al, 2011;Watson and Crews, 2012;Wheeler et al, 2008). Multiple large-scale screens have identified hundreds of genes that are expressed in midline cells (along with associated enhancers), and several transcription factors are known that control midline cell transcription (Kearney et al, 2004;Kvon et al, 2014;Manning et al, 2012;Tomancak et al, 2002Tomancak et al, , 2007Wheeler et al, 2006Wheeler et al, , 2009.…”

“…The initiation of midline cell development occurs during the mesectodermal stage (embryonic stages 5-8), mainly due to the activation of single-minded (sim) expression (Nambu et al, 1991). Formation of the midline primordium cells (stages 9-12) involves specification of neural precursors and midline glia by multiple signaling pathways (Watson et al, 2011;Watson and Crews, 2012;Wheeler et al, 2008), followed by division and development into neurons and glia. At the late embryonic midline stages (stages 13-17), the midline neurons complete terminal differentiation and the midline glia complete their apoptotic and migration steps to form the glial scaffold that supports the axon commissures.…”