Mammalian Numb (mNumb) has multiple functions and plays important roles in the regulation of neural development, including maintenance of neural progenitor cells and promotion of neuronal differentiation in the central nervous system (CNS). However, the molecular bases underlying the distinct functions of Numb have not yet been elucidated. mNumb, which has four splicing isoforms, can be divided into two types based on the presence or absence of an amino acid insert in the proline-rich region (PRR) in the C-terminus. It has been proposed that the distinct functions of mNumb may be attributable to these two different types of isoforms. In this study, we used the outer optic anlage (OOA) of the Drosophila larval brain as an assay system to analyze the functions of these two types of isoforms in the neural stem cells, since the proliferation pattern of neuroepithelial (NE) stem cells in the OOA closely resembles that of the vertebrate neural stem/progenitor cells. They divide to expand the progenitor cell pool during early neurogenesis and to produce neural precursors/neurons during late neurogenesis. Clonal analysis in the OOA allows one to discriminate between the NE stem cells, which divide symmetrically to expand the progenitor pool, and the postembryonic neuroblasts (pNBs), which divide asymmetrically to produce neural precursors (ganglion mother cells), each of which divides once to produce two neurons. We found that in the OOA, the human Numb isoform with a long PRR domain (hNumb-PRRL), which is mainly expressed during early neurogenesis in the mouse CNS, promotes proliferation of both NE cells and pNBs without affecting neuronal differentiation, while the other type of hNumb isoform with a short PRR domain (hNumb-PRRS), which is expressed throughout neurogenesis in the mouse embryonic CNS, inhibits proliferation of the stem cells and promotes neuronal differentiation. We also found that hNumb-PRRS, a functional homologue of Drosophila Numb, more strongly decreases the amount of nuclear Notch than hNumb-PRRL, and could antagonize Notch functions probably through endocytic degradation, suggesting that the two distinct types of hNumb isoforms could contribute to different phases of neurogenesis in the mouse embryonic CNS.
"At late second instar, the NEs on the medial edge of the OPC begin to differentiate into medulla neuroblasts (NBs). These neuroblasts undergo asymmetric division producing a neuroblast daughter and a smaller ganglion mother cell (GMC) that divides once to generate two medulla neurons (Figure 1B) –. This proliferation and differentiation pattern closely resembles that of neural progenitor cells in the developing vertebrate brain –. "
[Show abstract][Hide abstract] ABSTRACT: As one of the major hydrolases in Drosophila, trehalase (Treh) catalyzes the hydrolysis of trehalose into glucose providing energy for flight muscle activity. Treh is highly conserved from bacteria to humans, but little is known about its function during animal development. Here, we analyze the function of Treh in Drosophila optic lobe development. In the optic lobe, neuroepithelial cells (NEs) first divide symmetrically to expand the stem cell pool and then differentiate into neuroblasts, which divide asymmetrically to generate medulla neurons. We find that the knockdown of Treh leads to a loss of the lamina and a smaller medulla. Analyses of Treh RNAi-expressing clones and loss-of-function mutants indicate that the lamina and medulla phenotypes result from neuroepithelial disintegration and premature differentiation into medulla neuroblasts. Although the principal role of Treh is to generate glucose, the Treh loss-of-function phenotype cannot be rescued by exogenous glucose. Thus, our results indicate that in addition to being a hydrolase, Treh plays a role in neuroepithelial stem cell maintenance and differentiation during Drosophila optic lobe development.
PLoS ONE 07/2014; 9(7):e101433. DOI:10.1371/journal.pone.0101433 · 3.23 Impact Factor
"Numb PRRL isoforms promote proliferation of a variety of progenitor cells including neuroepithelial stem cells of the Drosophila larval brain, P19 embryonic carcinoma cells as well as primary and immortalized neural crest stem cell lines [19,50,56]. In contrast, PRRS isoforms inhibit proliferation and promote neuronal differentiation of these same cells [19,50,56]. The presence or absence of the PTB insert did not significantly contribute to the ability of the Numb isoforms to influence the proliferation and differentiation of the progenitor cells . "
[Show abstract][Hide abstract] ABSTRACT: Members of the vertebrate Numb family of cell fate determinants serve multiple functions throughout early embryogenesis, including an essential role in the development of the nervous system. The Numb proteins interact with various partner proteins and correspondingly participate in multiple cellular activities, including inhibition of the Notch pathway.
Here, we describe the expression characteristics of Numb and Numblike (NumbL) during Xenopus development and characterize the function of NumbL during primary neurogenesis. NumbL, in contrast to Numb, is expressed in the territories of primary neurogenesis and is positively regulated by the Neurogenin family of proneural transcription factors. Knockdown of NumbL afforded a complete loss of primary neurons and did not lead to an increase in Notch signaling in the open neural plate. Furthermore, we provide evidence that interaction of NumbL with the AP-2 complex is required for NumbL function during primary neurogenesis.
We demonstrate an essential role of NumbL during Xenopus primary neurogenesis and provide evidence for a Notch-independent function of NumbL in this context.
"As the proneural wave progresses, the number of neuronal progeny of each NB increases. However, medulla NBs may disappear at some point due to differentiation or apoptosis (Egger et al., 2007; Hofbauer and Campos-Ortega, 1990; Toriya et al., 2006). There are several reasons for thinking that the secondary axis of differentiation may be related to the formation of columnar units of the medulla (Hasegawa et al., 2011). "
[Show abstract][Hide abstract] ABSTRACT: Sequential progression of differentiation in a tissue or in multiple tissues in a synchronized manner plays important roles in development. Such waves of differentiation are especially important in the development of the Drosophila visual system, which is composed of the retina and the optic lobe of the brain. All of the components of the fly visual system are topographically connected, and each ommatidial unit in the retina corresponds to a columnar unit in the optic lobe, which is composed of lamina, medulla, lobula and lobula plate. In the developing retina, the wave of differentiation follows the morphogenetic furrow, which progresses in a posterior-to-anterior direction. At the same time, differentiation of the lamina progresses in the same direction, behind the lamina furrow. This is not just a coincidence: differentiated photoreceptor neurons in the retina sequentially send axons to the developing lamina and trigger differentiation of lamina neurons to ensure the progression of the lamina furrow just like the furrow in the retina. Similarly, development of the medulla accompanies a wave of differentiation called the proneural wave. Thus, the waves of differentiation play important roles in establishing topographic connections throughout the fly visual system. In this article, we review how neuronal differentiation and connectivity are orchestrated in the fly visual system by multiple waves of differentiation.
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