Editing Neuroblast (section)

== Neuroblast development in ''Drosophila'' ==
In the fruit fly [[model organism]] ''[[Drosophila melanogaster]],'' a neuroblast is a neural progenitor cell which divides asymmetrically to produce a neuroblast and either a neuron, a [[ganglion mother cell]] (GMC), or an intermediate neural progenitor, depending on the type of neuroblast.<ref name="Gaillaud">{{cite book |last1=Gallaud |first1=E |last2=Pham |first2=T |last3=Cabernard |first3=C |title=Asymmetric Cell Division in Development, Differentiation and Cancer |chapter=Drosophila melanogaster Neuroblasts: A Model for Asymmetric Stem Cell Divisions |series=Results and Problems in Cell Differentiation |date=2017 |volume=61 |pages=183–210 |doi=10.1007/978-3-319-53150-2_8 |pmid=28409305|isbn=978-3-319-53149-6 }}</ref><ref name=":0">{{Cite journal|last=Doe|first=Chris Q.|date=2017-10-06|title=Temporal Patterning in the Drosophila CNS|journal=Annual Review of Cell and Developmental Biology|language=en|volume=33|issue=1|pages=219–240|doi=10.1146/annurev-cellbio-111315-125210|pmid=28992439|issn=1081-0706|doi-access=free}}</ref> During [[Embryonic development|embryogenesis]], embryonic neuroblasts delaminate from either the procephalic neuroectoderm (for brain neuroblasts), or the [[ventral nerve cord]] neuroectoderm (for abdominal neuroblasts). During larval development, [[Optic lobe (arthropods)|optic lobe]] neuroblasts are generated from a neuroectoderm called the Outer Proliferation Center.<ref>{{Cite journal|last1=Courgeon|first1=Maximilien|last2=Desplan|first2=Claude|date=2019-06-01|title=Coordination of neural patterning in the Drosophila visual system|url= |journal=Current Opinion in Neurobiology|series=Neuronal Identity|language=en|volume=56|pages=153–159|doi=10.1016/j.conb.2019.01.024|pmid=30849690|issn=0959-4388|pmc=6551251}}</ref> There are more than 800 optic lobe neuroblasts, 105 central brain neuroblasts, and 30 abdominal neuroblasts per hemisegment (a bilateral half of a segment).<ref name=":0" />

Neuroblasts undergo three known division types. Type 0 neuroblasts divide to give rise to a neuroblast, and a daughter cell which directly differentiates into a single neuron or glia. Type I neuroblasts give rise to a neuroblast and a [[ganglion mother cell]] (GMC), which undergoes a terminal division to generate a pair of sibling neurons. This is the most common form of cell division, and is observed in abdominal, optic lobe, and central brain neuroblasts. Type II neuroblasts give rise to a neuroblast and a transit amplifying Intermediate Neural Progenitor (INP).  INPs divide in a manner similar to type I neuroblasts, producing an INP and a ganglion mother cell.  While only 8 type II neuroblasts exist in the central brain, their lineages are both much larger and more complex than type I neuroblasts.<ref name=":0" /> The switch from pluripotent neuroblast to differentiated cell fate is facilitated by the proteins Prospero, [[NUMB (gene)|Numb]], and Miranda. Prospero is a transcription factor that triggers differentiation. It is expressed in neuroblasts, but is kept out of the nucleus by Miranda, which tethers it to the cell basal cortex. This also results in asymmetric division, where Prospero localizes in only one out of the two daughter cells. After division, Prospero enters the nucleus, and the cell it is present in becomes the GMC.

Neuroblasts are capable of giving rise to the vast neural diversity present in the fly brain using a combination of spatial and temporal restriction of gene expression that give progeny born from each neuroblast a unique identity depending both their parent neuroblast and their birth date.<ref>{{Cite journal|last1=Sen|first1=Sonia Q|last2=Chanchani|first2=Sachin|last3=Southall|first3=Tony D|last4=Doe|first4=Chris Q|date=2019-01-29|editor-last=Mandel|editor-first=Gail|editor2-last=Struhl|editor2-first=Kevin|editor3-last=Desplan|editor3-first=Claude|editor4-last=Eisen|editor4-first=Michael B|title=Neuroblast-specific open chromatin allows the temporal transcription factor, Hunchback, to bind neuroblast-specific loci|journal=eLife|volume=8|pages=e44036|doi=10.7554/eLife.44036|pmid=30694180|pmc=6377230|issn=2050-084X|doi-access=free}}</ref> This is partly based on the position of the neuroblast along the Anterior/Posterior and Dorsal/Ventral axes, and partly on a temporal sequence of transcription factors that are expressed in a specific order as neuroblasts undergo sequential divisions.<ref>{{cite journal |last1=Kohwi |first1=M |last2=Hiebert |first2=LS |last3=Doe |first3=CQ |title=The pipsqueak-domain proteins Distal antenna and Distal antenna-related restrict Hunchback neuroblast expression and early-born neuronal identity. |journal=Development |date=May 2011 |volume=138 |issue=9 |pages=1727–35 |doi=10.1242/dev.061499 |pmid=21429984 |pmc=3074449 }}</ref>