page_title: Ganglion mother cell
section_title: Mitotic division of Neuroblasts in Drosophila
hierarchical_section_title: Ganglion mother cell / Mitotic division of Neuroblasts in Drosophila
caption_attribution_description: English: Asymmetric cell division in Drosophila neuroblasts. Apical (red) and basal (blue) proteins are asymmetrically segregated at cortical ends of the neuroblast at the time of mitosis. Members of the apical complex are involved in the asymmetric partitioning of basal determinants, in establishing cell polarity and in the correct orientation of the mitotic spindle. The apical complex consisting of aPKC, Par3, and Par6 is linked to the Gαi-PINS-MUD complex via Inscuteable. The basal complex consists of the cell-fate determinants, Miranda, Prospero, Brat, and Numb.
context_page_description: Ganglion mother cells are cells involved in neurogenesis, in non-mammals, that divide only once to give rise to two neurons, or one neuron and one glial cell or two glial cells, and are present only in the central nervous system. They are also responsible for transcription factor expression. While each ganglion mother cell necessarily gives rise to two neurons, a neuroblast can asymmetrically divide multiple times. GMCs are the progeny of type I neuroblasts. Neuroblasts asymmetrically divide during embryogenesis to create GMCs. GMCs are only present in certain species and only during the embryonic and larval stages of life. Recent research has shown that there is an intermediate stage between a GMC and two neurons. The GMC forms two ganglion cells which then develop into neurons or glial cells. Embryonic neurogenesis has been extensively studied in Drosophila melanogaster embryos and larvae.
context_section_description: The daughter cells of a neuroblast have two decidedly different neural fates. This is accomplished by neural fate determinants, important proteins that segregate asymmetrically. Most notable are Numb and Prospero. These proteins are evenly distributed in the neuroblast until mitosis occurs and they segregate totally into the newly formed GMC  During Mitosis Numb and Prospero localize to the basal cortex from which the GMC buds off. 
  Numb is a suppressor of a signal protein called Notch. Suppressing Notch signaling allows the daughter cells to react to the same signal in different ways, allowing them to have different neural fates.
  Prospero is responsible for gene regulation in the GMC.
  Both of these proteins co-function with adapter proteins that facilitate their transition to the basal cortex during Mitosis. These proteins are Miranda and Pon.
  Miranda localizes basally during interphase and then binds to Prospero, anchoring it to the basal cortex. Once the GMC has been created, Miranda releases Prospero, which evenly distributes throughout the new cell, and Miranda degrades.
  Pon also known as "partner of Numb" binds to Numb and co-localizes with it during Mitosis.
  These four proteins act to inhibit self-renewal (the cell cycle) and promote differentiation (especially Prospero), which is why GMCs divide into their differentiated progeny instead of more GMCs. Cell cycle progression is inhibited by Prospero because it activates cyclin-dependent kinase inhibitor (CKI).
  The vital differentiating proteins that are segregated into the daughter neuroblast and not the GMC are Bazooka, aPKC, Inscutable, and Partner of Inscutable (Pins). The proteins (with the exception of aPKC) form a ternary complex at the apical cortex independent of the proteins that segregate towards the basal cortex. The protein aPKC promotes self-renewal, encouraging the neuroblast to keep dividing and carry out its lineage.
  Research has suggested that certain tumor-suppressing proteins (Lgl, Dlg, or Brat) play a critical role in the asymmetric segregation of neural fate determinants and their localization to the basal cortex . In clonal lines of neuroblasts that had been manipulated so that they lacked Lgl activity, Miranda did not segregate asymmetrically, but was evenly distributed throughout the cortex.
  The temporal regulation of neuroblast asymmetric division is controlled by proteins Hunchback (Hb) and sevenup (svp). After division svp accumulates in both daughter cells and down-regulates Hb. In the GMC Prospero down-regulates svp, inhibiting the temporal trigger of cellular division.
caption: Segregation of transcription factors during asymmetric division of a type I neuroblast
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