Asymmetric Cell Division of Drosophila Neuroblasts
In Drosophila melanogaster, asymmetric cell division plays an important role in neural development. Neuroblasts are the progenitor cells which divide asymmetrically to give rise to another neuroblast and a ganglion mother cell (GMC). The neuroblast repeatedly undergoes this asymmetric cell division while the GMC continues on to produce a pair of neurons. Two proteins play an important role in setting up this asymmetry in the neuroblast, Prospero and Numb. These proteins are both synthesized in the neuroblast and segregate into only the GMC during divisions. Numb is a suppressor of Notch, therefore the asymmetric segregation of Numb to the basal cortex biases the response of the daughter cells to Notch signaling, resulting in two distinct cell fates. Prospero is required for gene regulation in GMCs. It is equally distributed throughout the neuroblast cytoplasm, but becomes localized at the basal cortex when the neuroblast starts to undergo mitosis. Once the GMC buds off from the basal cortex, Prospero becomes translocated into the GMC nucleus to act as a transcription factor.
Other proteins present in the neuroblast mediate the asymmetric localization of Numb and Prospero. Miranda is an anchoring protein that binds to Prospero and keeps it in the basal cortex. Following the generation of the GMC, Miranda releases Prospero and then becomes degraded. The segregation of Numb is mediated by Pon (the partner of Numb protein). Pon binds to Numb and colocalizes with it during neuroblast cell division.
The mitotic spindle must also align parallel to the asymmetrically distributed cell fate determinants to allow them to become segregated into one daughter cell and not the other. The mitotic spindle orientation is mediated by Inscuteable, which is segregated to the apical cortex of the neuroblast. Without the presence of Inscuteable, the positioning of the mitotic spindle and the cell fate determinants in relationship to each other becomes randomized. Inscuteable mutants display a uniform distribution of Miranda and Numb at the cortex, and the resulting daughter cells display identical neuronal fates.
Read more about this topic: Asymmetric Cell Division
Famous quotes containing the words cell and/or division:
“Women have no wilderness in them,
They are provident instead,
Content in the tight hot cell of their hearts
To eat dusty bread.”
—Louise Bogan (1897–1970)
“If the technology cannot shoulder the entire burden of strategic change, it nevertheless can set into motion a series of dynamics that present an important challenge to imperative control and the industrial division of labor. The more blurred the distinction between what workers know and what managers know, the more fragile and pointless any traditional relationships of domination and subordination between them will become.”
—Shoshana Zuboff (b. 1951)