Notch signaling acts before cell division to promote asymmetric cleavage and cell fate of neural precursor cells

Abstract

Asymmetric cell divisions in the central nervous system generate neurons of diverse fates. In Drosophila melanogaster, the protein Numb localizes asymmetrically to dividing neural precursor cells such that only one daughter cell inherits Numb. Numb inhibits Notch signaling in this daughter cell, resulting in a different cell fate from the Notch-induced fate in the other-Numb-negative-daughter cell. Precursor cells undergo asymmetric cytokinesis generating daughter cells of different sizes. I found that inactivation of Notch in fly embryonic neural precursor cells disrupted the asymmetric positioning of the cleavage furrow and produced daughter cells of the same size and fate. Moreover, inactivation of Notch at different times altered the degree of asymmetric Numb localization, such that earlier inactivation of Notch caused symmetric distribution of Numb and later inactivation produced incomplete asymmetric localization of Numb. The extent of asymmetrically localized Numb positively correlated with the degree of asymmetric cytokinesis and the size disparity in daughter cells. Loss of Numb or expression of constitutively active Notch led to premature specification of the precursor cells into the fate of one of the daughter cells. Thus, in addition to its role in the specification of daughter cell fate after division, Notch controls Numb localization in the precursor cells to determine the size and fate of daughter cells. Numb also inhibits Notch signaling in precursor cells to prevent Notch-induced differentiation of the precursor cell, forming an autoregulatory loop.

Organelles – understanding noise and heterogeneity in cell biology at an intermediate scale

“…2). For example, the budding yeast Saccharomyces cerevisiae exhibits more-than-random asymmetrical partitioning, where mitochondria are evenly partitioned between the mother and bud cells during cell division, despite the bud cell being significantly smaller in volume (Boldogh et al, 2001). In contrast, studies of GFPtagged Golgi complexes in HeLa cells show less-than-random asymmetrical partitioning, a phenomenon attributed to the association of Golgi complexes into mitotic clusters that lower the overall number of units of distribution (Shima et al, 1997).…”

“…Some partitioning events are clearly not random, as evidenced by the near 1:1 segregation of chromosomes and centrosomes during mitosis. However, other organelles, such as mitochondria and endosomes, are known to exhibit asymmetrical partitioning (Boldogh et al, 2001;Catlett and Weisman, 2000;Knoblach and Rachubinski, 2015). Interestingly, asymmetrical partitioning can produce distributions both more and less unequal than that predicted by binominal statistics (Fig.…”

“…A common source of directed heterogeneity is asymmetrical cell division, in which a cell divides to produce two daughter cells of differing fates. A classic example of this type of deterministic heterogeneity is found in Drosophila melanogaster development, where ganglion mother cells consistently undergo asymmetric division to give rise to two daughter cells -a larger cell that will become a motor neuron and a smaller sibling cell of unspecified developmental fate (Bhat et al, 2014).…”

Dynamic Notch Signaling Specifies Each Cell Fate inDrosophilaSpermathecal Lineage

“…The fact that ACs, BCs, and SCs have different cell size may also indicate the involvement of asymmetric cytokinesis in this lineage. The size difference also seems influenced by Notch signaling, similar to its role in asymmetric cleavage in neural precursor cells (Bhat 2014). Future work will be required to understand what determines the asymmetry and where the ligand source is for Notch signaling.…”

The glycosylation pathway is required for the secretion of Slit and for the maintenance of the Slit receptor Robo on axons

“…Immunochemistry was carried out as described previously (4, 25, 37). Monoclonal antibodies recognizing the following proteins were used at the indicated concentrations: Fas II [1:20, mouse monoclonal 1D4; Developmental Studies Hybridoma Bank (DSHB)], Slit-C (1:20, mouse, C555.6D; DHSB), Robo1 (1:3, mouse, 13C9; DHSB), and Robo3 (1:3, mouse, 14C9; DHSB).…”