Asymmetric cell divisions

All mature blood cells arise from primitive hematopoietic cells in the bone marrow, the pluripotent stem cells. Approximately 0.1% of the nucleated cells of the bone marrow are pluripotent stem cells and approximately 5% of these cells may be actively cycling at any one time. The stem cell pool maintains itself through a process of asymmetrical cell division when a stem cell divides, one daughter cell remains a stem cell and the other becomes a committed colony-forming cell (CFC). The proliferation and differentiation of CFCs are controlled by hematopoietic growth factors. The hematopoietic growth factors stimulate cell division, differentiation and maturation, and convert the dividing cells into a population of terminally differentiated functional cells. 

A third justifreation for studying the eell eycle of this yeast is that it afiords a convenient system in which to study cell polarity. Together with asymmetric cell division (irrherent in the S. cerevisiae cell cyele with the unequal sized mothers and daughters), the development of polarity is emeial in many aspects of development and differentiation. Furthermore, as explained in more detail later in this chapter, the correct... 

The cell cycle machinery and asymmetric cell division of neural progenitors in the Drosophila embryonic central nervous system... 

Asymmetric cell division is a universal mechanism utilized for the generation of cellular diversity during development (for reviews see Horvitz Herskowitz 1992, Guo Kemphues 1996, Shapiro Losick 1997, Jan Jan 1998). Asymmetric cell divisions during Drosophila embryonic development involve both extrinsic cues mediated through Notch and Delta and intrinsic cell fate determinants and play a major role in producing the distinct cell types which are... 

FIG. 1. Localization of key proteins involved in the neuroblast asymmetric cell division. During late interphase a complex of proteins including Insc, Baz (and Pins) are localized to the apical cell cortex. This complex acts to mediate the basal cortical localization of the cell fate determinants Numb (and its partner Pon), Pros (and its partner Miranda) and pros RNA (and its partner Staufen) during mitosis. During interphase, Numb is cytoplasmic and Pros is localized to the apical cortex. 

Maintenance of the apical complex is necessary for all aspects of asymmetric cell division... 

In Pins - embryos the initiation steps of apical complex formation occur normally. However, this complex cannot be maintained in mitotic neuroblasts. Hence, the importance of the maintenance of this complex for asymmetric cell division can be ascertained by assessing how Pins- neural progenitors divide. Pins- embryos exhibit all of the defects seen in insc mutants. Mitotic spindle orientation is defective. In the cells of mitotic domain 9 the 90° reorientation, which normally occurs in wild-type resulting in the orientation of the spindle along the apical—basal axis (Fig. 3A), fails to occur in the mutant (Fig. 3B). Mitotic spindle orientation of neuroblasts in the segmented CNS, deduced from DNA staining, also often fails to... 

To see whether similar defects in asymmetric cell divisions and protein localization can be seen in other cdc2 mutant combinations, we used a stock... 

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Kaltschmidt JA, Davidson CM, Brown NH, Brand AH 2000 Rotation and asymmetry of the mitotic spindle direct asymmetric cell division in the developing central nervous system. Nat Cell Biol 2 7-12... 

Tio M, Zavortink M, Yang X, Chia W 1999 A functional analyses of inscuteable and its roles during Drosophila asymmetric cell divisions. J Cell Sci 112 1541—1551 Uemura T, Shepherd S, Ackerman L, Jan LY, Jan YN 1989 numb, a gene required in determination of cell fate during sensory organ formation in Drosophila embryos. Cell 58 349-360... 

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Ambrose Do you have any evidence for the pars or gyg-8 acting later in development, for example in postembryonic asymmetric cell divisions ... 

Brummendorf TH, Dragowska W, Zijlmans JMJM, Thornbury G, Lansdorp PM. Asymmetric cell divisions sustain long term hematopoiesis from single-sorted human fetal liver cells. J.Exp.Med. 1998 188 1117 1124. 

SWI/SNF PSA-4 C. elegans PSA-1 Required for asymmetric cell division during C. elegans development [272]. 

Bellaiche Y, Radovic A, Woods DF, Hough CD, Parmentier ML, O Kane CJ, Bryant PJ, Schweisguth F (2001) The Partner of Inscuteable/Discs-large complex is required to establish planar polarity during asymmetric cell division in Drosophila. Cell 106 355-366... 

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Polarity, Asymmetric Cell Division, and Morph ogens... 

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