Topic of the Month
Asymmetric cell divisions are characteristic of any occasion when the two daughters differ in fate, whether or not "stem cell" is one of the fates. In the case of the stem cell, the cell's first step must be to divide and to produce one daughter like itself, able to continue as a stem cell, and one daughter unlike itself, able to go down a path of differentiation. Much insight has recently been gained regarding mechanisms underlying asymmetric cell division in several different systems. The following papers give a very brief overview about the latest developments in this broadening field. For asymmetric cell division, both intrinsic cell fate programs and responses to extrinsic cues may be involved. In a thorough evolutionary survey of germline stem cells in metazoans, Extavour and Akam find that while in many model organisms preformation, a strategy using inherited determinants, seems to prevail, the strategy of inductive interaction is actually more often used, as for example in mammals. Mechanisms of germ cell specification across the metazoans: epigenesis and preformation. ABSTRACT Examples of Intrinsic Determination: Inherited determinants often direct fates of daughter cells, and for these daughters' fates to differ, their suite of inherited determinants must differ. A precursor to asymmetric cell division thus may be establishment of polarity within one cell. Cellular polarity may be stable, as in early embryos and perhaps in stem cells, or it may be a transient feature of the cell, called on for specific purposes. Polarity affects processes as diverse as bacterial chemotaxis, absorption of nutrients at the intestinal epithelium, axon guidance and oogenesis, as well as the generation of dissimilar daughter cells. A recent example is presented by Haecker et al. who describe the case in embryos of the small mustard-related plant Arabidopsis, where proteins of the WOX family (relatives of homeobox genes) are segregated at division of the zygote, with WOX2 going to the apical daughter cell that will generate shoot and leaf tissues, and WOX8 to the basal daughter that will generate roots. Expression dynamics of WOX genes mark cell fate decisions during early embryonic patterning in Arabidopsis thaliana. ABSTRACT
The planar cell polarity protein Strabismus promotes Pins anterior localization during asymmetric division of sensory organ precursor cells in Drosophila. ABSTRACT
Asymmetric inheritance of centrosomally localized mRNAs during embryonic cleavages. ABSTRACT
Asymmetric inheritance of oxidatively damaged proteins during cytokinesis. ABSTRACT There may also be other sorts of cues that direct daughter cells to different fates. In the case of Volvox, an asymmetric cell division generates cells different only by size, and then by as yet unknown mechanisms the size of the daughter cell leads to activation of either a somatic or germline program. Differentiation of germinal and somatic cells in Volvox carteri. ABSTRACT The question now becomes how all these molecules are distributed in an unequal fashion within the cell. In recent years much progress has been made regarding the shuttling of molecules through the cytoplasm. The cytoplasm, once believed to be a "liquid soup" filling the cell, is now seen to include a sophisticated railway system of microtubules on which molecules are moved in different ways to their destination. No surprise, then, that the microtubule system is critical for asymmetric cell division and distribution of molecules within the cell. Kusch et al. give an overview about how the spindle and microtubules, as well as certain highly conserved proteins, effect asymmetric division of cells. Spindle asymmetry: a compass for the cell. ABSTRACT
The minibrain kinase homolog, mbk-2, is required for spindle positioning and asymmetric cell division in early C. elegans embryos. ABSTRACT
Drosophila nonmuscle myosin II promotes the asymmetric segregation of cell fate determinants by cortical exclusion rather than active transport. ABSTRACT
Fluorescence bleaching reveals asymmetric compartment formation prior to cell division in Caulobacter. ABSTRACT
Drosophila PAR-1 and 14-3-3 inhibit Bazooka/PAR-3 to establish complementary cortical domains in polarized cells. ABSTRACT
A mechanism for polar protein localization in bacteria. ABSTRACT Examples of Extrinsic Influences: As mentioned in the beginning, the strategy of inductive signaling from surrounding tissues is a mechanism frequently used to direct asymmetric division. A good example are the stem cell niches in the Drosophila testes and ovaries. In the testes, cells that retain a physical attachment to the hub, a cluster of somatic cells, also retain identity as stem cells. Those cells that cytokinesis places away from the hub, without physical attachment, are launched off into the big wide world of spermatogenesis. Yukiko et al. add to this picture by showing that the stem cell uses the APC tumor suppressor protein to orient the mitotic spindle perpendicular to the hub, thus ensuring a cell division that will place one daughter near, and one daughter away from, the hub. Orientation of asymmetric stem cell division by the APC tumor suppressor and centrosome. ABSTRACT
Dpp signaling silences bam transcription directly to establish asymmetric divisions of germline stem cells. ABSTRACT
Aguilaniu, H., Gustafsson, L., Rigoulet, M., and Nystrom, T. (2003):
Bellaiche Y, Beaudoin-Massiani O, Stuttem I, Schweisguth F (2004): Benton R and Johnston DS (2003). Cell 115:691. Chen and McKearin (2003): Extravour CG and Akam M (2003): Haecker A, Gross-Hardt R, Geiges B, Sarkar A, Breuninger H, Herrmann
M, LauxT (2004): Howard M (2004): Judd EM, Ryan KR, Moerner WE, Shapiro L, McAdams HH (2003): Kusch, J., Liakopoulos, D., and Barral, Y. (2003): Lambert, J. D., and Nagy, L. M. (2002): Ming Pang K, Ishidate T, Nakamura K, Shirayama M, Trzepacz C, Schubert
CM, Priess JR, Mello CC (2004): Schmitt R. (2003): Yamashita, Y. M., Jones, D. L., and Fuller, M. T. (2003): Updated: March 18, 2004 |
||
| Disclaimers | Privacy Information | Contact Us | Site Map |
Asymmetric
Cell Division|
Member Login Username Password  |
|
