This position, meaning the microenvironment in which the cell comes to find itself, makes the cell more or less accessible to signaling factors that control differentiation.
In these cases, division orientation controls cell fate not through differential distribution of factors, but rather by dictating the position in which each daughter cell is born within the tissue. In other instances, cell fate determination is cell extrinsic ( Fig. 1). Cell intrinsic division asymmetry has also been observed in vertebrate systems, namely in T lymphocytes and embryonic stem cells ( Chang et al., 2007 Habib et al., 2013). In the mollusc Ilyanassa obsoleta, cell fate-determining mRNAs associate with one of the two centrosomes, and are thus differentially inherited ( Lambert and Nagy, 2002). A similar mechanism for asymmetric segregation of fate determinants has been observed in Drosophila neuroblasts and sensory organ precursor (pI) cells, and more recent work suggests that it also functions in Drosophila intestinal stem cells (reviewed by Knoblich, 2010 Morin and Bellaïche, 2011 Siller and Doe, 2009 see also Goulas et al., 2012 Guo and Ohlstein, 2015). For example, in the one-cell stage Caenorhabditis elegans embryo, cell fate factors are differentially localized at either the anterior or posterior of the cell, and the orientation of the spindle, along with its position along the anterior-posterior (A-P) axis, ensures that these factors are partitioned unequally (reviewed by Gönczy and Rose, 2005).
Multiple cell types use oriented divisions to direct this distribution. This can be a cell-intrinsic process that relies on the asymmetric distribution of cell fate factors, such that only one daughter cell inherits proteins or RNAs that determine its identity ( Fig. 1). The term ACD is typically used to mean that the two products of cell division have different fates. In particular, its importance for asymmetric cell division (ACD) has long been recognized. Spindle orientation plays a crucial role in animal development.
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