Embryonic stem cells assume a primitive neural stem cell fate in the absence of extrinsic influences

Abstract

The mechanisms governing the emergence of the earliest mammalian neural cells during development remain incompletely characterized. A default mechanism has been suggested to underlie neural fate acquisition; however, an instructive process has also been proposed. We used mouse embryonic stem (ES) cells to explore the fundamental issue of how an uncommitted, pluripotent mammalian cell will self-organize in the absence of extrinsic signals and what cellular fate will result. To assess this default state, ES cells were placed in conditions that minimize external influences. Individual ES cells were found to rapidly transition directly into neural cells, a process shown to be independent of suggested instructive factors (e.g., fibroblast growth factors). Further, we provide evidence that the default neural identity is that of a primitive neural stem cell (NSC). The exiguous conditions used to reveal the default state were found to present primitive NSCs with a survival challenge (limiting their persistence and proliferation), which could be mitigated by survival factors or genetic interference with apoptosis.

Leukemia Inhibitory Factor Promotes Neural Stem Cell Self-Renewal in the Adult Brain

“…This view is supported by recent findings showing that mouse ES cells plated in minimal conditions default to a neural fate and transform into LIF-dependent primordial NSCs, which in turn generate FGF2-dependent definitive NSCs (Smukler et al, 2006). In those experiments, LIF appears to maintain a population of primordial NSCs in an undifferentiated state by preventing additional neural differentiation of the ES cells (Smukler et al, 2006). LIF-dependent, primordial NSCs similar to those derived from ES cells have also been obtained from embryonic day 5.5 mouse neuroectoderm (Hitoshi et al, 2004), suggesting that the continuum from ES cells to NSCs described in In contrast, infusion of EGF before AraC has no effect on subsequent SVZ regeneration.…”

“…This view is supported by recent findings showing that mouse ES cells plated in minimal conditions default to a neural fate and transform into LIF-dependent primordial NSCs, which in turn generate FGF2-dependent definitive NSCs (Smukler et al, 2006). In those experiments, LIF appears to maintain a population of primordial NSCs in an undifferentiated state by preventing additional neural differentiation of the ES cells (Smukler et al, 2006).…”

An intrinsic mechanism of corticogenesis from embryonic stem cells

“…1). Thus, ESCs cultured in the absence of any added morphogen efficiently differentiate into neural cells, as described 15,16 , and follow a neuron-glia sequence highly reminiscent of cortical cells in vitro and in vivo 17 .…”

Derivation of neural precursor cells from human ES cells at 3% O2 is efficient, enhances survival and presents no barrier to regional specification and functional differentiation

“…10 Consequently, neuralisation protocols often contain antioxidants, which may increase the propensity to accumulate genetic mutations, or involve co-culture with stromal feeder layers. 2,6,7,[10][11][12] In addition, antagonism of the TGF-b signalling pathway has been shown to augment the efficiency of neural conversion and thereby increase survival; however, this can also influence the default identity of neural progenitors and potentially limit their ability to be directed towards defined cell types. 13,14 The importance of ROS in mediating cell death during neural conversion under routine culture at oxygen (O 2 ) levels of 20%, which is far removed from than that found under physiological conditions in the central nervous system (CNS), suggests higher oxygen tension may be deleterious to neural specification and differentiation.…”

“…5 However, significant cell death is observed under such serum-free, defined conditions. 6 The mechanism through which the cells die involves both apoptotic and parthanatic pathways, [6][7][8][9][10] accompanied by the generation of reactive oxygen species (ROS). 10 Consequently, neuralisation protocols often contain antioxidants, which may increase the propensity to accumulate genetic mutations, or involve co-culture with stromal feeder layers.…”