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The article posted for this thread suggests that stem cells later reach a stage where they have "committed" themselves to particular type of growth.
Is this what you are disputing? That once the cells became receptive to light they no longer fit the definition?
Correct. Once cells have 'differentiated' they are no longer stem cells. The cells in the title article are no longer stem cells. In fact, the authors mention that they will need a source for these cells from humans and they may possibly use either embryonic or adult stem cells for that source depending on future testing.
Using mice models, scientists have transplanted photoreceptor-precursor cells directly into the retina of the eyes, thus restoring visual function.
Rather than injecting undifferentiated and uncommitted stem cells into the retina in hopes they would develop into photoreceptors, researchers introduced cells at a somewhat later stage. These cells are referred to as "precursors": they are immature cells that are "programmed" to be, but have not yet become, functionally mature photoreceptors-the light-sensitive cells in the retina that are essential for sight.
An exact equivalent of this technique may be difficult to carry out in humans as photoreceptor-precursor cells will have to be sourced from fetuses. However, the authors suggest that such cells may be derived from adult of embryonic stem cells.
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