Masking, extrinsicness, and the nature of dispositions: the role of niche signals in muscle stem cells

I investigate the intrinsic/extrinsic nature of stemness in muscle stem cells (MSC) by relying on recent research on quiescence, with the aim of shedding light on the nature of dispositions and deriving some consequences about stem cells. First, I argue why the study of quiescence is the best available way to establish any claim about the intrinsicness/extrinsicness of stemness at least is some stem cells. Drawing on that, I argue that MSC’s stem capacities result from the combination of intrinsic cues plus extrinsic factors from the stem cell niche, making stemness an extrinsic disposition in MSC. Importantly, it is shown that the niche allows the instantiation of stemness in MSC by acting as a masker of its manifestation. This shows that stemness is, at least in MSC, what I call an extrinsically structurally masked disposition (SMD); that is, a disposition whose instantiation requires, as a condition of possibility, the interaction between the bearer and a masker. Finally, I conclude by suggesting some potential consequences of this observation for the philosophical study of dispositions and for stem cell research.