So while I deeply impressed by your theory Turnbuckle, but I am also a born skeptic. I understand our universe is not perfect, but what you present, is there some reasonable level of consensus? I opened two papers and I read something different, so appreciate your wisdom here:
Mito Dynamics: Fission and Fusion in fate determination of MSCs, Lin Ren et al, 2020. They contend that: "Active mitochondrial fission, adapted to glycolytic dependence on energy production, is critical for the self-renewal and pluripotency of MSCs",
2019: Mitochondrial fission is essential for maintaining stemness in MSCs, and inhibiting fission leads to a reduction in the expression of stemness markers and multidirectional differentiation potential (Feng et al., 2019)
While this may not be applicable to our scenario but still: 2016: "During somatic cell reprogramming to iPSCs, cells undergo mitochondrial reconstruction, usually from a mature network toward immature mitochondria, and a metabolic shift, usually from OXPHOS toward glycolysis. Drp1-dependent mitochondrial fission is also necessary for the acquisition of cellular pluripotency during the early stage of embryonic fibroblast induction to form iPSCs" (Prieto et al., 2016)
A one important concept the aforementioned paper is introducing: "However, over fission induced by Mff overexpression impairs the pluripotency of ESCs and iPSCs, suggesting that active fission should be within a certain threshold to better maintain stem cell function" I assume this concept would be applicable to MSCs / adult stem cells in our bodies as well?
Let's get on the same page with the terminology, as not everyone uses the same definitions.
Herein proliferation is symmetric division, or self-renewal. One SC becomes two SCs.
Differentiation is asymmetric division. One SC becomes one SC and one somatic cell.
Stemness is a long-term fundamental property of SCs. Without stemness, SCs will not be able to proliferate or differentiate.
The first paper you referenced is talking about fission being required for the maintenance of stemness in culture, not for proliferation in the sense I used above. Both fission and fusion are necessary for maintaining the health of all cells, not just SCs, and thus mitochondria are highly active, constantly fusing and fissioning.
Mitochondrial fusion is used herein to bias SCs to proliferation (one SC becoming two), while mito fission biases SCs for differentiation. See the following paper --
In this model, elongated [fused] mitochondria in NSCs maintain low ROS levels and promote self-renewal, while a transition of mitochondria to a more fragmented [fission] state results in a modest increase in ROS levels, thereby inducing the expression of genes that inhibit self-renewal (Botch) and promote commitment and differentiation
https://www.cell.com...20?showall=true
As an aside, I don't believe they are correct about lower ROS being the operative factor, for if it was, good antioxidants would make a substantial impact on viable SC levels and thus longevity, but they don't. This applies to C60 as well. It is an excellent antioxidant, but used without a fusion agent, if fails to extend lifespans. In my view a clue can be found in the first paper when they write about the "asymmetrical segregation of mitochondria" during differentiation. An asymmetry in the SC is needed for asymmetric division.
For example, it has been suggested that young mitochondria go to the new SC, while the old ones go to the new somatic cell.
Old mitochondria are preferentially segregated to the differentiating daughter, whereas stem cells inherited fewer older mitochondria during the asymmetric division of human mammary stem-like cells, suggesting that stem cells might be protected from senescence by eliminating old, nonfunctional mitochondria (Fig. 4 D; Katajisto et al., 2015).
https://www.ncbi.nlm...les/PMC6219723/
According to that paper, segregating mitochondria might be a benefit, but in my view, it is actually the fate determinant. By preventing segregation of mitochondria by fusing them, that would dampen any asymmetry, and without asymmetry you get proliferation.
Edited by Turnbuckle, 28 August 2022 - 01:13 AM.