Asymmetric Division, Stem Cells and the Immortal Strand Hypothesis

Abstract

I have proposed a hypothetical mechanism for guiding the development of complex, multi-cellular organisms that relies only on coding intrinsic to each cell (The Master Development Program hypothesis in Biosciences Hypotheses 2:3-12. 2009).  An essential element in that mechanism is the ability of a de facto stem cell to differentiate into two different cell types and produce branches in the lines of cells without external cues or asymmetric environmental factors.  At this time, I want to focus on this important element in more detail because I have realized that although much research has been published on asymmetric division, very little of it focuses on the genome.  Moreover, the accepted mechanisms for asymmetric division imply that asymmetry is induced in the cytoplasm and that differentiation of the genomic programming follows asymmetric division.  In the mechanism I proposed and elaborate here, asymmetry is first induced in the tetraploid (G2) stage of the cell cycle of a de facto stem cell and then the cytoplasm responds to a new transcriptome.  The mechanism that I describe coincidentally supports the immortal strand hypothesis, which opines that the parental strand of DNA always ends up in the parental stem cell.  In the mechanism that I proposed and elaborate here, the parental DNA strand remains in the original stem cell because it defines the original stem cell, while the newly synthesized and differentially imprinted strand defines the character of a new cell type (the progenitor of a new cell line).