Molecular Cloaking of H2A.Z on Mortal DNA Chromosomes During Nonrandom Segregation

Abstract

Although nonrandom sister chromatid segregation is a singular property of distributed stem cells (DSCs) that are responsible for renewing and repairing mature vertebrate tissues, both its cellular function and its molecular mechanism remain unknown. This situation persists in part because of the lack of facile methods for detecting and quantifying nonrandom segregating cells and for identifying chromosomes with immortal DNA strands, the cellular molecules that signify nonrandom segregation. During nonrandom segregation, at each mitosis, asymmetrically selfrenewing DSCs continuously cosegregate to themselves the set of chromosomes that contain immortal DNA strands, which are the oldest DNA strands. Here, we report the discovery of a molecular asymmetry between segregating sets of immortal chromosomes and opposed mortal chromosomes (i.e., containing the younger set of DNA template strands) that constitutes a new convenient biomarker for detection of cells undergoing nonrandom segregation and direct delineation of chromosomes that bear immortal DNA strands. In both cells engineered with DSC-specific properties and ex vivo-expanded mouse hair follicle stem cells, the histone H2A variant H2A.Z shows specific immunodetection on immortal DNA chromosomes. Cell fixation analyses indicate that H2A.Z is present on mortal chromosomes as well but is cloaked from immunodetection, and the cloaking entity is acid labile. The H2A.Z chromosomal asymmetry produced by molecular cloaking provides a first direct assay for nonrandom segregation and for chromosomes with immortal DNA strands. It also seems likely to manifest an important aspect of the underlying mechanism(s) responsible for nonrandom sister chromatid segregation in DSCs.

Histone Variants and Epigenetics

“…This observation is consistent with the fact that the H2A.Z gene is a target of Oct4 regulation and is down-regulated following differentiation of both mouse and human stem cell populations (Du et al 2001;Shaw et al 2009;Huh and Sherley 2011). More striking, however, is the apparent asymmetric distribution of H2A.Z entirely to the immortal DNA strands segregating to the stem cell sister, as detected by immunofluorescence (Huh and Sherley 2011). This turns out to be because of the "cloaking" of the H2A.Z histones on the mortal-strand chromatids inherited by the differentiating sister cell.…”

“…There is experimental support for this "immortalstrand model" in a number of systems in which asymmetric self-renewal can be experimentally manipulated. Interestingly, histone H2A.Z expression is a biomarker for this immortal-strand inheritance (Huh and Sherley 2011). First, H2A.Z mRNA is down-regulated in the differentiating sister cell during asymmetric cell division.…”

Higher 5-hydroxymethylcytosine identifies immortal DNA strand chromosomes in asymmetrically self-renewing distributed stem cells

“…xanthine | tricarboxylic acid cycle | alpha-ketoglutarate | p53 | IMPDH II A lthough distributed stem cells (DSCs) are universally essential for normal tissue function, health, and longevity (1)(2)(3)(4)(5), understanding of the cellular mechanisms responsible for their unique tissue functions is quite limited. In particular, the mechanisms responsible for the defining properties of DSCsasymmetric self-renewal (ASR) and nonrandom sister chromatid segregation-are unknown.…”

Adrien Albert Award: How to Mine Chemistry Space for New Drugs and Biomedical Therapies

“…Changes in cellular properties such as Modified with permission from Huh and Sherley. [55] adhesion, morphology, motility, gene expression, and differentiation are influenced by chemistry, wettability, topography, and elastic modulus of the surface on which they are cultured. Using a 496-member polymer library, Yang et al determined the degree of attachment of human embryonic stem cell embryoid bodies.…”