2 Differentiated Parental DNA Chain Causes Stem Cell Pattern of Cell-type Switching in Schizosaccharomyces pombe

Abstract

According to the rules of Mendelian genetics, sister chromatids are equivalent, and genes are composed of DNA alone. Violations to both of these rules have been discovered, which explain the stem-cell-like pattern of asymmetric cell division in the fission yeast Schizosaccharomyces pombe. In this review, I highlight key ideas and their experimental support so that the reader can contrast these mechanisms, which are not based on differential gene regulation, with those discovered in other diverse systems presented in this monograph.

FISSION YEAST AS A MODEL SYSTEM FOR INVESTIGATING CELLULAR DIFFERENTIATION AT THE SINGLE-CELL LEVEL
S. pombe is a haploid, unicellular, lower eukaryotic organism whose genetics has been studied very thoroughly. Its genome comprises only three chromosomes, with DNA content similar to that of the evolutionarily distantly related budding yeast, Saccharomyces cerevisiae. This organism has been exploited as a major system for cell cycle studies as well as for studies of cellular differentiation. The single cells of fission yeast express either P (Plus) or M (Minus) mating-cell type and divide by fission of the parental cell to produce rod-shaped progeny of nearly equal size. Yeast cells do not express mating type while growing on rich medium. Only when they are starved, especially for nitrogen, do cells express their mating type and mate with cells of opposite type to produce transient zygotic diploid cells. Normally, the zygotic cell immediately enters into the meiotic cell division cycle and gives rise to four haploid spore segregants, two of P type and two of M...