Topo-embryology: DNA Evolution from Ring to String Brings the Multi-cellar System

This paper clarifies the reason why microorganisms have ring-like DNA while multi-cell systems have string-like DNA. First, we show the driving force behind the stable morphogenetic process, which is examined in terms of both molecular biology and computational fluid-dynamics. An important point is that the cell-dividing contractile ring shrunk around string-like DNA will form an elliptic curve rather than a perfect circle, because it touches the edge of the string-like DNA, although ring-like DNA induces a circular contractile ring during shrinking. The change in DNA shape determines the shape of a contractile ring after it shrinks. The jet flow generated vertical to the shrinking surface of a contractile ring must also be examined. As the viscosity of water generates the shrinking flow around a contractile ring, the change in the contractile ring shape as it shrinks varies the jet flow inside the cell. The changed flow field carries the next contractile ring to a different displacement. The strong anisotropy of string-like DNA varies the spatial displacement of the next contractile ring generated from the DNA. This scenario corresponds to the fact that the DNA strings of multi-cell systems are displaced on a surface anisotropically in many cases.