Positional information and non-transcribed DNA.

Abstract

The spatial allocation of a cell in a multicelled organism is specified by positional information, and current theory proposes that the underlying mechanism is concerned with either global factors or local cell to cell cytoplasmic factors. However, neither of these mechanisms addresses the basic question of how positional information stored in the genes is converted into cell orientation. In this regard there are two options. One is the information in the gene to be translated by factors external to the nucleus, and the second is for the genetic information in the nucleus to be in the form of a spatial plan, and for the plan itself to act as the positioning agent. The second option could be achieved if a set of specific spatial points were encoded in the DNA of one nucleus and these points were to form a union with a corresponding set of points in the DNA of the nucleus to be joined, the spatial orientation of the points being such that the two nuclei are correctly aligned. The DNA of the nucleus is analysed from the point of view of these requirements, and it is shown that the non-transcribed DNA satisfies them. In order for spatial orientation to be a direct function of the DNA, nucleus to nucleus contact of the embryonic cells at the time of organogenesis is essential, and evidence is presented showing that not only contact is made but that the contact results in nucleus to nucleus fusion. The hypothesis is put that cell alignment is achieved by the matching up of spatial arranged loops in the DNA of adjacent nuclei, the spatial pattern of the loops being determined by the non-transcribed DNA. The hypothesis provides a molecular basis for cell alignment, and is used to explain certain puzzling features of embryogenesis. It is applicable to both the animal and plant kingdoms, but perhaps the main virtue of the hypothesis is that it represents a new approach to morphogenesis.