Gene gating: a hypothesis.

It is assumed that the genome of a higher eukaryotic organism is organized into a number of distinct three-dimensional (3-D) structures, each characteristic for a given differentiated state. These discrete 3-D structures are envisioned to develop in a hierarchical and largely irreversible manner from an omnipotent 3-D structure of the zygotic genome. The information for these processes is assumed to reside in the genome. The nuclear pore complexes, the peripheral nuclear lamina, and components of the nuclear core are proposed to be among the topologically most proximal organelles that interpret this information and thereby serve in the maintenance and the alteration of the 3-D structure of the genome during development, differentiation, and the cell cycle. The nuclear pore complexes are envisioned to serve as gene-gating organelles capable on interacting specifically with expanded (transcribable) portions of the genome. Their nonrandom distribution on the nuclear surface would reflect the underlying periodic organization of the genome into expanded and compacted domains, alternating with each other. All transcripts of a given gated gene would leave the nucleus by way of that pore complex to which the gene is gated. Implications for cell asymmetry and polarity are discussed and evolutionary considerations are presented.