Implications for interrelationships between nuclear architecture and control of gene expression under microgravity conditions

Components of nuclear architecture ape functionally interrelated with contr ol of gene expression. There is growing appreciation that multiple levels o f nuclear organization integrate the regulatory cues that support activatio n and suppression of genes as well as the processing of gene transcripts. T he linear representation of genes and promoter elements provide the potenti al for responsiveness to physiological regulatory signals. Parameters of ch romatin structure and nucleosome organization support synergism between act ivities at independent regulatory sequences and render promoter elements ac cessible or refractory to transcription factors. Association of genes, tran scription factors, and the machinery for transcript processing with the nuc lear matrix facilitates fidelity of gene expression within the three-dimens ional context of nuclear architecture. Mechanisms must be defined that coup le nuclear morphology with enzymatic parameters of gene expression. The rec ent characterization of factors that mediate chromatin remodeling and ident ification of intranuclear targeting signals that direct transcription facto rs to subnuclear domains where gene expression occurs link genetic and stru ctural components of transcriptional control. Nuclear reorganization and ab errant intranuclear trafficking of transcription factors for developmental and tissue-specific control occurs in tumor cells and in neurological disor ders. Compromises in nuclear structure-function interrelationships can occu r as a consequence of microgravity-mediated perturbations in cellular archi tecture.