Analysis of Genome Operating Systems for Immune Network by Polycomb Group Genes.

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The Polycomb group (PcG) genes products form protein complexes in mammalian cell nuclei that contribute to maintain chromatin silencing of target genes. Among mammalian PcG homologues, mel-18 has been elucidated to regulate cell cycle progression, cell death, or senescence through analyses of knockout/Tg mice. Its product participatesin Polycomb protein complexes, whose existences in cell nuclei are displayed speckled distributions, overlapped with heterochromatin areas in immunohistochemical examinations.We describe that the defect in thymic T-lymphocyte development of mel-18 deficient mice implies the involvement of mel-18 in the maintenance of immature lymphocyte by regulating their survival via controlling the expression of some commitment and survival factors including subgroup of bcl-2 family. Therefore we would like to propose our results as the regulation mechanisms to control the balance between proliferation and cell death in lymphocyte development, especially ETP cell of DN1 fraction and small cell (E cell) of DN3 fraction just before the beta-selection of immature thymocyte by destabilization of chromatin silencing Polycomb protein complex.