• Id helix-loop-helix proteins in cell growth and differentiation.

      Norton, John D; Deed, Richard W; Craggs, Graham; Sablitzky, F; Cancer Research Campaign Dept of Gene Regulation, Paterson Institute for Cancer Research, Christie Hospital NHS Trust, Manchester, UK. JNorton@picr.man.ac.uk (1998-02)
      Id helix-loop-helix proteins function at a general level as positive regulators of cell growth and as negative regulators of cell differentiation. They act as dominant-negative antagonists of other helix-loop-helix transcription factors, which drive cell lineage commitment and differentiation in diverse cell types of higher eukaryotes. In addition, the functions of Id proteins are integrated with cell-cycle-regulatory pathways orchestrated by cyclin-dependent kinases and the retinoblastoma protein. Here, some of the recent advances that highlight the importance of Id proteins as regulatory intermediates for coordinating differentiation-linked gene expression with cell-cycle control in response to extracellular signalling are reviewed.
    • Stage- and subcellular-specific expression of Id proteins in male germ and Sertoli cells implicates distinctive regulatory roles for Id proteins during meiosis, spermatogenesis, and Sertoli cell function.

      Sablitzky, F; Moore, A; Bromley, Michael; Deed, Richard W; Newton, J S; Norton, John D; Department of Medicine, The Windeyer Institute of Medical Sciences, University College London, United Kingdom. f.sablitzky@ucl.ac.uk (1998-12)
      Immunohistological detection of each of the four Id proteins (Id1-Id4) in sections of mouse testis revealed a unique temporal and spatial expression pattern for each Id protein during spermatogenesis. Furthermore, each Id protein displayed a distinctive, dynamic pattern of subcellular distribution. Id1 was uniquely expressed in MI/MII spermatocytes undergoing meiotic division. Id4 protein was detectable in the cytoplasm of type A1 spermatogonia, as well as in late pachytene and in diplotene spermatocytes. Id2 protein, which was most abundant in Sertoli cell nuclei, was also detectable in pachytene and diplotene spermatocytes, but as with Id4, it was absent from MI/MII cells. In postmeiotic spermatids, Id1, Id2, and Id4 proteins were expressed in a stage- and subcellular-specific manner. Expression of Id3 was restricted to Sertoli cell cytoplasm. In malignant seminoma cells, all four Id proteins were abundantly expressed with accompanying changes in their subcellular distribution. The observed expression of Id proteins in postproliferative Sertoli cells and spermatids and during specific stages of meiosis implies novel functional roles for this class of transcriptional regulator during spermatogenesis.