Cloning and functional studies of a novel gene aberrantly expressed in RB-deficient embryos.
The tumor suppressor RB regulates diverse cellular processes such as G1/S transition, cell differentiation, and cell survival. Indeed, Rb-knockout mice exhibit phenotypes including ectopic mitosis, defective differentiation, and extensive apoptosis in the neurons. Using differential display, a novel gene, Rig-1, was isolated based on its elevated expression in the hindbrain and spinal cord of Rb-knockout embryos. The longest open reading frame of Rig-1 encoded a polypeptide that consists of a putative extracellular segment with five immunoglobulin-like domains and three fibronectin III-like domains, a putative transmembrane domain, and a distinct intracellular segment. The Rig-1 sequence was 40% identical to the recently identified roundabout protein. Consistent with the predicted transmembrane nature of the protein, Rig-1 protein was present in the membranous fraction. Antisera raised against the putative extracellular and intracellular segments of Rig-1 reacted with an approximately 210-kDa protein in mouse embryonic CNS. Rig-1 mRNA was transiently expressed in the embryonic hindbrain and spinal cord. Elevated levels of Rig-1 mRNA and protein were found in Rb-/- embryos. Ectopic expression of a transmembrane form of Rig-1, but not the secreted form, promoted neuronal cell entrance to S phase and repressed the expression of a marker of differentiated neuron, Talpha1 tubulin. Thus Rig-1, a possible distant relative of roundabout, may mediate some of the pleiotropic roles of RB in the developing neurons.
Department of Molecular Medicine/Institute of Biotechnology, University of Texas Health Science Center at San Antonio, San Antonio, Texas, 78245, USA.
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Yuan
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Cox
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Dasika
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Lee
D017398:Alternative Splicing / Q000235:genetics; D000595:Amino Acid Sequence; D000818:Animals; D002453:Cell Cycle / Q000235:genetics; D002490:Central Nervous System / Q000196:embryology / Q000254:growth & development; D003001:Cloning, Molecular; D005314:Embryonic and Fetal Development; D005455:Fluorescent Antibody Technique; D018507:Gene Expression Regulation, Developmental / Q000235:genetics*; D007136:Immunoglobulins / Q000235:genetics; D017403:In Situ Hybridization; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics*; D051379:Mice; D018345:Mice, Knockout; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics; D011956:Receptors, Cell Surface; D011971:Receptors, Immunologic / Q000235:genetics; D016160:Retinoblastoma Protein / Q000235:genetics*; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D000097905:Roundabout Proteins
D007136:Immunoglobulins; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; D011971:Receptors, Immunologic; D016160:Retinoblastoma Protein; D000097905:Roundabout Proteins; C118348:Robo3 protein, mouse