ELSEVIER Molecular Brain Research 30 (1995) 312-326 MOLECULAR BRAIN RESEARCH Research report Id gene expression during development and molecular cloning of the human Id-1 gene Weijia Zhu a John Dahmen a Alessandro Bulfone b, Muriel Rigolet a Maria-Clemencia Hernandez a, Wen-Lin Kuo c, Luis Puelles d, John L.R. Rubenstein b, Mark A. Israel a,, a Preuss Laboratory, Brain Tumor Research Center of the Department of Neurological Surgery, San Francisco, CA 94143, USA b Nina Ireland Laboratory of Developmental Neurobiology and the Center for Neurobiology and Psychiatry, San Francisco, CA 94143, USA c Department of Laboratory Medicine, School of Medicine, University of California, San Francisco, CA 94143, USA d Department of Morphology, University ofMurcia, Murcia, Spain Accepted 17 January 1995 Abstract Id genes encode helix-loop-helix proteins that inhibit transcription by forming inactive heterodimers with basic helix-loop-helix (bHLH) proteins, bHLH proteins normally form either homodimers or heterodimers with other bHLH proteins and bind to a DNA sequence element activating transcription. Id-containing heterodimers are inactive because Id proteins lack the basic amino acid region necessary to form a DNA-binding domain. We have examined the relative levels of Id-1 and Id-2 mRNA during normal development and in malignant tissues. In the course of these experiments we cloned and sequenced the human Id-1 cDNA. Two related cDNA molecules encoding human Id-1 mRNAs were identified. Id-la is a cDNA of 958 nucleotides and can encode a protein of 135 amino acids. Id-lb cDNA is 1145 nucleotides, can encode a protein of 149 amino acids, and appears to be a splice variant of Id-la. The amino acid sequence of human Id-1 is greater than 90% homologous to that of mouse Id-1. The patterns of Id-1 and Id-2 expression during mouse development vary widely, and we detected Id-1 expression in human fetal and adult tissues from lung, liver, and brain. High Id-1 mRNA expression was found in many human tumor cell lines, including those isolated from nervous system tumors. We mapped Id-2 to human chromosome 2p25. Keywords: Id gene; bHLH protein; Gene expression 1. Introduction HLH (helix-loop-helix) proteins are a large family of transcription factors that have been implicated in the developmental control of gene expression and cell dif- ferentiation [37,38]. One class of such transcription factors, the bHLH (basic helix-loop-helix) proteins, binds to a specific DNA enhancer element known as an E-box, CANNTG, utilizing a region of basic amino acids immediately N-terminal to the HLH motif [6,38,39]. bHLH proteins always bind to DNA either as a homodimer or as a heterodimer formed by complex- ing with another bHLH protein [29]. E-box DNA se- quences can bind ubiquitously expressed bHLH * Corresponding author. Fax: (1) (415) 476-0388. 0169-328X/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSDI 0169-328X(95)00017-8 molecules as well as tissue-specific bHLH factors that have been implicated in the regulation of tissue-specific gene expression [30,47,52]. bHLH proteins ubiquitously expressed in many tissues include the products of the E2A gene, El2 and E47 [37]; the family of myc-related genes; and other widely-expressed transcription factors such as USF [22], HEB [25], TFE3 [3], ITF2 [24], TFEB [48] and AP4 [26]. Other bHLH proteins are expressed in mammalian cells in a tissue-specific manner and found in muscle (MyoD, myogenin, Myf-5) [48], neu- ronal tissue (HEN1 and HEN2) [7], and lymphoid tissue (TALl, TAL2, and LYL1) [32,36,53]. In mammalian ceils, the bHLH transcription factors that have been studied most thoroughly are expressed in a tissue-specific manner and control tissue-specific gene expression. MyoD, myogenin, and the Myf genes encode bHLH proteins that control muscle-specific genes in differentiating muscle cells. During muscle