© 7995 Oxford University Press Human Molecular Genetics, 1995, Vol. 4, No. 11 2033-2045 Molecular characterization and chromosomal localization of DRT (EPHT3): a developmental^ regulated human protein-tyrosine kinase gene of the EPH family Naohiko Ikegaki 14 *, Xao X.Tang 2 , Xing-Ge Liu 1 , Jaclyn A.Biegel 3 - 4 , Cindy Allen 3 , Akira Yoshioka 2 , Erik P.Sulman 1 , Garrett M.Brodeur 14 and David E.Pleasure 2 Divisions of 'Oncology, 2 Neurology Research and 3 Human Genetics and Molecular Biology, The Children's Hospital of Philadelphia, Abramson Research Center, 902F, 324 South 34th Street, Philadelphia PA 19104-4318 and 4 Department of Pediatrics, University of Pennsylvania, School of Medicine, Philadelphia PA 19104, USA Received May 18, 1995; Revised and Accepted August 11, 1995 By screening a human fetal brain cDNA expression library using a monoclonal antiphosphotyrosine anti- body and by 5' RACE procedures, we have isolated overlapping cDNAs encoding a receptor-type tyrosine kinase belonging to the EPH family, DRT (Develop- mentally Regulated EPW-related 7yrosine kinase gene). The DRT gene is expressed in three different size transcripts (i.e. 4, 5 and 11 kb). DRT transcripts are expressed in human brain and several other tissues, including heart, lung, kidney, placenta, pancreas, liver and skeletal muscle, but the 11 kb DRT transcript is preferentially expressed in fetal brain. Steady-state levels of DRT mRNA in several tissues, including brain, heart, lung and kidney, are greater in the midterm fetus than those in the adult. DRT transcripts are detectable at low levels in a human teratocarcinoma cell line (NTera-2), but its expression is greatly increased after the NTera-2 cells are induced to become postmitotic neurons (NTera- 2N) by retinoic acid treatment. These data suggest that DRT plays a part in human neurogenesis. A large number of tumor cell lines derived from neuroectod- erm express D/?rtranscripts, including 12 neuroblas- tomas, two medulloblastomas, one primitive neuro- ectodermal tumor and six small cell lung carcinomas (SCLC). Interestingly, several neuroblastoma cell lines with 1p deletion and one SCLC cell line express DRT transcripts of aberrant size (i.e. 3, 6 and 8 kb) in addition to those found in normal tissues. We mapped the DRT gene to human chromosome 1p35-1p36.1 by PCR screening of human-rodent somatic cell hybrid panels and by fluorescence in situ hybridiza- tion. As the distal end of chromosome 1p is often deleted in neuroblastomas and altered in some cases in SCLCs, these chromosomal abnormalities may have resulted in the generation of aberrant size tran- scripts. Thus, the DRT gene may play a part in neuroblastoma and SCLC tumorigenesis. INTRODUCTION Protein tyrosine kinases (PTKs) have been known to be involved in fundamental biological processes such as regulation of normal cell growth, differentiation and survival (I-3). Recent studies have revealed that cell fate determination during development is also regulated through the interaction between receptor-type tyrosine kinases and their ligands (4-7). Indeed, mutations of PTK genes have been linked to several human diseases, including hereditary disorders, developmental defects (8-16) and cancer (17-28). We have been interested in studying the role of receptor- type tyrosine kinases in normal development of the nervous system and their possible involvement in hereditary/congenital neurological disorders as well as in the tumorigenesis of neuroectodermal cells. In order to study these issues, we first attempted to identify functionally PTKs expressed in the nervous system by screening a human fetal brain cDNA expression library using an antiphosphotyrosine antibody. We found that the majority of PTK clones obtained by our screening belong to the EPH family receptor-type PTK genes. This high frequency of ZT/W-family gene expression in the human fetal brain, in turn, suggested that EPH family PTKs play an important part in normal development of the nervous system. Alterations and/or mutations of the EPH family PTK genes, thus, may lead to neurological disorders and/or cancer of the nervous system. The EPH gene was first identified by screening a human genomic library with gene sequences homologous to the tyrosine kinase domain of a viral oncogene, \-fps (29). Analysis of deduced amino acid sequence and predicted structure of the EPH gene product suggested that it is a receptor-type PTK and has unique features that distinguish it from other known receptor PTKs (29). To date, many EPH-related tyrosine kinases have been identified in different species including zebrafish, Xenopus, chicken, mouse, rat and human (29-46). *To whom correspondence should be addressed Downloaded from https://academic.oup.com/hmg/article/4/11/2033/655201 by guest on 08 March 2021