Isolation of novel cDNA encompassing the ADU balanced translocation break point in the DiGeorge critical region

Abstract

DiGeorge syndrome (DGS) is a developmental field defect of the third and fourth pharyngeal pouches that are associated with congenital heart defects, hypoparathyroidism, cell-mediated immunodeficiency, velopharyngeal insufficiency, and craniofaial anomalities. Approximately 90% of patients exhibit monosomy in the 22q11 region. In order to isolate the critical gene responsible for DGS, the cDNA libraries were screened with a probe containing the ADU balanced translocation break point, that is a locus reported in one patient (ADU) caused by a balanced translocation between chromosomes 22 and 2. Out of 10⁶ clones, three independent overlapping clones were isolated, which were assumed to have originated from a single transcript, DGCR7. This transcript contained a 175-aa long open reading frame (ORF), encoding an acidic (pI=5.81) and a proline-rich peptide, which are often found in the activation domain of several transcription factors. Also, it was predicted to be a nuclear protein. Northern hybridization detected an approx 1.9 kb transcript in all fetal and adult tissues tested, with strong expression in the fetal liver and kidney. In the case of adult tissues, strong expression was also detected in areas such as the heart, skeletal muscle, liver, and kidney.