Owen M. Rennert, MD, Chief

The Laboratory of Clinical Genomics (LCG) focuses on the interface between biological and clinical research dealing with the process of development/differentiation.

The Section on Developmental Genomics, led by Owen Rennert, established a database of germ cell genes. Unsupervised cluster analyses of the genes identified biological processes that occur preferentially at specific stages of spermatogenesis. The Section also identified promoter modules that regulate stage-specific expression of genes and constructed signature networks of each cell stage that linked cell-specific gene candidates with neighboring genes, proteins, transcription factors, and small molecules. The networks enable targeting of selected stages in spermatogenesis for intervention or enhancement. The SAGE database also provided the platform for the discovery of stage-specific alternative splicing of a number of genes. The Section found 73 genes that produce 3´ end alternative splicing variants specific for type A spermatogonia, pachytene spermatocytes, and round spermatids. The factors that enable stage-specific splicing and the biological activities of the splicing variants are under investigation. The database also provided leads for the identification of a network of anti-sense transcripts that are abundantly expressed in germ cells. The Section cloned several anti-sense transcripts, and their characterization revealed a wide spectrum of mechanisms by which they arise. Using in vitro cell models, the interactions between sense and anti-sense transcripts are under investigation.

Earlier research had identified a large number of novel genes differentially expressed at different stages of germ cell development. Molecular cloning and characterization of some of the genes led to the identification of several Lin28 transcripts with variable transcription start sites and 3´ untranslated regions. Studies are in progress to investigate the factors that contribute to the expression of selected variants. Cloning of the full-length cDNA of a novel gene confirmed that the gene encodes a new testis-specific isoform of the murine N-terminal acetyltransferase 1, mARD2. The biological activity of mARD2 in spermatogenesis is currently under investigation.

In addition to studying normal germ cell development, members of the Section investigated epigenetic changes associated with testicular germ cell tumor development and, using CpG island chips, examined changes in the global methylation pattern of testicular tumor cell lines and tumor tissues, including the effect of the TSPY oncogene on gene expression. To understand gene expression and regulation in early gonadal development, the researchers used SAGE to map the transcriptomes of embryonic gonads of male mice and thus identified several genes that are expressed in embryonic gonads but not in differentiated germ cells. They also initiated a functional genomic study of gonad and brain development, a study that is an outgrowth of their investigations of the neuronal effects of luteinizing hormone receptor (hLHR) mutations. The researchers identified a novel activity of the constitutively activated hLHR that enhances neurite outgrowth and examined the effects of inactivating mutations of hLHR.

In collaboration with Drs. Gahl (NHGRI) and Kaiser (NEI), members of the Section also examined patients with nephropathic cystinosis and susceptibility to thromboses that might predispose them to developing pseudo-tumor cerebri. To facilitate the detection of individuals at risk for venous thrombosis, researchers are studying a new screening device that will allow rapid screening of mutations and polymorphisms reported to be risk factors for the development of the disorder.

During the past year, the Unit on Pediatric Genetics, led by Stephen Kaler, has investigated two groups of disorders: the X-linked recessive disorder called Menkes Kinky Hair disease and the platelet abnormality known as Bernard-Soulier syndrome. In the case of Menkes Kinky Hair disease, the Unit investigated gene-expression consequences of a defect in the copper-ATP7A transport system in clinical autopsy material and used a yeast complementation assay to assess residual copper transport capacity by specific Menkes disease (ATP7A) mutant alleles. The investigators studied a child who had the velo-cardio-facial syndrome with thrombocytopenia due to haploinsufficiency of chromosome 22q11. Their research led to the further delineation of the GPIb alpha-GPIb beta-GPIX platelet glycoprotein complex.