Mouse chromosome 15

Committee Members: R. Duncan and J. Todd.     

Nitrogen Fixation in Continuous Culture with NH4Cl-Containing Media

N balance and ¹⁵N dilution were determined from growth of Azospirillum brasilense Sp7 and two unidentified gram-negative nitrogen-fixing microorganisms in continuous culture supplied with NH₄Cl. At the 1.1 and 2.2 mM NH₄Cl steady states (N-to-C ratios of 1:68 and 1:34, respectively), the organisms grew with NH₄Cl and N₂ as N sources simultaneously under carbon limitation. No ammonium could be detected in the supernatant of these cultures.     

Maternal serum alpha-fetoprotein screening activities of state health agencies: a survey.

Maternal serum alpha-fetoprotein (MSAFP) screening has been demonstrated to be cost-effective on a population basis and is becoming standard practice. The American Society of Human Genetics has twice published policy statements to define the essential elements of a quality screening program. The present study reviewed the impact of these policy statements on state public-health agencies with respect to regulation or provision of MSAFP screening in their jurisdictions. With a few exceptions, states have not elected to play a major role in provision or regulation of this test. There is need to address issues of funding, standards, and data collection in a collaborative effort, if policy statements on genetic services are to be translated into effective state population screening.     

A rapid scanning strip for tri- and dinucleotide short tandem repeats.

Oligonucleotides representing 60 trinucleotide (21mers) and four dinucleotide (20mers) tandem repeats were directly synthesized and arrayed onto an aminated polypropylene substrate. DNA samples of different complexities (a CAG-containing 21mer oligonucleotide, PCR fragments of 200 to 3,000 bp, and cosmids with 31 to 35 kb inserts) were radiolabelled and hybridized to the oligonucleotide array at various temperatures. When compared to sequence data available from the test DNAs, the reverse blot system specifically identified various tri- and dinucleotide short tandem repeats (STRs) in every case. Moreover, there was no random or cross hybridization to nonspecific sequences. It was possible to detect as few as three repeated units in a particular location, as shown for (CCT)n, (GCC)n and (CAC)n triplets in cosmid DNA. Varying the hybridization stringency can enhance the detection of STRs. This single-step reverse blot system therefore allows the rapid, specific and sensitive identification of various STRs in DNA sources of different complexity.     

Identifying differences in mRNA expression by representational difference analysis of cDNA.

Detection of differentially regulated genes has been severely hampered by technical limitations. In an effort to overcome these problems, the PCR-coupled subtractive process of representational difference analysis (RDA) [Lisitsyn, N. et al. (1993) Science 259, 946-951] has been adapted for use with cDNA. In a model system, RAG-1 and RAG-2, the genes responsible for activating V(D)J recombination, were identified in a genomic transfectant by cDNA RDA in a small fraction of the time taken by conventional means. The system was also modified to eliminate expected difference products to facilitate the identification of novel genes. Additional alterations to the conditions allowed isolation of differentially expressed fragments. Several caffeine up-regulated clones were obtained from the pre-B cell line 1-8, including IGF-1B, and a predicted homologue of the natural killer cell antigen, NKR-P1. The approach was found to be fast, extremely sensitive, reproducible, and predominantly lacked false positives. cDNA RDA has the capacity and adaptability to be applied to a wide range of biological problems, including the study of single gene disorders, characterization of mutant and complemented cell types, developmental or post-event expression time courses, and examination of pathogen-host interactions.