A Family of DNA Sequences is Reproducibly Rearranged in the Somatic Nucleus of \u3cem\u3eTetrahymena\u3c/em\u3e

A small family of DNA sequences Is rearranged during the development of the somatic nucleus in Tetrahymena. The family is defined by 266 bp of highly conserved sequence which restriction mapping, hybridization and sequence analysis have shown is shared by a cloned micronuclear fragment and three sequences which constitute the macronuclear family. Genomic Southern hybridization experiments indicate there are five members of the family in micronuclear DNA. All of the family members are present in whole genome homozygotes and are therefore nonallellic. The three macronuclear sequences are all present in clonal cell lines and are reproducibly generated in every developing macronucleus. The rearrangement event begins 14 hours after conjugation is initiated and is nearly completed by 16 hours

Pan-ethnic carrier screening and prenatal diagnosis for spinal muscular atrophy: clinical laboratory analysis of >72 400 specimens

Spinal muscular atrophy (SMA) is a leading inherited cause of infant death with a reported incidence of ∼1 in 10 000 live births and is second to cystic fibrosis as a common, life-shortening autosomal recessive disorder. The American College of Medical Genetics has recommended population carrier screening for SMA, regardless of race or ethnicity, to facilitate informed reproductive options, although other organizations have cited the need for additional large-scale studies before widespread implementation. We report our data from carrier testing (n=72 453) and prenatal diagnosis (n=121) for this condition. Our analysis of large-scale population carrier screening data (n=68 471) demonstrates the technical feasibility of high throughput testing and provides mutation carrier and allele frequencies at a level of accuracy afforded by large data sets. In our United States pan-ethnic population, the calculated a priori carrier frequency of SMA is 1/54 with a detection rate of 91.2%, and the pan-ethnic disease incidence is calculated to be 1/11 000. Carrier frequency and detection rates provided for six major ethnic groups in the United States range from 1/47 and 94.8% in the Caucasian population to 1/72 and 70.5% in the African American population, respectively. This collective experience can be utilized to facilitate accurate pre- and post-test counseling in the settings of carrier screening and prenatal diagnosis for SMA

Micronucleus-Specific DNA Sequences in an Amicronucleate Mutant of Tetrahymena

DNA from the amicronucleate Tetrahymena cell line BI3840 was probed for DNA sequences which are limited to the micronucleus in wild-type cells. Four micronucleus-specific DNA sequences were not detectable in DNA from the amicronucleate cell line. Two of the six micronucleus-specific DNA sequences tested hybridized to DNA from amicronucleate cells. Both the number of fragments homologous to these sequences and the intensity of hybridization were reduced in the DNA from the amicronucleate cells relative to DNA from a wild-type cell line, indicating that less than one micronucleus equivalent of the micronucleus-specific DNA sequences was retained in the amicronucleate cell line. Thus many micronucleus-specific DNA sequences were eliminated from the developing macronucleus of BI3840 as they are in wild-type cells, but in at least two cases the elimination was incomplete. In situ hybridization suggested that the DNA sequences which are limited to the micronucleus in wild-type cells are present in the macronucleus of the amicronucleate cell line. Southern blots of DNA from the amicronucleate cell line were also probed with DNA sequences which are retained in the macronucleus. At least two types of genome rearrangements occurred in the BI3840 macronucleus as they do in wild-type cells. No spurious rearrangements were observed

Physical maps of 4p16.3, the area expected to contain the Huntington disease mutation

The gene for Huntington disease, a neurodegenerative disorder with autosomal dominant inheritance, has been localized to the terminal portion of the short arm of human chromosome 4 (4p16.3) by linkage analysis. Since eventual isolation of the gene requires the application of high-resolution genetic analysis coupled with long-range DNA mapping and cloning techniques, we have constructed a physical map of the chromosomal region 4p16.3 using more than 20 independently derived probes. We have grouped these markers into three clusters which have been ordered and oriented by genetic and somatic cell genetic mapping information. The mapped region extends from D4S10 (G8) toward the telomere and covers minimally 5 Mb.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28761/3/0000591.pd

Increased recombination adjacent to the Huntington disease-linked D4S10 marker

Huntington disease (HD) is caused by a genetic defect distal to the anonymous DNA marker D4S10 in the terminal cytogenetic subband of the short arm of chromosome 4 (4p16.3). The effort to identify new markers linked to HD has concentrated on the use of somatic cell hybrid panels that split 4p16.3 into proximal and distal portions. Here we report two new polymorphic markers in the proximal portion of 4p16.3, distal to D4S10. Both loci, D4S126 and D4S127, are defined by cosmids isolated from a library enriched for sequences in the 4pter-4p15.1 region. Physical mapping by pulsed-field gel electrophoresis places D4S126 200 kb telomeric to D4S10, while D4S127 is located near the more distal marker D4S95. Typing of a reference pedigree for D4S126 and D4S127 and for the recently described VNTR marker D4S125 has firmly placed these loci on the existing linkage map of 4p16.3. This genetic analysis has revealed that the region immediately distal to D4S10 shows a dramatically higher rate of recombination than would be expected based on its physical size. D4S10-D4S126-D4S125 span 3.5 cM, but only 300-400 kb of DNA. Consequently, this small region accounts for most of the reported genetic distance between D4S10 and HD. By contrast, it was not possible to connect D4S127 to D4S125 by physical mapping, although they are only 0.3 cM apart. A more detailed analysis of recombination sites within the immediate vicinity of D4S10 could potentially reveal the molecular basis for this phenomenon; however, it is clear that the rate of recombination is not continuously increased with progress toward the telomere of 4p.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29546/1/0000634.pd