Gene targeting in embryonic stem cells.
Explore the source record for details and available documents.
Animals↗
Biomedical subjects
A C Davis
Publications and source records attributed to A C Davis.
A null c-myc mutation causes lethality before 10.5 days of gestation in homozygotes and reduced fertility in heterozygous female mice.
To directly assess c-myc function in cellular proliferation, differentiation, and embryogenesis, we have used homologous recombination in embryonic stem cells to generate both heterozygous and homozygous c-myc mutant ES cell lines. The mutation is a null allele at the protein level. Mouse chimeras from seven heterozygous cell lines transmitted the mutant allele to their offspring. The analysis of embryos from two clones has shown that the mutation is lethal in homozygotes between 9.5 and 10.5 days of gestation. The embryos are generally smaller and retarded in development compared with their littermates. Pathologic abnormalities include the heart, pericardium, neural tube, and delay or failure in turning of the embryo. Heterozygous females have reduced fertility owing to embryonic resorption before 9.5 days of gestation in 14% of implanted embryos. c-Myc protein is necessary for embryonic survival beyond 10.5 days of gestation; however, it appears to be dispensable for cell division both in ES cell lines and in the embryo before that time.
Alleles↗
Epidemiology of bacterial meningitis.
This 10 year retrospective study of all causes of bacterial meningitis for children resident in Nottingham District Health Authority area reports an annual incidence rate per 100,000 children aged 0-16 years of 16.0 (95% confidence interval 14.0 to 18.1). There was a steady increase in incidence from 9.6/100,000 in 1980 to 24.3/100,000 in 1989. This was mainly due to an increase in the incidence of meningococcal infections in the age group 1 month to 5 years. Incidence rates varied with age being: 37.2/100,000 (25.9 to 53.5) for 0-28 days of age, 115.5/100,000 (93.9 to 141.9) for 1-11 months of age, 28.5/100,000 (23.1 to 35.3) for 12-59 months of age, and 2.8/100,000 (1.9 to 4.1) for 5-16 years of age. Overall annual mortality incidence per 100,000 was 1.8 (1.2 to 2.8). For the different age groups this was: 10.1 (4.8 to 21.1) for 0-28 days, 11.5 (6.0 to 22.2) for 1-11 months, 1.0 (0.3 to 3.1) for 12-59 months, and 0.4 (0.1 to 1.2) for 5-16 years of age. There were interactions between the type of meningitis and the year of the infection on the mortality rate. Mortality decreased in those with infections caused by bacteria other than Neisseria meningitidis and Haemophilus influenzae.
Adolescent↗
Investigation of coelectroporation as a method for introducing small mutations into embryonic stem cells.
We have investigated coelectroporation as a method for introducing minor genetic changes into specific genes in embryonic stem cells. A selectable marker (neo) and a targeting replacement vector designed to insert a 4-bp insertion into exon 3 of the mouse hypoxanthine-guanine phosphoribosyltransferase (HPRT) gene were coelectroporated into embryonic stem cells and selected in G418 and 6-thioguanine (6-TG). HPRT-negative clones were obtained at a frequency of approximately 1 per 520 G418r clones. Southern analysis and the polymerase chain reaction were used to demonstrate that 3 of 36 of the 6-TG-resistant clones had the desired 4-bp insertion without any other disruption of the HPRT locus. Initial studies indicated that the other 33 6-TG-resistant clones probably resulted from the targeted integration of a concatemer containing both the targeting construct and the selectable neo gene.
Blotting, Southern↗
The effects of hearing loss and age of intervention on some language metrics in young hearing-impaired children.
This study examined the oral language production abilities of a group of young children with bilateral sensorineural hearing impairments (greater than 25 dB HL). The effects of age of intervention-as indexed by age of detection, referral, first appointment and hearing-aid fitting-and of the severity of their hearing impairments on spoken language and communication were the foci of the study. Children were aged between 27 and 80 months with hearing threshold levels ranging from 32 to 98 dB in the better ear. All were audio- and video-taped in their own homes, in an unstructured play setting with the mother. Measures of expressive language ability were extracted including mean length of utterance, vocabulary size, words per min., total utterance attempts per min., proportion of non-verbal utterances and the proportion of questions asked by the child. No significant correlations were found between the children's hearing impairments and their scores on the language measures once age at interview had been statistically controlled. However, significant correlations were found between the language measures and the ages at which the children received intervention for their hearing impairments, in particular for vocabulary and those language measures denoting the rate and quality of the child's interaction during the episode recorded. This finding is consistent with some of the arguments to be found in the small body of data addressing the question of early intervention.
Age Factors↗
AP17 and AP19, the mammalian small chains of the clathrin-associated protein complexes show homology to Yap17p, their putative homolog in yeast.
AP17 and AP19 are the smallest polypeptide chain components of AP-2 and AP-1, the clathrin-associated protein complexes found in coated structures of the plasma membrane and Golgi apparatus of mammalian cells. cDNA clones representing the entire coding sequence of AP17 and AP19 were isolated from rat and mouse brain cDNA libraries, respectively. Determination of their nucleotide sequence predicts proteins of 142 and 158 amino acids with Mr 17,018 and 18,733. A sequence comparison of rat brain AP17 with mouse brain AP19 demonstrates that the small chains are highly related. A computer search for other related proteins has uncovered in yeast a previously unknown gene whose DNA sequence encodes a protein homologous to the small chain of AP complexes. The yeast sequence predicts Yap17p, a protein with 147 amino acids and a Mr of 17,373 that is slightly more related to the mammalian AP17 chain than to its AP19 counterpart.
Adaptor Protein Complex 1↗
Early detection of hearing impairment: what role is there for behavioural methods in the neonatal period?
A survey of the use of behavioural methods for neonatal hearing screening in 1985 (1) concluded that the future for automated methods was quite promising. Since then several studies have assessed the two main automated behavioural tests: the Auditory Response Cradle (ARC) and the Crib-o-Gram (COG). As a screen targeted at neonatal intensive care unit (NICU) babies and other high risk groups (at present the most cost-effective form of neonatal hearing screening), the ARC is shown to have low sensitivity, even for severe hearing impairments, and the COG has an unacceptably low specificity. Any future for behavioural testing during this period must therefore rely on new implementations flowing out of a fundamental understanding of (a) the way in which neonates respond to sound and (b) the ways in which a behavioural test might complement screening with Auditory Brainstem Responses (ABR) or Evoked Oto-acoustic Emissions (EOAE). A clearer understanding of the relative benefits of detecting different degrees of hearing impairment at birth in both the NICU population and the unrestricted population is urgently needed. To determine what role should be played by specific screening programmes such benefits need to be balanced against the total costs of screening assessment and rehabilitation, in which false positives (low specificity) play a large part.
Acoustic Stimulation↗
Dental disease prevalence in Alabama school-aged children.
Explore the source record for details and available documents.
Adolescent↗
Hearing disability in people aged 50-65: effectiveness and acceptability of rehabilitative intervention.
OBJECTIVE: To determine the best means of detecting hearing disability in subjects aged 50-65 and whether rehabilitative intervention is acceptable in this age group. DESIGN: Questionnaire survey of patients on general practice age-sex registers. Two types of questionnaire were used, one being based on the closed set approach of the Institute of Hearing Research questionnaire, which had been used in a pilot study, and the other being a simplified version of this questionnaire developed by the Welsh Hearing Institute and based on open set questions. Questionnaires were sent up to three times, and any patients who had not responded two months after the last posting were personally contacted. SETTING: Two general practices in Glyncorrwg and Blaengwynfi in the Afan valley, West Glamorgan. PATIENTS: 271 Patients in Glyncorrwg (136 men, 135 women) and 333 patients in Blaengwynfi (173 men, 160 women) aged 50-65. INTERVENTIONS: All patients indicating hearing disability in answering the questionnaires were invited to attend for a evaluative session in their village. After audiometric testing advice and arrangements for fitting a hearing aid were offered as appropriate. MAIN OUTCOME MEASURES: Response rates and prevalence of hearing disability before intervention and of possession of hearing aids before and after intervention. RESULTS: After three postings and personal contact the response rate was 98% (266/271) in Glyncorrwg, where the complex questionnaire was used, and 97% (322/333) in Blaengwynfi. The prevalence of hearing disability was respectively 53% (141/266) and 46% (148/322) and the prevalence of owning a hearing aid 7% (19/266) and 8% (24/322). After intervention the possession of hearing aids rose to 24% (64/266) in Glyncorrwg and 22% (71/322) in Blaengwynfi; six months later the aids were being used regularly. A direct comparison of the two questionnaires in 69 subjects from Blaengwynfi showed no significant differences in the amount of disability detected by each one. The first posting of questionnaires detected 65% (189/289) of the hearing disability in the two villages or 78% (72/92) of those prepared to accept hearing aids for the first time; 96% (88/92) of those who accepted hearing aids were detected by two postings. CONCLUSIONS: Simple questionnaires are effective in detecting hearing disabilities in people aged 50-65, and intervention was acceptable in many of those who reported having difficulties in hearing. The response rates from successive postings suggest that two postings are sufficient in terms of the return in detecting those who will accept intervention.
Aged↗
Longitudinal study of hearing.
Our knowledge of the progression and aetiology of hearing impairments is mainly inferred from cross-sectional studies of populations or individual case studies of relatively rare conditions. Longitudinal studies of carefully stratified samples enable scientific analysis of these two aspects of the ageing auditory system and also provide much needed incidence data on the basis of which to plan comprehensive hearing services. This preliminary paper using data from two studies over relatively short periods (between 2-4.5 years in Great Britain (GB) and up to 8 years in Denmark (DK] confirms (a) that deterioration of hearing impairment appears to be continuous and gradual for the majority (up to 97% on a 2-year assessment) with a median of about 5-6 dB/decade, and (b) that for mid-frequency average hearing levels applied to the samples of average age 55 (range 40-65) the incidence of hearing impairment is predicted accurately by interpolation of the relevant prevalence figures, and runs at about 1.8% per annum for 25+ dBHL bilateral hearing impairments. However, the actual rate of deterioration does seem to be influenced by age, those over 55 showing a high rate of up to 9 dB/decade against 3 dB/decade for those under 55. This implies that study over a much longer time is required to find a more exact form for the relationship between age and the rate of deterioration of hearing impairments.
Adult↗
Epidemiological profile of hearing impairments: the scale and nature of the problem with special reference to the elderly.
The nature and scale of services for hearing-impaired people should be formed in the light of the demographic profile of the hearing-impaired. This paper furnishes data for three elements of that profile: the number of hearing-impaired people in England and Wales, the increase in the number of hearing-impaired that might be expected given the growth of the elderly population in England and Wales, and the major factors that influence use of hearing services at present. The combination of reliable prevalence data (1) with demographic information (2) gives good estimates of the numbers of hearing-impaired people and their age distribution. Thus an estimate of 7.4 million people with average hearing thresholds at mid frequencies of 25+ dBHL can be made for an adult population of 38.7 million (aged 18+ years). Eighty percent of these hearing-impaired people are aged over 60 years. Given no change in prevalence rates over the next 20 years, the demographic structure of England and Wales will increase the number of hearing-impaired by approximately 20%. The detailed form of service for the elderly will need to take into account factors shown to put groups at a disadvantage. In particular, the large shortfall in services for the very elderly (over 80 years) and those in manual occupations needs to be addressed.
Adult↗
Mutations of the mouse mu H chain which prevent polymer assembly.
Earlier work has shown that truncated mu-chains lacking the carboxy-terminal C mu 4-tail region are secreted as monomeric rather than polymeric IgM and that the monomer phenotype is not due to the lack of a disulfide bond at Cys-575 in the tail. In order to define with greater precision, the molecular requirements for IgM polymer assembly, we have isolated several mutant hybridomas which produce monomeric IgM. For three such mutants, we synthesized cDNA clones of their mu mRNA and identified a mutation in the mu-chain which was responsible for the failure to assemble polymers. Mutant 205 has a 2-bp deletion which results in a termination codon after amino acid 556, effectively deleting the last 20 amino acids of the mu-chain. In conjunction with earlier reports, this result shows that the tail plays some role in assembly other than providing Cys-575, the penultimate amino acid, for disulfide bond formation. Both mutant 21 and mutant 201 have an A to G transition, which results in Tyr-455 in the fourth constant domain being replaced by a cysteine. We conclude that the integrity of both the C mu 4 domain and the 19 amino acid tail are required for the mu H chain to be assembled into polymeric IgM.
Amino Acid Sequence↗
Organization and structure of the Qa genes of the major histocompatibility complex of the C3H mouse: implications for Qa function and class I evolution.
We have determined the structure and organization of the entire Qa family of class I genes from the major histocompatibility complex of the C3H mouse. Restriction maps of overlapping lambda and cosmid clones reveal that there are only five Qak genes: Q1k, Q2k, Q4k, Q10k and a Q5/9 hybrid, presumably generated by unequal homologous recombination. The resulting deletion of Q6-Q9 is consistent with the Qa-2null phenotype of this mouse strain. We have sequenced the Qak genes, and predict that each may encode a class I molecule with a structure comparable with that proposed for the transplantation antigens. Furthermore, these Qa products should be able to bind peptides and interact with appropriate T-cell receptors. Interestingly, in comparing Qak and H-2k sequences, we find limited evidence of interlocus gene conversion between Qa and H-2 loci, suggesting that the Qa genes are not likely to serve as a reservoir of genetic information for the generation of H-2 diversity within this haplotype.
Amino Acid Sequence↗
Intermolecular disulfide bonding in IgM: effects of replacing cysteine residues in the mu heavy chain.
The conventional model of polymeric IgM depicts a unique structure in which the mu heavy chains and J chain are joined by well defined disulfide bonds involving cysteine residues at positions 337, 414 and 575 of the mu chain. To test this model, we have used site directed mutagenesis to produce IgM in which these cysteines have been replaced by serine. In each case the single mutants were able to assemble polymeric IgM, which was analyzed for its size, morphology, J chain content and activity in complement dependent cytolysis. Whereas normal polymeric IgM is composed predominantly of pentameric and hexameric molecules, the mutant IgM-Ser414 is covalently assembled as pentamers and smaller forms; IgM-Ser575 is assembled as covalent hexamers. IgM-Ser337 appears to include the same pentameric and hexameric forms as normal IgM except that, unlike normal polymeric IgM, most pentameric/hexameric IgM-Ser337 is not covalently assembled. J chain is present in polymeric IgM-Ser337 but absent in polymeric IgM-Ser414 and IgM-Ser575. IgM-Ser414 is defective in activating the classical pathway of complement dependent cytolysis. Our observations are consistent with models in which the covalent linkages between mu chains are mediated by disulfide bonded Cys337-Cys337, Cys414-Cys414 and Cys575-Cys575 but indicate that the arrangement of these Cys-Cys pairs in series and in parallel varies among and within IgM molecules.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Sequence analysis of the C3H H-2K1k gene: relationship to the H-2 loci.
Explore the source record for details and available documents.
Amino Acid Sequence↗
Differential glycosylation of polymeric and monomeric IgM.
A small fraction of normal IgM is secreted as monomers rather than polymers. We show here that the mu chains of monomeric IgM are glycosylated differently from the mu chains of polymeric IgM and are comparable in their glycosylation to the mu chains from mutant hybridoma cell lines which produce predominantly monomeric IgM. The difference in glycosylation between monomer and polymer mu chains is due to differences in the terminal processing of their oligosaccharides. The glycosylation of the mutant mu chains is not itself responsible for the block in IgM polymer formation.
1-Deoxynojirimycin↗
IgM--molecular requirements for its assembly and function.
The conventional model of IgM structure depicts a unique, array of mu, L and J chains, held together by well-defined disulfide bonds and other interactions. Some, but not all, recent data support this model. Here Ann Davis and Marc Shulman review recent, as well as older, studies of IgM and consider their implications for our understanding of IgM structure and function.
Animals↗
The prevalence of hearing impairment and reported hearing disability among adults in Great Britain.
Estimates for the prevalence of self-reported hearing disability and measured hearing impairment as a function of age in the adult population of Great Britain (GB) are reported from two 2-stage surveys. The main study was conducted in Cardiff, Glasgow, Nottingham and Southampton, with rigorous audiological assessment at the second stage. A supplementary study used a sample representative of GB with simplified domiciliary audiological assessments. In the main study, neither stage showed any gross bias arising from the particular cities chosen; the estimates from the first stage are free of bias arising from non-response. The estimates from the second stage are relatively free of bias arising from non-attendance. For the present purposes, defining a 'significant' level of hearing impairment as at least 25 dBHL averaged over the frequencies 0.5, 1, 2, 4 kHz, 16% of the adult population (17-80 years) have a bilateral, and about one in four a unilateral or bilateral, hearing impairment. About 10% of the adult population (aged 17+) report bilateral hearing difficulty in a quiet environment.
Adult↗