Search PubMed⌕ Search

Biomedical subjects

A Kahn

Publications and source records attributed to A Kahn.

At least 307 records · Page 17Linked to original sources
PubMed1990

Dystrophin gene transcribed from different promoters in neuronal and glial cells.

It has been shown that the dystrophin gene, which is defective in patients with Duchenne and Becker muscular dystrophy (reviewed in ref. 1), is transcribed in brain from a specific promoter that is different from the one used in muscle, and so the two types of transcripts differ at least in their first exon. We recently found that the dystrophin gene is expressed at a higher level in primary cultures of neuronal cells than in astro-glial cells derived from adult mouse brain. Here we investigate the use of two different promoters in each cell type. Our results demonstrate that the brain-type promoter of the dystrophin gene is highly specific to neurons, in which there is a significant increase in the amount of brain-specific messenger RNA during the course of in vitro maturation. By contrast, the muscle-type promoter is active in a wider range of cell types, including not only striated and smooth muscle, but also glial cells to a lesser extent, and probably neurons.

Animals↗
PubMed1990

Quantitative estimation of minor mRNAs by cDNA-polymerase chain reaction. Application to dystrophin mRNA in cultured myogenic and brain cells.

Amplification of the mRNA polymerase chain reaction is a very sensitive technique to detect low-abundance transcripts. We describe in this paper conditions necessary to make this technique quantitative. Quantification is performed in the exponential phase of the amplification process and the results are standardized with respect to those obtained with an exogenous mRNA which is co-reverse-transcribed and co-amplified in the same reaction as the analyzed transcripts. The primers are chosen in different exons to distinguish the amplification of mRNA fragments from the amplification of contaminating DNA. Analysis of the kinetics of amplification and parameters influencing this kinetics shows that: (a) in the exponential phase of amplification, the amount of amplified fragments is proportional to the initial amount of transcripts; (b) in a certain range of length fragment, the yield of amplification is inversely proportional to the length of the amplified fragments. Using this method we have demonstrated that the dystrophin gene is already activated at the myoblastic stage. A quantitative estimation of the transcript showed that the expression of this gene increases strongly in the course of in vitro myogenesis. In primary culture of mouse brain cells, the dystrophin gene was found to be more expressed in neuronal than in glial cells.

Animals↗
PubMed1990

Mapping of normal brain maturation in infants on phase-sensitive inversion--recovery MR images.

It is illustrated that phase-sensitive inversion-recovery MR images are particularly well suited for the monitoring of brain maturation and myelination in the neonate and young infant. Provided appropriate timings are applied with the inversion-recovery MR pulse sequence, the myelinated areas show up as bright spots in the phase-sensitive images. The chronology of the appearance, and the location of these hyperintense zones correlate well with the chronology of brain maturation, as assessed by other means. In particular, the progressive functional capabilities of the infant correlate well with the progress of myelination, as exhibited by the MR images.

Brain↗
PubMed1990

Prospective study on the prevalence of sudden infant death and possible risk factors in Brussels: preliminary results (1987-1988).

A prospective study was carried out to assess the frequency of sudden infant death (SID) in the Brussels area. The study was conducted between January and December 1987 on infants presented to the health clinics of the Brussels "Office de la Naissance et de l'Enfance" (ONE). The infants entered the study if: (a) they were born between January 1 and December 31, 1987; (b) they attended an ONE consultation in the Brussels area between January 1987 and December 1988; (c) visits were repeated monthly during the first 12 months of life, or until death occurred; and (d) standard questionnaires were completed for each visit. For 4,064 infants these four criteria were fulfilled. During the study period 7 infants died of SID. Their deaths were unexpected and remained unexplained despite post-mortem investigations. For each SID case, 10 control infants were selected from the same health clinics. Controls matched the SID cases in the following respects: (a) dates of visits; (b) sex; (c) gestational age; (d) legal age; and (e) the profession of both parents. For most of the 65 items studied no significant difference was seen between the 7 SID infants and their 70 matched controls. Only two variables significantly differentiated the two groups. Repeated fatigue during feeding was seen in 4 of the 7 SID cases, but only in 10 of the 70 control infants (Fisher P = 0.017). Profuse sweating during sleep was reported in 2 of the 7 SID infants, and in none of the 70 controls (Fischer P = 0.007). These two infants' bedclothes were repeatedly wet with sweat.(ABSTRACT TRUNCATED AT 250 WORDS)

Belgium↗
PubMed1990

Home monitors for infants: use, misuse, and "over-the-counter" use.

The prevalence of "over-the-counter" monitors, was surveyed in infants referred to five Belgian paediatric centres between September 1987 and March 1988 for evaluation of their risk for sudden infant death (SID). Questionnaires were collected from 1625 families. Of the infants, 8.9% were already being monitored at home. For 78.1% of the infants no medical advice had been solicited, and for 21.9%, a paediatrician or a general practitioner had advised home monitoring without previous evaluation. Forty of 824 infants referred with no history of SID, and no history of apparent life-threatening event (ALTE), were monitored (4.8%). Monitoring was started for 3.8% (5 out of 130) of the infants who had lost a cousin or an uncle to SID, and for 22.2% (69 of 310) of the younger siblings of a SID victim. Of the 341 infants who had presented with an ALTE, monitoring was started in 32 (9.4%). The infants were monitored with respiratory monitors only, and in 86% of the monitors, the alarm delay had been regulated unnecessarily low.

Belgium↗
PubMed1990

Recent advances in sudden infant death syndrome: possible autonomic dysfunction of the airways in infants at risk.

Epidemiological studies of sudden infant death syndrome (SIDS) reveal a progressive increase in the incidence of cases, suggesting that the in utero environment and postneonatal care were less than optimal. Subtle differences in symptoms could indicate that, since birth, the SIDS infants are different from control infants, some having an autonomic dysfunction of the airway controls. These observations could contribute to a better understanding of some of the causes of sudden death in infants and could eventually lead to new therapeutic approaches.

Autonomic Nervous System↗
PubMed1990

Brief airway obstructions during sleep in infants with breath-holding spells.

We investigated the possibility that infants with breath-holding spells have breathing disorders during sleep. Seventy-one breath holders with a median age of 14 weeks were selected from a well babies clinic because of their histories: 34 infants without loss of consciousness, and 37 with loss of consciousness (21 of the latter had had cyanotic spells, 14 pallid spells, and 2 combined cyanotic and pallid spells). For each breath holder, one control infant without a history of breath holding was chosen from the same clinic. All infants were healthy and had no known cause of disrupted breathing during sleep. Their histories indicated that the breath holders were covered with sweat during sleep (p = 0.005) or wakefulness (p = 0.006) significantly more often than were the control infants. The infants were studied during a one-night monitoring session, and the 142 sleep recordings were analyzed without knowledge of the history. The breath holders had significantly less nonrapid eye movement (stage III) sleep, more indeterminate sleep, more arousals, and more sleep-stage changes than the control infants had. Central apneas were evenly distributed in the two groups. Airway obstructions were found in 41 breath holders and six control infants; the obstruction lasted longer in the breath holders. The infants with airway obstruction during sleep snored more often (p = 0.023) and sweated more (p = 0.035) during sleep. The water evaporation rate, measured on the forehead with an evaporation meter, was significantly greater in the breath holders (p = 0.001). Ocular compression induced longer asystoles in the infants with pallid syncopes than in either those with cyanotic syncopes (p = 0.036) or those without loss of consciousness (p = 0.031). We conclude that the obstructed breathing during both wakefulness and sleep could be related to a common immature breathing control.

Female↗
PubMed1990

Sleep apneas and acid esophageal reflux in control infants and in infants with an apparent life-threatening event.

Clinical experience shows that episodes of apnea can occur during regurgitations or vomiting. We questioned whether sleep apneas could be related temporally to documented falls in esophageal pH, when no clinical symptoms of emesis are witnessed. Twenty infants admitted after an apparently life-threatening event ('ALTE') during sleep, but with no clinical symptoms of vomiting or regurgitations at the time of the event, and ten control infants were studied. All infants had occasional episodes of regurgitations. Polygraphic monitoring of state of alertness, cardiorespiratory activity and low esophageal pH was performed continuously during 1 night. The data were analyzed blindly. A total of 334 central and 36 obstructive apneas were monitored, mainly in the ALTE group, during NREM sleep. A total of 116 falls in esophageal pH below 4 units were seen in 18 infants; 50% occurred during wakefulness, and 31% in REM sleep. Arousals or body movements preceded the pH fall in 50% of the cases. Within 5 min following the reflux onset, 18 central apneas (7.2% of the apneas) were seen. There was no correlation between the duration, or the lowest values of esophageal pH measured, and the number or duration of apneas. No obstructive apnea, bradycardia or arousal followed the falls in esophageal pH. Acid esophageal reflux did not play a significant role in the development of apnea in our population.

Esophagus↗
PubMed1990

Pituitary-like proopiomelanocortin transcripts in human Leydig cell tumors.

Proopiomelanocortin is a polypeptide precursor molecule, the processing of which generates ACTH, beta-endorphin, the beta- and gamma-lipotropins, the joining peptide, and the NH2-terminal fragment. Anterior pituitary corticotrophs are the major site of proopiomelanocortin gene expression in man and the predominant, if not sole source of circulating ACTH. Recent data have established that proopiomelanocortin gene expression also occurs in various normal nonpituitary tissues, one of the best studied being the testis. In this latter organ the dominant gene products are short transcripts of approximately 800 nucleotides, which lack the first two exons of the gene and cannot encode a complete proopiomelanocortin molecule. In this report we show that the mode of proopiomelanocortin gene expression is occasionally modified in human Leydig cell tumors: a 1,200-nucleotide mRNA species identical to that in the pituitary is produced. It results from the usual (pituitary) start site of transcription and thus can encode the complete proopiomelanocortin molecule. In two out of six tumors, large amounts of the 1,200-nucleotide transcript led to a dramatic increase of approximately 1,000-fold in proopiomelanocortin peptide concentrations as compared with the normal and peritumoral testis. Proopiomelanocortin processing in these tumors generates various peptide fragments including ACTH. These results may help to understand the mechanism of proopiomelanocortin expression in nonpituitary tumors and have implications for the more general phenomenon of ectopic hormone secretion.

Blotting, Northern↗
PubMed1990

Expression of the gene for anti-Müllerian hormone.

The expression of anti-Müllerian hormone, also called Müllerian-inhibiting substance or factor, is limited to immature Sertoli and post-natal granulosa cells. To gain information on the genetic mechanisms of this tissue- and development-specific regulation, a human genomic clone containing 3.6 kilobases of 5' flanking sequences has been isolated and sequenced. Transcription initiation sites include a major site, at the same position as in the bovine gene, and 3 minor sites, accounting together for 12% of transcripts. Sequences of potential interest include an Sp1 binding site, minisatellite-like regions, and a 13-base pair palindrome, nearly identical to the oestrogen response element of the vitellogenin genes. This palindrome binds to the human oestrogen receptor in vitro and activates transcription of a hybrid gene when several copies are inserted 5' of a thymidine kinase promoter. Further studies are needed to determine whether this palindrome is implicated in a feed-back loop regulating oestrogen synthesis in granulosa cells.

Anti-Mullerian Hormone↗
PubMed1990

The red-green visual pigment gene region in adrenoleukodystrophy.

Although recent data established that a specific very-long-chain fatty acyl-CoA synthetase is defective in X-linked adrenoleukodystrophy (ALD), the ALD gene is still unidentified. The ALD locus has been mapped to Xq28, like the red and green color pigment genes. Abnormal color vision has been observed in 12 of 27 patients with adrenomyeloneuropathy (AMN), a milder form of ALD. Furthermore, rearrangements of the color vision gene cluster were found in four of eight ALD kindreds. This led us to propose that a single DNA rearrangement could underlie both ALD and abnormal color vision in these patients. Study of 34 French ALD patients failed to reveal a higher than expected frequency of green/red visual pigment rearrangements 3' to the red/green color vision gene complex. The previous report of such rearrangements was based on small numbers and lack of knowledge that the frequency of "abnormal" color vision arrays on molecular analysis was twice as high as expected on the basis of the frequency of phenotypic color vision defects. The red/green color pigment (R/GCP) region was studied by pulsed-field gel electrophoresis in 14 of these patients, and we did not find any fragment size difference between the patients and normal individuals who have the same number of pigment genes. The R/GCP region was also analyzed in 29 French and seven North American ALD patients by using six genomic DNA probes, isolated from a cosmid walk, that flank the color vision genes. No deletions were found with probes that lie 3' of the green pigment genes. One of the eight previously reported ALD individuals has a long deletion 5' of the red pigment gene, a deletion causing blue cone monochromacy. This finding and the previous findings of a 45% frequency of phenotypic color vision defects in patients with AMN may suggest that the ALD/AMN gene lies 5' to the red pigment gene and that the frequent phenotypic color vision anomalies owe their origin to deleted DNA that includes regulatory genes for color vision. It is possible, however, that phenotypic color vision anomalies in AMN may be phenocopies secondary to retinal or neural involvement by the disease. The single case of blue cone monochromacy may therefore be a fortuitous coincidence of two diseases.

Adrenoleukodystrophy↗
PubMed1989

Expression of the rat L-type pyruvate kinase gene from its dual erythroid- and liver-specific promoter in transgenic mice.

The gene for the L-type pyruvate kinase possesses two promoters which are located 500 base pairs apart. The L promoter is specific to liver and regulated by hormones and diet; the L' promoter is specific to erythroid cells. We produced two series of transgenic mice carrying either the entire rat L-pyruvate kinase gene or a minigene devoid of exons two to nine, with 2.7 kilobases of flanking sequences 5' to the cap site of the L' promoter and 1.4 kilobases 3' to the downstream polyadenylation site. In both series the patterns of expression from the two promoters were similar to those of the endogenous rat gene. The rat L promoter was expressed strongly in liver and weakly in kidney and gut of adult transgenic mice. Moreover, it was regulated like the endogenous rat L-pyruvate kinase gene upon hormonal and nutritional adaptation: the level of L-pyruvate kinase mRNA was decreased dramatically by 24 h of starvation, while refeeding a carbohydrate-rich diet strongly stimulated expression of the transgenes. This stimulation was prevented by glucagon. Use of alternative polyadenylation sites in the last exon of the rat L-type pyruvate kinase gene was similar for both types of transgenes and similar to that in rat and not control mice, suggesting that the transgenes contain the sequences that control the choice of polyadenylation site. Transcription of the minigene was higher than that of the entire transgene, probably due to the high copy number of the minigene. At the protein level, rat L subunits encoded by the entire transgene were more abundant than mouse subunits in the liver of adult transgenic mice. In contrast, expression of the rat L' promoter in fetal liver was only 5% of that in fetal rat liver, and we were unable to detect rat L' subunits of pyruvate kinase enzyme in the red blood cells from transgenic mice. Our results suggest that the integrated DNA contains all elements necessary for tissue specificity (L' and L) as well as hormonal and nutritional control (L) of expression of the rat transgene. Nevertheless, a L'-specific activating element may be missing.

Animals↗
PubMed1989

Proteins binding to the liver-specific pyruvate kinase gene promoter. A unique combination of known factors.

A 183 base-pair fragment of the liver-specific promoter of the L-type puruvate kinase (L-PK) gene has been shown by transfection assay to be sufficient to confer a tissue-specific expression to a reporter gene. The proteins binding in vitro to this fragment have been investigated by a combination of DNase I footprinting, gel retardation of synthetic oligonucleotides and ultraviolet cross-linking. Four proteins from liver nuclear extracts bind to the investigated fragment. They were called, from 3' to 5', L1 to L4 binding factors. The L1 site (nucleotides -95 to -66 with respect to the cap site) binds hepatocyte nuclear factor 1 (HNF1), a liver-specific protein. The L2 site (nucleotides -114 to -97) binds the ubiquitous nuclear factor 1 (NF1), or a related factor. The L3 site (nucleotides -144 to -126) binds liver factor A1 (LF-A1), another liver-specific protein. Finally, the L4 site (nucleotides -168 to -145) binds major late transcription factor (MLTF/USF/UEF), an ubiquitous protein. Each of these proteins has been detected in other liver-specific promoters, but their combination is unique to the liver-specific promoter of the L-PK gene.

Animals↗
PubMed1989

Regulation of the expression of the L-type pyruvate kinase gene in adult rat hepatocytes in primary culture.

Hepatocytes isolated from adult fasted rats and cultured in the presence of thyroid hormones, glucocorticoids, and in a serum-free medium conserve the essentials of their differentiated function and hormonal sensitivity for at least 1 week. In these cells, the gene for L-type pyruvate kinase is expressed only when glucose and insulin are present together, each of them being inactive by itself. Inhibition of the expression of the L-type pyruvate kinase gene which occurs when glucose and/or insulin are removed from the culture medium is not associated with accumulation of the phosphoenolpyruvate carboxykinase mRNA, which argues against the involvement of intracellular cyclic AMP in this phenomenon. Rather, a transcriptional activator, derived from carbohydrate metabolism and accumulating in the presence of insulin, seems to be needed to support the expression of the L-type pyruvate kinase gene. Glucagon, in vitro as in vivo, inhibits production of the L-type pyruvate kinase mRNAs. In addition to their roles on the production of these mRNAs, glucose and insulin on the one hand and glucagon on the other have profound effects on the stability of the L-type pyruvate kinase messengers: the half-life of the mRNA whose production has been blocked by actinomycin D is 1 h in the presence of glucagon and 24 h in the presence of glucose and insulin. Glucagon and glucose/insulin partially antagonize each other's effect on mRNA stability.

Animals↗