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Biomedical subjects

M Ohresser

Publications and source records attributed to M Ohresser.

18 recordsLinked to original sources
PubMed1997

Expression of the arylsulphatase reporter gene under the control of the nit1 promoter in Chlamydomonas reinhardtii.

In Chlamydomonas reinhardtii, the expression of the nit1 gene encoding nitrate reductase is dependent on the nature of the nitrogen source and on other environmental factors. We have fused the nit1 promoter region to the arylsulphatase (ars) reporter gene lacking its own promoter and introduced this chimeric construction (nit1/ars) into a wall-less strain of C. reinhardtii. A new and sensitive method, based on the use of alpha-naphthylsulphate as a substrate and a diazonium salt as a chromogenic post-coupling agent, was developed to detect the activity of arylsulphatase (an enzyme which is almost completely secreted in the culture medium) both in vitro and in agar plates. The transformants carrying nit1/ars did not express arylsulphatase when grown in ammonium-sufficient medium but readily accumulated the enzyme in ammonium-free medium either supplemented, or not supplemented, with nitrate or nitrite. The nit1/ars construct, however, was not expressed in the nit2 mutant lacking a specific transcription regulator controlling the expression of nit1. These results, together with the observation that the transcription of nit1/ars is initiated at the same sites as the nit1 endogenous gene, confirms the hypothesis that the regulation of nit1 expression takes place mainly at the transcriptional level. The expression of the ars gene from the nit1 promoter was high enough to allow direct measurements of arylsulphatase activities in pools of transformants without prior isolation of nit1/ars clones. This original procedure has permitted the analysis of the effects of nested deletions in the nit1 promoter region on the expression of the reporter gene. The results indicate that the -282 to -198 sequence is required for transcription to occur and that the -751 to -282 region contains several elements mediating nit1 expression.

Animals↗
PubMed1997

Intron-length polymorphism at the actin gene locus mac-1: a genetic marker for population studies in the marine mussels Mytilus galloprovincialis Lmk. and M. edulis L.

A novel intron-length polymorphism at the actin gene locus mac-1 is here reported and used as a genetic marker for population studies in mussels of the genus Mytilus. Two closely related genes subsequently identified as alleles, mac-1a1 and mac-1b1, from a genomic library of M. galloprovincialis were partially cloned and sequenced. They mainly differed from each other by a 65-bp insertion within their first intron. Polymerase chain reaction (PCR) primers were designed outside the insertion. The PCR analysis of 166 individual mussels from M. galloprovincialis and M. edulis populations revealed three size-classes of alleles or allelomorphs, two of which were of the expected sizes for mac1a1 and mac-1b1. One allelomorph was absent from M. edulis samples, although it was present at substantial frequencies in M. galloprovincialis populations. The frequencies of the two other allelomorphs significantly differed between M. galloprovincialis and M. edulis populations. The comparison of six mac-1 intron sequences over 277 bp showed at once that allelomorphs encompassed alleles differing from one another by substantial numbers of mutations, and that identical alleles were present in both M. galloprovincialis and M. edulis individuals, a probable result of the recent introgression between the two species.

Actins↗
PubMed1995

Sequence analysis and transcriptional mapping of the orf-2 gene of Autographa californica nuclear polyhedrosis virus.

Sequencing of the dnapol promoter region of Autographa californica nuclear polyhedrosis virus (AcNPV) revealed an overlapping open reading frame (ORF) in an antisense orientation, referred to as ORF-2. Analysis of the ORF-2 deduced amino-acid sequence revealed two short regions of homology with a similar ORF from Lymantria dispar nuclear polyhedrosis virus (LdNPV). Two 3' processing signals of this gene, expressed late during infection, were shown to be located on the orf-2 stop codon and 162 nucleotides further downstream.

Amino Acid Sequence↗
PubMed1994

Temporal regulation of a complex and unconventional promoter by viral products.

The DNA polymerase (dnapol) gene of Autographa californica nuclear polyhedrosis virus presents a complex promoter organization. It lacks the usual TATA box and start site, and its RNA accumulation initially increases and then decreases dramatically during infection. We investigated dnapol temporal regulation. Transiently expressed dnapol gene was transcribed at a low level from minor start sites. Coexpression with ie0 and/or ie1 immediate-early genes dramatically enhanced dnapol transcription, specifically from a new start site. Moreover, the ie1 transactivation required little or no information in front of this nonconventional proximal promoter. We showed that IE0 and IE1 proteins were stably expressed during infection and that the dnapol mRNA level decrease was not a consequence of the disappearance of these proteins. The dnapol promoter region contains a putative overlapping open reading frame (ORF) in the opposite direction. We showed that ORF-2 was indeed highly expressed late, when the dnapol mRNA level decreased, and that during that time, dnapol mRNA stability was not significantly altered, excluding a destabilizing antisense effect. Additionally, we showed that the dnapol promoter was inhibited late but not early during the infection of cells transiently expressing constructs carrying either the intact or the altered ORF-2 promoter. Therefore, ORF-2 initiation of transcription and dnapol promoter inhibition are two coincidental nonrelated phenomena. Finally, we showed that both IE1 transactivation and late inhibition occurred in the same limited region around the dnapol promoter.

Animals↗
PubMed1987

[Posturography should be included in the vertigo test].

After a brief review of different systems involved in postural control, we describe a method of posturography for exploring vestibulospinal pathways, in which postural oscillations of subject standing on a platform are recorded with eyes open then with eyes closed, and in different head and gaze positions. In normals, only closing of eyes interferes significantly with balance. Posturography is important in vertigo examinations, because it can show: vestibuloocular and vestibulospinal pathway lesions, associated or not; whether there is compensation for imbalance by visual input; cervical origin of vertigo, if any; and, in acute vestibular deficit, that good test results suggest a favorable prognosis.

Adult↗
PubMed1986

[Neurinomas with normal brain stem auditory evoked potentials].

Of 145 neurinomas operated upon, 2% had normal brain stem auditory evoked potentials (BERA). Potentials were obtained by means of a special technique allowing extraction every 600 ms and its follow up with time (brain stem temporal dynamic). This score of 2% was also that reported by some American authors who associate electrocochleography with BERA. The latter provide an accurate diagnosis in 96% of cases of all types of tumors taken together and in 91% of cases of small tumors. Furthermore, the performance of conventional scan imaging is accurate in only 25% of small tumors whereas gas meatocysternography detects more than 95% of cases. The latter method is therefore the most sensitive one but it possesses the disadvantage of being invasive and of costing much more than BERA, which remains therefore the least invasive examination providing the best and earliest diagnosis.

Brain Stem↗
PubMed1983

Maturational and degenerative processes in the organ of Corti after neonatal hypothyroidism.

In order to study the long-term effects of neonatal hypothyroidism on the organ of Corti, rats were given propylthiouracil (PTU) during the first 30 days after birth. Cochlear changes occurring after the cessation of antithyroid treatment were studied by both physiological (brainstem auditory evoked responses: BAERs, electrocochleography) and morphological techniques (transmission and scanning electron microscopy). The first appearance of BAERs was noted between days 37 and 45. Maturation of auditory potentials was achieved within 10-15 days but was incomplete since the animals definitely demonstrated elevated thresholds around 60-70 dB SPL. Morphological results indicated that some structures, like the inner sulcus epithelium, were able to restart maturational processes that had been interrupted during the period of hypothyroidism. However, these maturational changes were considerably limited and rapidLy accompanied by severe degenerative changes involving almost all cochlear structures. Degenerative changes included the deposition of an amorphous substance within the organ of Corti, severe alterations in pillar cells (absence of formation of the tunnel of Corti, distortion of microtubules), severe outer hair cell losses with abnormalities in their innervation (absence of development of efferents and loss of afferent dendrites).

Aging↗
PubMed1975

[Human Scarpa ganglion cell sheath].

The ganglion vestibulare (Scarpa) has been studied with the electron microscope on thirteen operative specimens (neurectomy for Meniere's vertigo) and two random autopsy specimens. Neuroganglionar cell bodies are enclosed in a Schwann sheath, without any myelin. This observation is at variance with previous descriptions in various vertebrate forms.

Humans↗
PubMedDate not supplied

Effects of hypothyroidism on the structural development of the organ of Corti in the rat.

The structural development of the organ of Corti was studied in 30 rat pups rendered hypothyroid by daily administration of propylthiouracil during the first 35 days after birth. Cochlear changes were observed by light microscopy and electronmicroscopy. Hypothyroid rat pups were found to have severe abnormalities in the organ of Corti. There was an abnormally prolonged persistence of Kölliker's organ and striking distortion of the tectorial membrane. The sensory epithelium exhibited marked signs of immaturity: the tunnel of Corti has not opened yet in animals 35 days old, sensory and supporting cells presented immature characteristics with abnormal persistence of the kinocilium. It is suggested that hypothyroidism results in an overall retardation of the maturation of cochlear structures and ultrastructural changes that appear to be significant enough to account for the hearing loss.

Animals↗
PubMedDate not supplied

Computer-assisted ABR interpretation using the automatic construction of the latency-intensity curve.

In this paper, we present a new computerised technique for the automatic construction of the latency intensity curve (LI curve). We take a pattern recognition approach determined by a priori information. We use knowledge gained from the audiogram and from physiological considerations. Therefore, we consider all recordings at different intensities as well as results from the extraction of a single auditory brainstem response (ABR) at a given stimulus intensity. We tested our method successfully: it allows us to prevent misrecognition errors in response detection or in latency measurements. Automatic recognition of the waves and recognition by the ear, nose and throat (ENT) specialist coincided in at least 90 per cent of cases. For wave V, the average deviation between the response thresholds given by our automatic recognition algorithm and those given by the ENT specialist was 5 dB, and the average deviation of the latencies was 0.05 ms.

Auditory Threshold↗