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Biomedical subjects

B Appel

Publications and source records attributed to B Appel.

At least 37 records · Page 2Linked to original sources
PubMed1996

valentino: a zebrafish gene required for normal hindbrain segmentation.

Mutational analysis can serve both to identify new genes essential for patterning embryonic development and to determine their functions. Here we describe the identification and phenotypic characterization of alleles of valentino, which we recovered in a genetic screen that sought to identify mutations in the zebrafish that disrupt region-specific gene expression patterns in the embryonic brain. valentino is required for normal hindbrain segmentation and the hindbrain of valentino mutant embryos is shortened by the length of one rhombomere. We demonstrate that valentino is required cell-autonomously in the development of rhombomeres 5 and 6, and propose that valentino functions in the subdivision and expansion of a common precursor region in the presumptive hindbrain into the definitive rhombomeres 5 and 6. These results provide genetic evidence for a two-segment periodicity in the hindbrain and suggest that this periodicity arises sequentially, through the specification and later subdivision of a two-rhombomere unit, or 'protosegment'.

Animals↗
PubMed1995

Motoneuron fate specification revealed by patterned LIM homeobox gene expression in embryonic zebrafish.

In zebrafish, individual primary motoneurons can be uniquely identified by their characteristic cell body positions and axonal projection patterns. The fate of individual primary motoneurons remains plastic until just prior to axogenesis when they become committed to particular identities. We find that distinct primary motoneurons express particular combinations of LIM homeobox genes. Expression precedes axogenesis as well as commitment, suggesting that LIM homeobox genes may contribute to the specification of motoneuronal fates. By transplanting them to new spinal cord positions, we demonstrate that primary motoneurons can initiate a new program of LIM homeobox gene expression, as well as the morphological features appropriate for the new position. We conclude that the patterned distribution of different primary motoneuronal types within the zebrafish spinal cord follows the patterned expression of LIM homeobox genes, and that this reflects a highly resolved system of positional information controlling gene transcription.

Amino Acid Sequence↗
PubMed1993

Cell-type-specific mechanisms of transcriptional repression by the homeotic gene products UBX and ABD-A in Drosophila embryos.

The homeotic genes of Drosophila melanogaster, which are required for specification of segmental identities, encode proteins capable of regulating gene expression. We have chosen to study the organization and function of a regulatory target in an attempt to learn how homeotic gene products provide appropriate transcriptional controls. We identified 30 common binding sites for the proteins encoded by the Ultrabithorax (Ubx) and abdominal-A (abd-A) genes within a negatively regulated target, the P2 promoter of the Antennapedia (Antp) gene. By systematically mutagenizing binding sites and observing the resulting P2 expression pattern in embryos, we have found evidence for cell-type-specific interactions that are mediated by these sequences. In certain neuronal cells, UBX and ABD-A proteins appear to repress by competing for common binding sites with another homeodomain protein, which we propose to be ANTP acting to induce P2 transcription in an autoregulatory manner. In sets of cells that contribute to the tracheal system, UBX and ABD-A repress by counteracting the function of a factor acting at independent sites. The latter mechanism of repression requires only that multiple homeodomain binding sequences be present and is not dependent on any particular binding site.

Animals↗
PubMed1993

Database for serial magnetic resonance imaging in multiple sclerosis.

The unique sensitivity of magnetic resonance imaging (MRI) in detecting disease activity in multiple sclerosis (MS) and the objective nature of the information obtained suggest that MRI will be a useful and reliable way of monitoring treatment trials. There is a need to develop an appropriate database which would provide a standardised means of assessment, not only of MRI, but also of essential clinical information. As part of the program of Concerted Action in Multiple Sclerosis, funded by the Commission of the European Community (CEC), we have developed a database for recording serial brain MRI results. The database consists of core, entry and follow-up sections. Both entry and follow-up parts are subdivided into clinical, MR system and MRI data. We expect that the use of this database will maximise efficiency of MRI monitoring in MS treatment trials, particularly in multicentre studies.

Brain↗
PubMed1993

Extensive cervical intradural and intramedullary lipoma and spina bifida occulta of C1: a case report.

A 17-year-old boy presented with a 1-year history of progressive gait difficulties and slowing of fine hand movements. On neurological examination there was tetraspasticity, bilateral pes equinovarus and a decreased position sense in the feet. CT and MRI scan of the cervical spine demonstrated a spina bifida occulta of C1, an extensive intradural lipoma from the foramen magnum to C4 with a small intramedullary portion at C3, and a distal syringomyelia reaching down to D12. After excision of the extramedullary portion of the lipoma, there was a marked improvement of the gait and a reduction of the spasticity.

Adolescent↗
PubMed1992

Effects of insulin and dexamethasone on lipoprotein lipase in human adipose tissue.

The mechanisms by which insulin and glucocorticoids modulate lipoprotein lipase (LPL) synthesis and degradation were examined in human adipose tissue fragments maintained in organ culture. Tissue fragments were cultured for 7 days in serum-free medium supplemented with or without insulin (7 nM) and with or without dexamethasone (30 nM), a synthetic glucocorticoid. Responses of LPL activity to both insulin and dexamethasone were obtained at doses within the physiological range. At a maximal dose, insulin increased heparin-releasable and total LPL activity (approximately 7-fold) by specifically increasing the rate of LPL synthesis (approximately 5-fold) determined by pulse labeling with [35S]methionine and [35S]cysteine and immunoprecipitation. Dexamethasone added in the presence of insulin increased heparin-releasable and total LPL activity approximately 8-fold but did not alter rates of LPL synthesis compared with insulin alone. Pulse-chase studies showed that the rate of LPL degradation was markedly slowed in the presence of dexamethasone plus insulin compared with insulin alone. These data suggest that, in human adipose tissue, insulin is essential for maintaining rates of LPL synthesis and that cortisol may play a key role in regulating human adipose tissue LPL at the posttranslational level by inhibiting the degradation of newly synthesized LPL.

Adipose Tissue↗
PubMed1991

Slow progressive bilateral posterior artery infarction presenting as agitated delirium, complicated with Anton's syndrome.

Three patients presented with an acute agitated delirium as the earliest sign of bilateral posterior cerebral artery infarction. All patients showed a unique slow progressive deterioration with a remarkably long interval between the first neuropsychological and subsequent visual and neurological symptoms, ranging from 3 to 30 days. Repeated CT scans demonstrated hypodensities in the posterior artery territory only after a long interval of 9-12 days, in case 3, and between 33 and 48 days in case 2. In the latter case MRI was still negative 33 days after onset. In 2 patients the cortical blindness was complicated with anosognosia for blindness. Clinical condition worsened progressively in all patients, leading to death, probably due to brainstem infarction. In all 3, the combination of clinical and radiological findings indicated a 'top of the basilar' distribution, which could be confirmed in two by autopsy.

Aged↗
PubMed1991

Localized craniofacial fibrous dysplasia in a young girl.

We consider here the case of a young girl presenting a cystic bone mass in the left orbital roof. Although standard X-rays at first were not convincing, the findings on the CT examination and the histological aspect of the mass were typical of fibrous dysplasia. Although the exact diagnosis of fibrous dysplasia can only be made upon precise histological examination, radiological, and more specifically CT findings, may indicate this pathology.

Child↗
PubMed1991

Post-operative maxillary cyst associated with a maxillary sinus elevation procedure: a case report.

Proper diagnosis, treatment planning, and surgical manipulation of the posterior maxilla require a thorough knowledge of the anatomy, physiology, and pathology associated with the maxillary sinus. This case report of a post-operative maxillary cyst diagnosed following routine post-operative examination of a sinus elevation procedure illustrates the need for a meticulous surgical technique, proper management of complications, and routine, long-term follow-up. With the increased utilization of sinus elevation techniques, reports of this destructive lesion may become more common.

Aged↗
PubMed1990

Arachnoiditis ossificans with arachnoid cyst after cranial tuberculous meningitis.

A 34-year-old woman developed symptomatic arachnoiditis ossificans and an arachnoid cyst as a consequence of tuberculous meningitis adequately treated 20 years before. Surgical decompression of the cyst stopped the progression of her spastic paraparesis. Pathologic examination confirmed the presence of ossification of the arachnoid.

Adult↗