Induction of cell fate in the Drosophila retina: the bride of sevenless protein is predicted to contain a large extracellular domain and seven transmembrane segments

Previous genetic mosaic studies established that expression of the Drosophila bride of sevenless (boss) gene is required in photoreceptor neuron R8 for the development of photoreceptor neuron R7. This led to the proposal that boss encodes or regulates an R7-specific inductive cue. We have identified the boss gene based on small deletions in mutant alleles and sequenced both cDNAs and corresponding genomic regions. One P element and three X-ray-induced boss alleles show different deletions in the gene ranging in size from 2 to 23 bp, each causing frameshifts leading to premature termination of translation. The boss gene encodes a protein of 896 amino acids with a putative amino-terminal signal sequence, a large extracellular region of 498 amino acids, and seven potential transmembrane domains followed by a carboxy-terminal cytoplasmic tail of 115 amino acids. The putative membrane localization of the boss protein is consistent with a model in which direct interaction between the boss and sevenless proteins specifies R7 cell fate. Another model in which the boss protein functions as a receptor is proposed based on its similarity to the G protein-linked family of membrane receptors.     

Listeria monocytogenes peritonitis associated with CAPD

Listeria monocytogenes peritonitis developed in a 67-year-old man on continuous ambulatory peritoneal dialysis following a catered luncheon. Alcoholic liver disease was a predisposing factor. L. monocytogenes multiplies at 4 degrees C. It is often present in imported soft cheese, less often in chicken and other refrigerated food. Listeria peritonitis has not been previously reported in Australia.     

Hypoxia facilitates tumour cell detachment by reducing expression of surface adhesion molecules and adhesion to extracellular matrices without loss of cell viability.

The effects of acute hypoxia on integrin expression and adhesion to extracellular matrix proteins were investigated in two human melanoma cell lines, HMB-2 and DX3, and a human adenocarcinoma cell line, HT29. Exposure to hypoxia caused a significant down-regulation of cell surface integrins and an associated decrease in cell adhesion. Loss of cell adhesion and integrin expression were transient and levels returned to normal within 24 h of reoxygenation. Other cell adhesion molecules, such as CD44 and N-CAM, were also down-regulated after exposure of cells to hypoxia. Acute exposure to hypoxia of cells at confluence caused rapid cell detachment. Cell detachment preceded loss of viability. Detached HMB-2 and DX3 cells completely recovered upon reoxygenation, and floating cells re-attached and continued to grow irrespective of whether they were left in the original glass dishes or transferred to new culture vessels, while detached HT29 cells partly recovered upon reoxygenation. Cell detachment after decreased adhesion appears to be a stress response, which may be a factor enabling malignant cells to escape hypoxia in vivo, with the potential to form new foci of tumour growth.     

The effect of a single large dose of amoxycillin on oral streptococci

Salivary samples were examined for a period three weeks before, and three weeks after the administration of 3 g of amoxycillin in ten volunteers. There was a marked drop in the concentration of streptococci in all subjects in the first 4 h but most had substantially recovered within 48 h. All had recovered at seven days. No strains were resistant to 1 mg/l amoxycillin in the pre-treatment control series, and no resistant streptococci emerged.     

Hydranencephaly in an infant with vascular malformations

Hydranencephaly is a condition in which cerebral hemispheres are absent and reduced to fluid‐filled sacs in a normal skull. Numerous causes have been proposed. We report a male infant with hydranencephaly and congenital vascular malformations (port wine stains, generalized nevus flammeus, anomalous retinal vessels, and absent internal carotid flow). Magnetic resonance imaging of the brain showed absence of most of the cerebrum except for small portions of the occipital cortex and thalami. Magnetic resonance angiography showed flow within the vertebral and basilar arteries without internal carotid intracranial flow above the internal carotid petrous and cavernous portion. This is a report of cutaneous and retinal malformations associated with hydranencephaly. Vascular malformations of larger vessels (e.g., webbing of the carotid arteries and an absent internal carotid arterial system) have been observed in other infants with hydranencephaly, and are proposed to lead to brain destruction. The case reported herein supports the role of primary vascular malformations in the development of some cases of hydranencephaly. © 2001 Wiley‐Liss, Inc.     

Biomechanical comparison of a novel multilevel hex-head pedicle screw design with a conventional head design.

The objective of the study was to determine the biomechanical effect during insertion of multilevel hex-head design pedicle screws compared to a conventional screw-head design. Eighteen lumbar vertebrae and thoracic vertebrae from human cadavers were instrumented with a novel, multilevel hexagonal head pedicle screw on one side and a conventional head pedicle screw on the contralateral side. Screws were inserted at a constant rate and insertion and removal torques were recorded. A further 14 lumbar and thoracic vertebrae were used to test alterability of screw direction and operational effort required. Electromagnetic sensors recorded the change in angular direction for both screw and screwdriver. The force applied through the insertion screwdriver required to produce the directional change was also recorded. No significant differences were found between the two screw types for insertion or removal torque in either lumbar or thoracic vertebrae. Multilevel hex-head screws had significantly greater directional alterability than conventional head screws in both lumbar and thoracic specimens. Multilevel hex-head screws also required less force applied through the screwdriver than conventional screws to alter direction of screw insertion in both lumbar and thoracic specimens. The multilevel hex-head design did not affect the insertion or removal torque in comparison to a conventional head design.     

Mid-trimester loss--appraisal of a screening protocol

The main causes for mid-trimester loss are known. There is likely to be overlap with those of first trimester loss, but the proportions may be different. We wished to perform an aetiological survey in a large population of patients with a history of recurrent miscarriage, for possible explanations for their second trimester miscarriages. Database analysis of 636 patients attending a UK University Teaching Hospital dedicated miscarriage clinic between 1991 and 1996 revealed a 25% prevalence (n = 158) for second trimester miscarriage. Results from an investigative screening protocol were positive in 50% of cases: 33% (n = 52) tested positive for antiphospholipid syndrome (APS); 8% (n = 13) fulfilled strict criteria for cervical incompetence; there was a 4% prevalence of uterine anomaly; 3% for infection (n = 5) and 2% of patients (n = 3) proved to be hypothyroid. Importantly, dual pathology was found in 5% of patients with a history of second trimester miscarriage. As idiopathic mid-trimester loss is a diagnosis by exclusion, a high index of suspicion is required, as are modern diagnostic techniques.      

A circadian study of liver antioxidant enzyme systems of female Fischer-344 rats subjected to dietary restriction for six weeks.

We examined the influences of dietary restriction (DR) on the circadian profile of liver catalase (CAT), glutathione peroxidase (GPx), and interacting systems required for removal of H₂O₂ (support systems), in 18-week old female Fischer 344 rats fed 60% of their ad libitum (AL) diet for six weeks. Food was presented to the DR animals during the early light-span. Regardless of diet, enzyme levels were generally consistent with circadian patterns. In CR animals, maximum activities often occurred at the time of food presentation. CAT and GPx activities generally were significantly higher in DR animals than in AL animals at the time of feeding. When assessing glucose-6-phosphate dehydrogenase (G6PDH) activity using saturating substrate (NADP⁺) concentrations, higher activities were seen at all times of day in the AL animals; however, when activity was measured in the presence of lower (i.e., physiologic) NADP⁺ concentrations, the reverse was true. In contrast, glutathione reductase (GR) activity was not influenced by DR. Cytosolic levels of NADPH peaked and were higher in DR than in AL rodents prior to feeding. NADH levels were not influenced by diet, but did manifest a significant circadian pattern with a maximum occurring toward the middle of the dark span. These data suggest that even at a young age and following only a relatively brief duration of DR, there exists an enhanced enzymatic capability in rats subjected to DR to remove free radicals generated as a consequence of normal oxidative metabolism. Further, these data support emerging trends suggesting metabolic regulation of antioxidant defense systems in response to free radical generation.     

Improved recovery of antibiotic-stressed microorganisms on inclusion of saponin in aerobic blood culture media

The recovery rates and times to detection of microorganisms isolated from two similar blood culture media, one containing saponin, were compared. A total of 2117 blood cultures were analysed in a prototype automated blood culture system. Significantly more gram-positive organisms (P<0.05) and gram-negative organisms (P<0.05), includingEnterobacterlaceae (P<0.05) were recovered from the lytic medium. Average time to detection in the lytic medium was 15.8 h, compared to 22.7 h in the other medium (P<0.001). The improved recovery of microorganisms was most pronounced in blood samples obtained from patients being treated with antibiotics at the time of venesection. In vitro experiments on antibiotic affected bacteria confirmed the protective effect of saponin.