Glial cells mediate target layer selection of retinal axons in the developing visual system of Drosophila

In the fly visual system, each class of photoreceptor neurons (R cells) projects to a different synaptic layer in the brain. R1-R6 axons terminate in the lamina, while R7 and R8 axons pass through the lamina and stop in the medulla. As R cell axons enter the lamina, they encounter both glial cells and neurons. The cellular requirement for R1-R6 targeting was determined using loss-of-function mutations affecting different cell types in the lamina. nonstop (encoding a ubiquitin-specific protease) is required for glial cell development and hedgehog for neuronal development. Removal of glial cells but not neurons disrupts R1-R6 targeting. We propose that glial cells provide the initial stop signal promoting growth cone termination in the lamina. These findings uncover a novel function for neuron-glial interactions in regulating target specificity.

brakeless is required for photoreceptor growth-cone targeting in Drosophila

The R1-R6 subclass of photoreceptor neurons (R cells) in the Drosophila compound eye form specific connections with targets in the optic ganglia. In this paper, we report the identification of a gene, brakeless (bks), that is essential for R1-R6 growth cone targeting. In brakeless mutants, R1-R6 growth cones frequently fail to terminate migration in their normal target, the lamina, and instead project through it and terminate in the second optic ganglion, the medulla. Genetic mosaic analysis and transgene rescue experiments indicate that bks functions in R cells and not within the lamina target region. bks encodes a nuclear protein. We propose that it participates in a gene expression pathway regulating one or more growth cone components controlling R1-R6 targeting.

Practice compared. The UK and Australia

OBJECTIVE

To compare the processes and cost of management of chronic health problems between a rural general practice in the UK and a similar practice in Australia. Patients were selected from three groups with either diabetes, asthma or depression.

DESIGN

Case study, retrospective. This comparison was conducted during a 6 month practice exchange.

SETTING

Wagin, Western Australia and Berwick upon Tweed, England.

SUBJECTS

Ten people (five men, five women) were selected from each practice, for each disease type. Their records were culled and compared on the basis of how well they had satisfied the requirements of the protocols (where they existed) on the management of each disease. Other comparisons also included the number and cost of consultations, prescriptions and hospital stays.

RESULTS

There was no apparent difference in the age/sex distributions of the populations studied. Comparisons of the three disease groups showed: Asthma-results similar on most counts, except hospital admissions. Protocol uniformly poorly followed. Diabetes-results similar, except use/cost of prescription drugs which was much greater in Australia. The UK was much better following its protocol. Depression-Australia again used significantly more prescription drugs. The use and cost of GP/specialist visits was higher overall in Australia.

CONCLUSION

This study suggests that a rural UK practice provides more cost effective review of chronic health problems. Further study would be warranted to investigate the impression that this was achieved at the expense of patient and doctor satisfaction.

The storage form of vitamin A in rat liver cells

After collagenase treatment of perfused rat liver, isolated washed hepatocytes (parenchymal cells) and washed nonparenchymal cells contained 13-53% and 5-9%, respectively, of the total vitamin A in rat liver. After Pronase E and DNase digestion of liver, nonparenchymal cells contained 1-6% of the total liver vitamin A content. By density-gradient centrifugation, hepatocytes were divided into six fractions, which contained fewer lipid globules per cell and less vitamin A per cell as the cell density increased. In our procedures, lipocytes could not be isolated after either collagenase or pronase E and DNase digestion of liver. Of the total liver vitamin A, 40-80% was found in very low density, vitamin A-containing globules, which have a median diameter of 1.7 microns (range 0.4-4.6 microns), show intense yellow-green fluorescence under UV illumination and contain greater than 95% of their vitamin A in ester form. The distribution of vitamin A among cells and vitamin A globules in rats dosed with vitamin A was the same as in undosed rats. The possible interaction of lipocytes and different classes of hepatocytes in the storage and mobilization of vitamin A is discussed.