Genetics and physiological expression of β-hydroxy acid dehydrogenase in Drosophila

A mutant Had ^nl was induced in Drosophila melanogaster and found to be deficient in -hydroxy acid dehydrogenase. This mutation was utilized to study the genetics and physiological expression of Had ⁺. Had⁺ was mapped to the X chromosome at 54.4 and seems to be the structural gene for the enzyme. Enzyme activity in male and female flies indicates that the gene shows both dosage compensation independent from dose effect and differential activity during ontogeny. Electrophoretic mobility data indicate that the enzyme is a dimer which forms by random association of subunits. The fact that the mutant shows no detrimental effect implies that the enzyme is dispensable, at least under laboratory conditions. The biological and technical implications of this gene-enzyme system are discussed.This research was sponsored by the Energy Research and Development Administration under contract with the Union Carbide Corporation. J. E. T. was a postdoctoral investigator supported by USPHS Fellowship No. 1-F02-GM53673-01 during a portion of this work.     

Long photoperiod restores the 24-h rhythm of sleep and EEG slow-wave activity in the Djungarian hamster (Phodopus sungorus)

Photoperiod influences the distribution of sleep and waking and electroencephalogram (EEG) power density in the Djungarian hamster. In an experimental procedure combining short photoperiod (SP) and low ambient temperature, the light-dark difference in the amount of sleep was decreased, and the changes in slow-wave activity (SWA) (mean EEG power density between 0.75 and 4.0 Hz) in nonrapid eye movement (NREM) sleep within 24 h were abolished. These findings, obtained in three different groups of animals, suggested that at the lower ambient temperature, the influence of the circadian clock on sleep-wake behavior was diminished. However, it remained unclear whether the changes were due to the photoperiod, ambient temperature, or both. Here, the authors show that EEG and electromyogram recordings in a single group of animals sequentially adapted to a short and long photoperiod (LP) at low ambient temperature (approximately 15 degrees C) confirm that EEG power is reduced in SP. Moreover, the nocturnal sleep-wake behavior and the changes in SWA in NREM sleep over 24 h were restored by returning the animals to LP and retaining ambient temperature at 15 degrees C. Therefore, the effects cannot be attributed to ambient temperature alone but are due to a combined effect of temperature and photoperiod. When the Djungarian hamster adapts to winter conditions, it appears to uncouple sleep regulation from the circadian clock.     

Surface Microstructures on Planar Substrates and Textile Fibers Guide Neurite Outgrowth: A Scaffold Solution to Push Limits of Critical Nerve Defect Regeneration?

The treatment of critical size peripheral nerve defects represents one of the most serious problems in neurosurgery. If the gap size exceeds a certain limit, healing can''t be achieved. Connection mismatching may further reduce the clinical success. The present study investigates how far specific surface structures support neurite outgrowth and by that may represent one possibility to push distance limits that can be bridged. For this purpose, growth cone displacement of fluorescent embryonic chicken spinal cord neurons was monitored using time-lapse video. In a first series of experiments, parallel patterns of polyimide ridges of different geometry were created on planar silicon oxide surfaces. These channel-like structures were evaluated with and without amorphous hydrogenated carbon (a-C:H) coating. In a next step, structured and unstructured textile fibers were investigated. All planar surface materials (polyimide, silicon oxide and a-C:H) proved to be biocompatible, i.e. had no adverse effect on nerve cultures and supported neurite outgrowth. Mean growth cone migration velocity measured on 5 minute base was marginally affected by surface structuring. However, surface structure variability, i.e. ridge height, width and inter-ridge spacing, significantly enhanced the resulting net velocity by guiding the growth cone movement. Ridge height and inter-ridge distance affected the frequency of neurites crossing over ridges. Of the evaluated dimensions ridge height, width, and inter-ridge distance of respectively 3, 10, and 10 µm maximally supported net axon growth. Comparable artificial grooves, fabricated onto the surface of PET fibers by using an excimer laser, showed similar positive effects. Our data may help to further optimize surface characteristics of artificial nerve conduits and bioelectronic interfaces.     

Fine structural analysis of the thoracic longitudinal stripes of Zaprionus vittiger (Diptera)

The structure of the longitudinal zebra stripes on the thorax of adult Zaprionus vittiger has been investigated by light-, polarization-, transmission electron-, and scanning electron microscopy. Each stripe consists of a central white stripe of about 50 μm width and two lateral dark brown stripes about 30 μm wide. Three different types of trichomes occur: Very long bent trichomes of the grooved-type, long bent trichomes of the crested-type, and short straight trichomes. The central white stripe contains neither bristle organs nor short straight trichomes but carries many long bent trichomes most of which are of the grooved type, contain two cavities and polarize the light in the polarization microscope. The dark brown stripes carry bristle organs and many trichomes of the short and straight-type. Bent trichomes of the crested-type are found on the whole zebra stripe at about equal frequencies; they contain no cavities and do not polarize the light. The cuticle of the dark stripes is underlain by pigment cells. It is suggested that the pigment granules in the epidermal cells cause the dark color of the dark brown stripes, whereas the form and structure of the bent grooved type trichomes cause the white color of the central stripe.     

Oxidative stress and life histories: unresolved issues and current needs

Life‐history theory concerns the trade‐offs that mold the patterns of investment by animals between reproduction, growth, and survival. It is widely recognized that physiology plays a role in the mediation of life‐history trade‐offs, but the details remain obscure. As life‐history theory concerns aspects of investment in the soma that influence survival, understanding the physiological basis of life histories is related, but not identical, to understanding the process of aging. One idea from the field of aging that has gained considerable traction in the area of life histories is that life‐history trade‐offs may be mediated by free radical production and oxidative stress. We outline here developments in this field and summarize a number of important unresolved issues that may guide future research efforts. The issues are as follows. First, different tissues and macromolecular targets of oxidative stress respond differently during reproduction. The functional significance of these changes, however, remains uncertain. Consequently there is a need for studies that link oxidative stress measurements to functional outcomes, such as survival. Second, measurements of oxidative stress are often highly invasive or terminal. Terminal studies of oxidative stress in wild animals, where detailed life‐history information is available, cannot generally be performed without compromising the aims of the studies that generated the life‐history data. There is a need therefore for novel non‐invasive measurements of multi‐tissue oxidative stress. Third, laboratory studies provide unrivaled opportunities for experimental manipulation but may fail to expose the physiology underpinning life‐history effects, because of the benign laboratory environment. Fourth, the idea that oxidative stress might underlie life‐history trade‐offs does not make specific enough predictions that are amenable to testing. Moreover, there is a paucity of good alternative theoretical models on which contrasting predictions might be based. Fifth, there is an enormous diversity of life‐history variation to test the idea that oxidative stress may be a key mediator. So far we have only scratched the surface. Broadening the scope may reveal new strategies linked to the processes of oxidative damage and repair. Finally, understanding the trade‐offs in life histories and understanding the process of aging are related but not identical questions. Scientists inhabiting these two spheres of activity seldom collide, yet they have much to learn from each other.     

Functional consequences of phenotypic variation between locally adapted populations: Swimming performance and ventilation in extremophile fish

Natural selection drives the evolution of traits to optimize organismal performance, but optimization of one aspect of performance can influence other aspects of performance. Here, we asked how phenotypic variation between locally adapted fish populations affects locomotion and ventilation, testing for functional trade‐offs and trait–performance correlations. Specifically, we investigated two populations of livebearing fish (Poecilia mexicana) that inhabit distinct habitat types (hydrogen‐sulphide‐rich springs and adjacent nonsulphidic streams). For each individual, we quantified different metrics of burst swimming during simulated predator attacks, steady swimming and gill ventilation. Coinciding with predictions, we documented significant population differences in all aspects of performance, with fish from sulphidic habitats exhibiting higher steady swimming performance and higher ventilation capacity, but slower burst swimming. There was a significant functional trade‐off between steady and burst swimming, but not between different aspects of locomotion and ventilation. Although our findings about population differences in locomotion performance largely parallel the results from previous studies, we provide novel insights about how morphological variation might impact ventilation and ultimately oxygen acquisition. Overall, our analyses provided insights into the functional consequences of previously documented phenotypic variation, which will help to disentangle the effects of different sources of selection that may coincide along complex environmental gradients.