MicroRNAs in skeletal muscle and their regulation with exercise, ageing, and disease

Skeletal muscle makes up approximately 40% of the total body mass, providing structural support and enabling the body to maintain posture, to control motor movements and to store energy. It therefore plays a vital role in whole body metabolism. Skeletal muscle displays remarkable plasticity and is able to alter its size, structure and function in response to various stimuli; an essential quality for healthy living across the lifespan. Exercise is an important stimulator of extracellular and intracellular stress signals that promote positive adaptations in skeletal muscle. These adaptations are controlled by changes in gene transcription and protein translation, with many of these molecules identified as potential therapeutic targets to pharmacologically improve muscle quality in patient groups too ill to exercise. MicroRNAs (miRNAs) are recently identified regulators of numerous gene networks and pathways and mainly exert their effect by binding to their target messenger RNAs (mRNAs), resulting in mRNA degradation or preventing protein translation. The role of exercise as a regulatory stimulus of skeletal muscle miRNAs is now starting to be investigated. This review highlights our current understanding of the regulation of skeletal muscle miRNAs with exercise and disease as well as how they may control skeletal muscle health.

MicroRNAs in a hypertrophic heart: from foetal life to adulthood

The heart is the first organ to form and undergoes adaptive remodelling with age. Ventricular hypertrophy is one such adaptation, which allows the heart to cope with an increase in cardiac demand. This adaptation is necessary as part of natural growth from foetal life to adulthood. It may also occur in response to resistance in blood flow due to various insults on the heart and vessels that accumulate with age. The heart can only compensate to this increase in workload to a certain extent without losing its functional architecture, ultimately resulting in heart failure. Many genes have been implicated in cardiac hypertrophy, however none have been shown conclusively to be responsible for pathological cardiac hypertrophy. MicroRNAs offer an alternative mechanism for cellular regulation by altering gene expression. Since 1993 when the function of a non-coding DNA sequence was first discovered in the model organism Caenorhabditis elegans, many microRNAs have been implicated in having a central role in numerous physiological and pathological cellular processes. The level of control these antisense oligonucleotides offer can often be exploited to manipulate the expression of target genes. Moreover, altered levels of microRNAs can serve as diagnostic biomarkers, with the prospect of diagnosing a disease process as early as during foetal life. Therefore, it is vital to ascertain and investigate the function of microRNAs that are involved in heart development and subsequent ventricular remodelling. Here we present an overview of the complicated network of microRNAs and their target genes that have previously been implicated in cardiogenesis and hypertrophy. It is interesting to note that microRNAs in both of these growth processes can be of possible remedial value to counter a similar disease pathophysiology.

Does the ring species concept predict vocal variation in the crimson rosella, Platycercus elegans, complex?

Vocal variation may be important in population divergence. We studied geographical variation in contact calls of parrots of the crimson rosella, Platycercus elegans, complex, which is characterized by striking geographical plumage coloration variation. This complex has long been considered a rare example of a ring species (where two divergent forms coexist in sympatry but are connected by a chain of intermediate populations forming a geographical ring). We tested whether contact call variation is consistent with the ring species hypothesis. We recorded calls throughout the ring, including several sites from the three main population groups forming the ring and interfaces between them. We analysed duration, peak frequency, fundamental frequency and frequency modulation. We found significant differences, particularly in fundamental frequency and frequency modulation, at multiple biogeographical scales ranging from local populations to subspecies level. Discriminant function analyses showed some populations could be reliably discriminated from call structure. However, our results provided little support for three key predictions of the ring species hypothesis: (1) calls of the terminal, most divergent forms were not significantly different in three of the four acoustic variables, and differences did not appear to be maintained in sympatry, (2) phenotypically/geographically intermediate populations were not characterized by intermediate calls, and (3) call variation was not concordant with geographical sequence around the ring from one terminal form to the other. Our results underscore the emerging view that the evolutionary histories and phenotypic variability of many long-held ring species may be inadequately described by the ring species hypothesis and require alternative explanations. (C) 2008 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

Seeing the light : diet related variation in the vision of Platycercus elegans

 Poster Presentation

Fruitful use of bioacoustic alarm stimuli as a deterrent for Crimson Rosellas (Platycercus elegans)

Birds cause considerable damage to horticultural crops in Australia each year. The playback of species-specific bioacoustic alarm stimuli has been one of the most promising methods suggested to deal with bird-problems. However, no published studies have tested this method on species of parrots, one of the main avian pests of crops in Australia and globally. Furthermore the effectiveness of this method might be reduced if alarm calls were played back that came from a non-local population. The Crimson Rosella species complex (Platycercus elegans), a parrot with considerable acoustic variation throughout its range, is considered a pest species of several commercial fruit crops. This study tested whether alarm calls from Crimson Rosellas were effective in reducing the activity of Rosellas in apple orchards. Three groups of bioacoustic stimuli were compared: control stimuli, local alarm calls and non-local alarm calls. Our results indicate that the playback of alarm calls from Crimson Rosellas is effective in reducing the activity of Rosellas in orchards over the period of study, and we did not find any difference between the use of local and non-local alarm calls. Our study suggests that playback of alarm calls may be an effective deterrent of rosellas over a broad distribution, at least for short- to medium-term use.

Is there variation in the response to contact call playbacks across the hybrid zone of the parrot Platycercus elegans?

Learned vocal signals could be important in the formation of prezygotic isolation between two hybridising taxa. This study examined whether vocal variation in the parrot Platycercus elegans facilitates the separation of individuals from two subspecies, P. e. elegans (CR) and P. e. flaveolus (YR). CR and YR have very different plumage coloration, respectively deep crimson and pale yellow, but hybridise where they meet creating an intermediate population (WS). In a factorial design playback experiment, we conducted 108 playback trials on three focal populations (YR, WS, CR), in and around this area of hybridisation, to test if they respond differently to contact calls from their own or another population. We also analysed whether differences in acoustic variables of the stimulus calls predicted the response to the call. We did not find any indication that individuals from the three focal populations responded differently to calls sampled from their own or another subspecies. We did find an effect of two of the five acoustic variables that we used to describe and classify contact calls from the three source populations. Specifically, duration of the stimulus call positively affected the response from individuals from WS and negatively the response from CR, and CR responded more to stimulus calls with a lower peak frequency. Overall, we found no indication that acoustic variation in contact calls on a subspecies level is involved in maintaining plumage colour differences between P. e. elegans and P. e. flaveolus subspecies.

Prevalence of beak and feather disease virus in wild Platycercus elegans: comparison of three tissue types using a probe-based real-time qPCR test

The detection of avian viruses in wild populations has considerable conservation implications. For DNA-based studies, feathers may be a convenient sample type for virus screening and are, therefore, an increasingly common technique. This is despite recent concerns about DNA quality, ethics, and a paucity of data comparing the reliability and sensitivity of feather sampling to other common sample types such as blood. Alternatively, skeletal muscle tissue may offer a convenient sample to collect from dead birds, which may reveal viraemia. Here, we describe a probe-based quantitative real-time PCR for the relative quantification of beak and feather disease virus (BFDV), a pathogen of serious conservation concern for parrots globally. We used this method to test for BFDV in wild crimson rosellas (Platycercus elegans), and compared three different sample types. We detected BFDV in samples from 29 out of 84 individuals (34.5%). However, feather samples provided discordant results concerning virus presence when compared with muscle tissue and blood, and estimates of viral load varied somewhat between different sample types. This study provides evidence for widespread infection of BFDV in wild crimson rosellas, but highlights the importance of sample type when generating and interpreting qualitative and quantitative avian virus data.

The ecology and evolution of beak and feather disease virus in Platycercus elegans

 This thesis explores the complex ecological and evolutionary interactions between beak and feather disease virus and one of its hosts the crimson rosella. The work identifies several factors that predict viral infection in wild birds and determines how host population structure influences viral evolution.

A Wuchiapingian (Late Permian) brachiopod fauna from an exotic block in the Indus–Tsangpo suture zone, southern Tibet, and its palaeobiogeographical and tectonic implications

A brachiopod fauna including 19 species of 17 genera from an exotic block in the Indus–Tsangpo suture zone in southern Tibet is described and illustrated. The brachiopod fauna is dominated by Martinia elegans and two new taxa: Jinomarginifera lhazeensis gen. et sp. nov. and Zhejiangospirifer giganteus sp. nov. The fauna is closely comparable with those from the middle and upper parts of the Wargal Formation and the Chhidru Formation in the Salt Range of Pakistan, the Chitichun Limestone in southern Tibet, and the Basleo area of West Timor, and these correlations suggest a Wuchiapingian age. The fauna exhibits substantial links with both peri–Gondwanan and Cathaysian faunas, which may imply that it is a seamount biota originally located in the southern margin of the Neotethys during the Late Permian, and was later (in the early Cenozoic) displaced and became sandwiched into younger marine deposits in the collision process between India and Eurasia.

Avian retinal oil droplets : dietary manipulation of colour vision?

Avian vision is highly developed, with bird retinas containing rod and double-cone photoreceptors, plus four classes of single cones subserving tetrachromatic colour vision. Cones contain an oil droplet, rich in carotenoid pigments (except VS/ultraviolet-sensitive cones), that acts as a filter, substantially modifying light detected by the photoreceptor. Using dietary manipulations, we tested the effects of carotenoid availability on oil droplet absorbance properties in two species: Platycercus elegans and Taeniopygia guttata. Using microspectrophotometry, we determined whether manipulations affected oil droplet carotenoid concentration and whether changes would alter colour discrimination ability. In both species, increases in carotenoid concentration were found in carotenoid-supplemented birds, but only in the double cones. Magnitudes of effects of manipulations were often dependent on retinal location. The study provides, to our knowledge, the first experimental evidence of dietary intake over a short time period affecting carotenoid concentration of retinal oil droplets. Moreover, the allocation of carotenoids to the retina by both species is such that the change potentially preserves the spectral tuning of colour vision. Our study generates new insights into retinal regulation of carotenoid concentration of oil droplets, an area about which very little is known, with implications for our understanding of trade-offs in carotenoid allocation in birds.

Where and when does a ring start and end? Testing the ring-species hypothesis in a species complex of Australian parrots

Speciation, despite ongoing gene flow can be studied directly in nature in ring species that comprise two reproductively isolated populations connected by a chain or ring of intergrading populations. We applied three tiers of spatio-temporal analysis (phylogeny/historical biogeography, phylogeography and landscape/population genetics) to the data from mitochondrial and nuclear genomes of eastern Australian parrots of the Crimson Rosella Platycercus elegans complex to understand the history and present genetic structure of the ring they have long been considered to form. A ring speciation hypothesis does not explain the patterns we have observed in our data (e.g. multiple genetic discontinuities, discordance in genotypic and phenotypic assignments where terminal differentiates meet). However, we cannot reject that a continuous circular distribution has been involved in the group's history or indeed that one was formed through secondary contact at the 'ring's' east and west; however, we reject a simple ring-species hypothesis as traditionally applied, with secondary contact only at its east. We discuss alternative models involving historical allopatry of populations. We suggest that population expansion shown by population genetics parameters in one of these isolates was accompanied by geographical range expansion, secondary contact and hybridization on the eastern and western sides of the ring. Pleistocene landscape and sea-level and habitat changes then established the birds' current distributions and range disjunctions. Populations now show idiosyncratic patterns of selection and drift. We suggest that selection and drift now drive evolution in different populations within what has been considered the ring.