Peter D. Currie

The structure and evolution of the melanocortin and MCH receptors in fish and mammals

Zebrafish are an excellent genetic model system for studying developmental and physiological processes. Pigment patterns in zebrafish are affected by mutations in three types of chromatophores. The behavior of these cells is influenced by alpha-melanocyte-stimulating hormone (alphaMSH) and melanin-concentrating hormone (MCH). Mammals have five alphaMSH receptors (melanocortin receptors) and one or two MCH receptors. We have identified the full complement of melanocortin and MCH receptors in both zebrafish and the pufferfish, Fugu. Zebrafish have six melanocortin receptors, including two MC5R orthologues, while Fugu, lacking MC3R, has only four. We also demonstrate that Fugu and zebrafish have two and three MCHR genes, respectively. MC2R and MC5R are physically linked in all species examined. Unlike other species, we find the Fugu genes contain introns, one of which is in a conserved location and is probably ancestral. We also detail the differential expression of the zebrafish genes throughout development.

THE GENERATION AND INTERPRETATION OF POSITIONAL INFORMATION WITHIN THE VERTEBRATE MYOTOME

How somitic cells become restricted to the muscle fate has been investigated on a number of levels. Classical embryological manipulations have attempted to define the source of inductive signals that control the formation of the myotome. Recently, these studies have converged with others dissecting the role of secreted proteins in embryonic patterning to demonstrate a role for specific peptides in inducing individual cell types of the myotome. Collectively, these investigations have implicated the products of the Wnt, Hedgehog (Hh) and Bone morphogenetic protein (Bmp) gene families as key myogenic regulators; simultaneously controlling both the initiation of myogenesis and the fate of individual myoblasts.

FishNet: an online database of zebrafish anatomy

BackgroundOver the last two decades, zebrafish have been established as a genetically versatile model system for investigating many different aspects of vertebrate developmental biology. With the credentials of zebrafish as a developmental model now well recognized, the emerging new opportunity is the wider application of zebrafish biology to aspects of human disease modelling. This rapidly increasing use of zebrafish as a model for human disease has necessarily generated interest in the anatomy of later developmental phases such as the larval, juvenile, and adult stages, during which many of the key aspects of organ morphogenesis and maturation take place. Anatomical resources and references that encompass these stages are non-existent in zebrafish and there is therefore an urgent need to understand how different organ systems and anatomical structures develop throughout the life of the fish.ResultsTo overcome this deficit we have utilized the technique of optical projection tomography to produce three-dimensional (3D) models of larval fish. In order to view and display these models we have created FishNet http://www.fishnet.org.au, an interactive reference of zebrafish anatomy spanning the range of zebrafish development from 24 h until adulthood.ConclusionFishNet contains more than 36 000 images of larval zebrafish, with more than 1 500 of these being annotated. The 3D models can be manipulated on screen or virtually sectioned. This resource represents the first complete embryo to adult atlas for any species in 3D.

A Prospective Study of Left Atrial Spontaneous Echo Contrast and Thrombus in 100 Consecutive Patients Referred for Balloon Dilation of the Mitral Valve

The aim of this study was to determine the clinical, echocardiographic, and hemodynamic predictors of left atrial spontaneous echo contrast (SEC) and thrombus, respectively, in patients referred for balloon dilation of the mitral valve and to establish the relationship between the two phenomena in this group of patients. One hundred consecutive patients (mean age 57 +/- 14 years) referred for mitral balloon (Inoue) dilation were studied prospectively with transthoracic and transesophageal (83 biplane and 17 single plane) echocardiography (TEE) combined with spectral and color Doppler modalities, immediately before the procedure. TEE was repeated within 24 hours of valvotomy in the first 55 patients. All patients also underwent comprehensive left- and right-sided heart catheterization. TEE was performed successfully in 96 patients. SEC was detected in all 65 patients in atrial fibrillation and in 14 (45%) of 31 patients in sinus rhythm. Patients with SEC were significantly older (61 +/- 13 vs 45 +/- 12 years; p < 0.001) and had larger left atrial volume (98 +/- 48 vs 64 +/- 24 ml; p < 0.001), higher mitral valve echocardiographic scores (7.4 +/- 3.2 vs 5.3 +/- 2.6; p = 0.016), lower cardiac output (3.5 +/- 1.1 versus 4.6 +/- 0.9 L/min; p < 0.001), lower peak systolic pulmonary vein flow velocity (SVm) (24 +/- 12 versus 45 +/- 11 cm/sec; p < 0.001), and correspondingly lower systolic velocity-time integral (4.0 +/- 2.6 vs 7.9 +/- 2.9 cm; p < 0.001) than had patients without SEC. There were no significant associations between SEC and either mitral valve area or anticoagulant therapy. SVm and atrial fibrillation were found to be independent predictors of SEC. In patients in sinus rhythm, SVm was the only independent predictor of SEC. After mitral balloon dilation, SEC disappeared in only two of 35 patients in atrial fibrillation and in five of eight patients in sinus rhythm. Significant mitral regurgitation occurred in the two patients in atrial fibrillation. TEE detected left atrial thrombus in 14 patients. Thrombus was significantly associated with age, mitral valve area, and the severity of SEC. The latter was found to be an independent predictor of thrombus. Two patients in sinus rhythm had evidence of left atrial mechanical dysfunction. Both patients had left atrial SEC and one had thrombus in the appendage. It is concluded that SEC in patients with severe mitral stenosis is dependent on left atrial systolic function and peak systolic pulmonary vein velocity. It is not related to mitral valve area or anticoagulant therapy.(ABSTRACT TRUNCATED AT 400 WORDS)

Myotome meanderings. Cellular morphogenesis and the making of muscle.

The formation of muscles within the vertebrate embryo is a tightly orchestrated and complex undertaking. Beyond the initial specification of cells to become muscle are several complex cellular movements and migrations, which lead to the positioning of muscle precursors at specific locations within the embryo. The consequent differentiation, elongation and striation of these cells results in the formation of individual muscles. Investigation of the in vivo morphogenesis of individual vertebrate muscle cells has only recently begun, and is being approached through the use of sophisticated cell labelling and lineage analysis techniques. However, a consensus about the mechanisms involved has yet to be achieved. This review outlines vertebrate embryonic muscle formation in chick, fish and mice, focusing on the embryonic myotome, which generates both the axial musculature and the appendicular muscle of the fins and limbs. We highlight the points of consensus about, and the complexity of, this developmental system, and propose an evolutionary context for the basis of these understandings.

Isolation of three zebrafish dachshund homologues and their expression in sensory organs, the central nervous system and pectoral fin buds

Drosophila dachshund (dac) interacts with sine oculis (so), eyes absent (eya) and eyeless (ey) to control compound eye development. We have cloned three zebrafish dac homologues, dachA, dachB and dachC, which are expressed widely, in distinct but overlapping patterns. Expression of all three is found in sensory organs, the central nervous system and pectoral fin buds. dachA is also expressed strongly in the somites and dachC in the neural crest and pronephros. These expression domains overlap extensively with those of zebrafish pax, eya and six family members, the homologues of Drosophila ey, eya and so, respectively. This is consistent with the proposal that Dach, Eya, Six and Pax family members may form networks, similar to that found in the fly eye, in the development of many vertebrate organs.

Sequence Characterization of Teleost Fish Melanocortin Receptors

Abstract: Zebrafish are an excellent model system for studying the function of melanocortins in developmental and physiological processes, not least because there are a considerable number of mutant lines in which pigment patterns are affected. The behavior of fish melanophores is influenced by α‐melanocyte‐stimulating hormone (α‐MSH) and melanin‐concentrating hormone (MCH). We have used a rapid assay for α‐MSH and MCH function using melanophores present on single zebrafish scales. By in silico analysis, we have identified the full complement of melanocortin receptors in both zebrafish and the pufferfish, Fugu. Mammals have five such receptors. Zebrafish have six melanocortin receptors, including two MC5R orthologues, whereas Fugu, lacking MC3R, has only four. We have confirmed the sequences of these 10 genes and show the comparison of the amino acid sequences of the encoded proteins with the orthologous receptor in other vertebrates.

The comparative value of transesophageal and transthoracic echocardiography before and after percutaneous mitral balloon valvotomy: A prospective study

Transthoracic (TTE) and transesophageal echocardiography (TEE) were performed prospectively on 53 consecutive patients (mean age 59 +/- 14 years) immediately before and within 24 hours of mitral balloon valvotomy to compare the relative value of the two techniques. Biplane TEE was used in 38 patients and single-plane imaging was done in 11. All patients underwent left and right cardiac catheterization, left ventriculography, and coronary angiography. While TEE provided excellent images of the mitral valve in all patients, imaging planes were more limited than by TTE. Mitral valve morphology could be assessed satisfactorily by either technique. Echo scores derived from each showed good correlation (r = 0.90, p < 0.001). TEE transgastric longitudinal scanning provided superior detail of the subvalvar apparatus but only in 20 (53%) of 38 patients. Patients with good transgastric views had significantly smaller left atrial volumes than those without (58 +/- 22 vs 106 +/- 41 cm3, p < 0.001). Mitral valve orifice and the commissures were better assessed by TTE. Before valvotomy, mitral regurgitation (MR) graded by TEE and TTE color flow mapping was concordant with angiography in 80% and 81%, respectively. After valvotomy, TTE color flow mapping failed to detect MR in two of the three patients who developed severe MR. Two of these patients were examined by TEE, which demonstrated both the MR jets as well as leaflet tears. Thrombus was diagnosed in the left atrium in eight patients by TEE and in only one patient by TTE. Biplane TEE was required for accurate thrombus localization and for assessing its size and extent. Five patients with thrombus underwent balloon valvotomy without complications. Left-to-right atrial shunting was detected by TEE and TTE in 95% and 48% of patients, respectively. Flow convergence regions, from which quantitative flow information can be derived, were imaged by TEE only. TTE and TEE have complementary roles. However, TEE is essential for excluding thrombus in the left atrium before balloon valvotomy. After the procedure, TEE is recommended for the evaluation of patients with severe mitral regurgitation.

Zebrafish prox1b Mutants Develop a Lymphatic Vasculature, and prox1b Does Not Specifically Mark Lymphatic Endothelial Cells

Background The expression of the Prospero homeodomain transcription factor (Prox1) in a subset of cardinal venous cells specifies the lymphatic lineage in mice. Prox1 is also indispensible for the maintenance of lymphatic cell fate, and is therefore considered a master control gene for lymphangiogenesis in mammals. In zebrafish, there are two prox1 paralogues, the previously described prox1 (also known as prox1a) and the newly identified prox1b. Principal Findings To investigate the role of the prox1b gene in zebrafish lymphangiogenesis, we knocked-down prox1b and found that depletion of prox1b mRNA did not cause lymphatic defects. We also generated two different prox1b mutant alleles, and maternal-zygotic homozygous mutant embryos were viable and did not show any lymphatic defects. Furthermore, the expression of prox1b was not restricted to lymphatic vessels during zebrafish development. Conclusion We conclude that Prox1b activity is not essential for embryonic lymphatic development in zebrafish.

FishNet: An Interactive Database of Zebrafish Development

This chapter describes the major features of the website FishNet, which is an interactive database for zebrafish development. It discusses the pros and cons of each of the digital and print versions. The greatest advantage of the print version is its portable nature, allowing its use in the laboratory or aquarium where access to the Internet resource may not be possible or appropriate, and it is often easier to evaluate images in high-quality prints instead of display technology. However, the website has an edge over the print resource because the complete stage series and all sections within each sample embryo can be accessed through the website. The interactive nature of the website also allows the virtual sectioning of the 3D models at any of the represented stages and to zoom in and out to different image magnifications. It is also possible to view volume or surface renderings of the complete sample that may be manipulated on screen, which are particularly useful for mental conceptualization of anatomical morphology. The benefit of the dynamic nature of the website is the possibility for information to be easily updated, which allows both for addition of further annotations and any modification where necessary. Thus, the delivery of an anatomical resource via the Internet holds a number of advantages over a traditional, printed version.