Fin Development Research Articles

Thermally-induced phenotypic plasticity in gilthead seabream Sparus aurata L. (Perciformes, Sparidae)

Abstract Finfish present a great ability to modify their phenotype in response to environmental conditions especially in the early ontogenetic period. Such plastic phenotypic responses have a great importance, from both the ecological and aquaculture point of view. The present study examined the effect of water temperature on the ontogeny and juvenile phenotype of Sparus aurata L. Six combinations of three temperatures (16, 19, and 22 °C) were applied during different phases of ontogeny up to the juvenile stage (ca 33–37 mm standard length, SL). Elevated temperature resulted in a relative acceleration of differentiation versus growth, which morphologically was evident as a significantly smaller SL (ca 11% decrease) at different ontogenetic events (development of fins, squamation and body shape). Moreover, geometric morphometric analysis clearly showed a significant effect of water temperature during early ontogeny on the juvenile body-shape. Thermally-induced variation of juvenile body shape was mainly expressed across the first canonical axis (56.4% explained variance), which discriminated the groups of highest temperatures from the rest. Water temperature mainly affected the position of the bases of supraoccipital and of basioccipital bones, of the upper jaw, as well as of the dorsal, anal and pelvic fins. The results are discussed with respect to the potential use of thermal manipulations during the hatchery phase to control the phenotype of S. aurata at the end of on-growing phase, i.e. at commercial size.

Pelvic and reproductive structures in placoderms (stem gnathostomes).

Newly discovered pelvic and reproductive structures within placoderms, representing some of the most crownward members of the gnathostome stem group and the most basal jawed vertebrates, challenge established ideas on the origin of the pelvic girdle and reproductive complexity. Here we critically review previous descriptions of the pelvic structures in placoderms and reinterpret the morphology of the pelvic region within the arthrodires and ptyctodonts, in particular the position of the pelvic fin and the relationship of the male clasper to the pelvic girdle. Absence of clear articular surfaces on the clasper and girdle in the Arthrodira, along with evidence from the Ptyctodontida, suggest that these are separate structures along the body. We describe similarities between the pectoral and pelvic girdles and claspers, for example, all these have both dermal and perichondral (cartilaginous) components. Claspers in placoderms and chondrichthyans develop in very different ways; in sharks, claspers develop from the pelvic fin while the claspers in placoderms develop separately, suggesting that their independent development involved a posterior extension of the 'competent stripes' for fin development previously limited to the region between the paired pectoral and pelvic fins. Within this expanded zone, we suggest that clasper position relative to the pelvic fins was determined by genes responsible for limb position. Information on early gnathostome reproductive processes is preserved in both the Ptyctodontida and Arthrodira, including the presence of multiple embryos in pregnant females, embryos of differing sizes and of different sexes (e.g. male claspers preserved in some embyros). By comparison with chondrichthyans, these observations suggest more complex reproductive strategies in placoderms than previously appreciated.

The dlx5a/dlx6a genes play essential roles in the early development of zebrafish median fin and pectoral structures.

The Dlx5 and Dlx6 genes encode homeodomain transcription factors essential for the proper development of limbs in mammalian species. However, the role of their teleost counterparts in fin development has received little attention. Here, we show that dlx5a is an early marker of apical ectodermal cells of the pectoral fin buds and of the median fin fold, but also of cleithrum precursor cells during pectoral girdle development. We propose that early median fin fold establishment results from the medial convergence of dlx5a-expressing cells at the lateral edges of the neural keel. Expression analysis also shows involvement of dlx5a during appendage skeletogenesis. Using morpholino-mediated knock down, we demonstrate that disrupted dlx5a/6a function results in pectoral fin agenesis associated with misexpression of bmp4, fgf8a, and1 and msx genes. In contrast, the median fin fold presents defects in mesenchymal cell migration and actinotrichia formation, whereas the initial specification seems to occur normally. Our results demonstrate that the dlx5a/6a genes are essential for the induction of pectoral fin outgrowth, but are not required during median fin fold specification. The dlx5a/6a knock down also causes a failure of cleithrum formation associated with a drastic loss of runx2b and col10a1 expression. The data indicate distinct requirements for dlx5a/6a during median and pectoral fin development suggesting that initiation of unpaired and paired fin formation are not directed through the same molecular mechanisms. Our results refocus arguments on the mechanistic basis of paired appendage genesis during vertebrate evolution.

Distinct tissue-specific requirements for the zebrafish tbx5 genes during heart, retina and pectoral fin development.

The transcription factor Tbx5 is expressed in the developing heart, eyes and anterior appendages. Mutations in human TBX5 cause Holt–Oram syndrome, a condition characterized by heart and upper limb malformations. Tbx5-knockout mouse embryos have severely impaired forelimb and heart morphogenesis from the earliest stages of their development. However, zebrafish embryos with compromised tbx5 function show a complete absence of pectoral fins, while heart development is disturbed at significantly later developmental stages and eye development remains to be thoroughly analysed. We identified a novel tbx5 gene in zebrafish—tbx5b—that is co-expressed with its paralogue, tbx5a, in the developing eye and heart and hypothesized that functional redundancy could be occurring in these organs in embryos with impaired tbx5a function. We have now investigated the consequences of tbx5a and/or tbx5b downregulation in zebrafish to reveal that tbx5 genes have essential roles in the establishment of cardiac laterality, dorsoventral retina axis organization and pectoral fin development. Our data show that distinct relationships between tbx5 paralogues are required in a tissue-specific manner to ensure the proper morphogenesis of the three organs in which they are expressed. Furthermore, we uncover a novel role for tbx5 genes in the establishment of correct heart asymmetry in zebrafish embryos.

Toxicity Assessment of 7 Anticancer Compounds in Zebrafish

Toxicity is one of the major reasons for failure in drug development. Zebrafish, as an ideal vertebrate model, could also be used to evaluate drug toxicity. In this study, we aimed to show the predictability and highlight novel findings of toxicity in zebrafish model. Seven anticancer compounds, including triptolide (TP), gambogic acid (GA), mycophenolic acid (MPA), curcumin, auranofin, thalidomide, and taxol, were assessed in zebrafish for their toxicity. Three compounds (GA, TP, and taxol) showed highest acute lethality, with 50% lethal concentration ≈ 1 μmol/L. Missing tails, severe pericardial edema, and enlarged yolk sacs were observed in MPA-treated embryos. The development of pectoral fins was severely disturbed in thalidomide-, GA-, and TP-treated embryos. Bradycardia was observed in MPA- and thalidomide-treated groups. Our findings suggested that the zebrafish are a good model for toxicity assessment of anticancer compounds.

New frontiers in the evolution of fin development

The locomotory appendages of vertebrates have undergone significant changes during evolution, which likely promoted a wide range of adaptive strategies. These appendages first evolved as unpaired finfolds in the dorsal midline of early chordates, more than 500 million years ago. Later on, during vertebrates' radiation, two sets of locomotory appendages emerged, developing from both sides of the latero-ventral body wall. The morphology of these paired fins in fishes at different phylogenetic positions suggests an evolutionary tendency for increasing elaboration of the endoskeleton and concomitant reduction of the distal dermoskeleton. This evolutionary process culminated with the origin of limbs in the lineages leading to tetrapods. The developmental programs responsible for the evolution of vertebrate appendages have been a major topic for evolutionary developmental biology recently. Gene expression comparisons performed in chordates explored how these mechanisms were transferred from a midline to latero-ventral position. On another front, gene function assays have begun to test classical hypotheses concerning the transition from fish fins to tetrapod limbs. In this review, we highlight these recent findings on the evolution of vertebrate fin development. First, we discuss new perspectives on the transition from midline to paired appendages focus on (i) origin and molecular regionalization of the lateral plate mesoderm and (ii) novel ectodermic competency zones for fin induction. Next, we review recent work exploring how tetrapod limbs evolved from fish fins, considering (i) molecular and structural changes in the distal ectoderm of fins and (ii) modulation of 5'HoxD transcription during fin endoskeleton development.

A Footnote to the Evolution of Digits

A Footnote to the Evolution of Digits

Skeletal Development and Mineralization Pattern of the Vertebral Column, Dorsal, Anal and Caudal Fin Complex in Seriola Rivoliana (Valenciennes, 1833) Larvae

Bone and fins development in Seriola rivoliana were studied from cleared and stained specimens from 3 to 33 days after hatching. The vertebral column began to mineralize in the neural arches at 4.40 ± 0.14 mm Standard Length (SL), continued with the haemal arches and centrums following a cranial-caudal direction. Mineralization of the caudal fin structures started with the caudal rays by 5.12 ± 0.11 mm SL, at the same time that the notochord flexion occurs. The first dorsal and anal fin structures were the hard spines (S), and lepidotrichium (R) by 8.01 ± 0.26 mm SL. The metamorphosis was completed by 11.82 ± 0.4 mm SL. Finally, the fin supports (pterygiophores) and the caudal fins were completely mineralized by 16.1 ± 0.89 mm SL. In addition, the meristic data of 23 structures were provided. Results from the present study might be used as a practical guide for future studies on this field with S. rivoliana or in related species.

Loss of the Cytoskeletal Protein Pdlim7 Predisposes Mice to Heart Defects and Hemostatic Dysfunction

The actin-associated protein Pdlim7 is essential for heart and fin development in zebrafish; however, the expression and function of this PDZ-LIM family member in the mammal has remained unclear. Here, we show that Pdlim7 predominantly localizes to actin-rich structures in mice including the heart, vascular smooth muscle, and platelets. To test the requirement for Pdlim7 in mammalian development and function, we analyzed a mouse strain with global genetic inactivation of Pdlim7. We demonstrate that Pdlim7 loss-of-function leads to significant postnatal mortality. Inactivation of Pdlim7 does not disrupt cardiac development, but causes mild cardiac dysfunction in adult mice. Adult Pdlim7 -/- mice displayed increased mitral and tricuspid valve annulus to body weight ratios. These structural aberrations in Pdlim7 -/- mice were supported by three-dimensional reconstructions of adult cardiac valves, which revealed increased surface area to volume ratios for the mitral and tricuspid valve leaflets. Unexpectedly, we found that loss of Pdlim7 triggers systemic venous and arterial thrombosis, leading to significant mortality shortly after birth in Pdlim7 +/- (11/60) and Pdlim7 -/- (19/35) mice. In line with a prothrombotic phenotype, adult Pdlim7 -/- mice exhibit dramatically decreased tail bleed times compared to controls. These findings reveal a novel and unexpected function for Pdlim7 in maintaining proper hemostasis in neonatal and adult mice.

Developmental residue and developmental novelty - different modes of adipose-fin formation during ontogeny

The adipose fin is a structure with questionable function, for a long time even regarded as a rudimentary element without any function. A comparative study of adipose fin development revealed two different modes: a salmoniform-type where the adipose fin develops directly from the larval fin fold simultaneously with the other median fins. And a characiform-type where the adipose fin develops anew after the reduction of the larval fin fold. Compared to the first mode the latter starts late in ontogeny, when all other median fins already have their shape, fin rays and colouration. The characiform-type of adipose fin development contradicts the view that this structure is just a larval fin fold remainder. It also disputes the hypothesis of the adipose fin as a structure without any function. Such a hypothesis cannot explain a systematically widely distributed structure which even exhibits different modes of ontogenetic development in different taxa. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Notch Signalling Is Required for the Formation of Structurally Stable Muscle Fibres in Zebrafish

BackgroundAccurate regulation of Notch signalling is central for developmental processes in a variety of tissues, but its function in pectoral fin development in zebrafish is still unknown.Methodology/Principal FindingsHere we show that core elements necessary for a functional Notch pathway are expressed in developing pectoral fins in or near prospective muscle territories. Blocking Notch signalling at different levels of the pathway consistently leads to the formation of thin, wavy, fragmented and mechanically weak muscles fibres and loss of stress fibres in endoskeletal disc cells in pectoral fins. Although the structural muscle genes encoding Desmin and Vinculin are normally transcribed in Notch-disrupted pectoral fins, their proteins levels are severely reduced, suggesting that weak mechanical forces produced by the muscle fibres are unable to stabilize/localize these proteins. Moreover, in Notch signalling disrupted pectoral fins there is a decrease in the number of Pax7-positive cells indicative of a defect in myogenesis.Conclusions/SignificanceWe propose that by controlling the differentiation of myogenic progenitor cells, Notch signalling might secure the formation of structurally stable muscle fibres in the zebrafish pectoral fin.

A Three-Dimensional Kinematics Analysis of a Koi Carp Pectoral Fin by Digital Image Processing

Pectoral fins fascinate researchers for their important role in fish maneuvers. By possessing a complicated flexible structure with several fin rays made by a thin film, the fin exhibits a three-dimensional (3D) motion. The complex 3D fin kinematics makes it challenging to study the performance of pectoral fin. Nevertheless, a detailed study on the 3D motion pattern of pectoral fins is necessary to the design and control of a bio-inspired fin rays. Therefore, a highspeed photography system is introduced in this paper to study the 3D motion of a Koi Carp by analyzing the two views of its pectoral fin simultaneously. The key motions of the pectoral fins are first captured in both hovering and retreating. Next, the 3D configuration of the pectoral fins is reconstructed by digital image processing, in which the movement of fin rays during fish retreating and hovering is obtained. Furthermore, the method of Singular Value Decomposition (SVD) is adopted to extract the basic motion patterns of pectoral fins from extensive image sequences, i.e. expansion, bending, cupping, and undulation. It is believed that the movement of the fin rays and the basic patterns of the pectoral fins obtained in the present work can provide a good foundation for the development and control of bionic flexible pectoral fins for underwater propeller.

The African coelacanth genome provides insights into tetrapod evolution

It was a zoological sensation when a living specimen of the coelacanth was first discovered in 1938, as this lineage of lobe-finned fish was thought to have gone extinct 70 million years ago. The modern coelacanth looks remarkably similar to many of its ancient relatives, and its evolutionary proximity to our own fish ancestors provides a glimpse of the fish that first walked on land. Here we report the genome sequence of the African coelacanth, Latimeria chalumnae. Through a phylogenomic analysis, we conclude that the lungfish, and not the coelacanth, is the closest living relative of tetrapods. Coelacanth protein-coding genes are significantly more slowly evolving than those of tetrapods, unlike other genomic features . Analyses of changes in genes and regulatory elements during the vertebrate adaptation to land highlight genes involved in immunity, nitrogen excretion and the development of fins, tail, ear, eye, brain, and olfaction. Functional assays of enhancers involved in the fin-to-limb transition and in the emergence of extra-embryonic tissues demonstrate the importance of the coelacanth genome as a blueprint for understanding tetrapod evolution.

Zebrafishtbx5paralogs demonstrate independent essential requirements in cardiac and pectoral fin development

T-box genes constitute a large family of transcriptional regulators involved in developmental patterning. Homozygous mutation of tbx5 leads to embryonic lethal cardiac phenotypes and forelimb malformations in vertebrate models. Haploinsufficiency of tbx5 results in Holt-Oram syndrome, a human congenital disease characterized by cardiac and forelimb defects. Homozygous mutation of zebrafish tbx5a leads to lethal defects in cardiac looping morphogenesis, blocks pectoral fin initiation, and impairs outgrowth. Recently, a second zebrafish tbx5 gene was described, termed tbx5b. Our phylogenetic analyses confirm tbx5b as a paralog that likely arose in the teleost-specific whole genome duplication ∼270 MYA. Using morpholino depletion studies, we find that tbx5b is required in the heart for embryonic survival, and influences the timing and morphogenesis of pectoral fin development. Because tbx5a hypomorphic mutations are embryonic lethal, tbx5a and tbx5b functions in the heart must not be completely redundant. Consistent with this hypothesis, simultaneous depletion of both tbx5 paralogs did not lead to more severe phenotypes, and injection of wild-type mRNA from one tbx5 paralog was not sufficient to cross-rescue phenotypes of the paralogous gene. Collectively, these data indicate that, despite similar spatio-temporal expression patterns, tbx5a and tbx5b have independent functions in heart and fin development.

Hoxd13 Contribution to the Evolution of Vertebrate Appendages

Fossil data suggest that limbs evolved from fish fins by sequential elaboration of their distal endoskeleton, giving rise to the autopod close to the tetrapod origin. This elaboration may have occurred by a simultaneous reduction of the distal ectodermal fold of fish fins. Modulation of 5'Hoxd gene transcription, through tetrapod-specific digit enhancers, has been suggested as a possible evolutionary mechanism involved in these morphological transformations. Here, we overexpress hoxd13a in zebrafish to investigate the impact of increasing 5'Hoxd expression during fin development. This overexpression causes increased proliferation, distal expansion of chondrogenic tissue and finfold reduction. In addition, we also show that the tetrapod-specific 5'Hoxd enhancer CsC promotes similar expression in zebrafish fins and mouse limbs. Our results support the idea that modulation of 5'Hoxd gene expression, by acquisition of novel enhancer elements, offered the substrate for the evolution of fins and the origin of tetrapod limbs.

The evolutionary history of the development of the pelvic fin/hindlimb.

The arms and legs of man are evolutionarily derived from the paired fins of primitive jawed fish. Few evolutionary changes have attracted as much attention as the origin of tetrapod limbs from the paired fins of ancestral fish. The hindlimbs of tetrapods are derived from the pelvic fins of ancestral fish. These evolutionary origins can be seen in the examination of shared gene and protein expression patterns during the development of pelvic fins and tetrapod hindlimbs. The pelvic fins of fish express key limb positioning, limb bud induction and limb outgrowth genes in a similar manner to that seen in hindlimb development of higher vertebrates. We are now at a point where many of the key players in the development of pelvic fins and vertebrate hindlimbs have been identified and we can now readily examine and compare mechanisms between species. This is yielding fascinating insights into how the developmental programme has altered during evolution and how that relates to anatomical change. The role of pelvic fins has also drastically changed over evolutionary history, from playing a minor role during swimming to developing into robust weight-bearing limbs. In addition, the pelvic fins/hindlimbs have been lost repeatedly in diverse species over evolutionary time. Here we review the evolution of pelvic fins and hindlimbs within the context of the changes in anatomical structure and the molecular mechanisms involved.

Mechanism of pectoral fin outgrowth in zebrafish development

Fins and limbs, which are considered to be homologous paired vertebrate appendages, have obvious morphological differences that arise during development. One major difference in their development is that the AER (apical ectodermal ridge), which organizes fin/limb development, transitions into a different, elongated organizing structure in the fin bud, the AF (apical fold). Although the role of AER in limb development has been clarified in many studies, little is known about the role of AF in fin development. Here, we investigated AF-driven morphogenesis in the pectoral fin of zebrafish. After the AER-AF transition at ∼36 hours post-fertilization, the AF was identifiable distal to the circumferential blood vessel of the fin bud. Moreover, the AF was divisible into two regions: the proximal AF (pAF) and the distal AF (dAF). Removing the AF caused the AER and a new AF to re-form. Interestingly, repeatedly removing the AF led to excessive elongation of the fin mesenchyme, suggesting that prolonged exposure to AER signals results in elongation of mesenchyme region for endoskeleton. Removal of the dAF affected outgrowth of the pAF region, suggesting that dAF signals act on the pAF. We also found that the elongation of the AF was caused by morphological changes in ectodermal cells. Our results suggest that the timing of the AER-AF transition mediates the differences between fins and limbs, and that the acquisition of a mechanism to maintain the AER was a crucial evolutionary step in the development of tetrapod limbs.

The Polycomb group protein Ring1b is essential for pectoral fin development

Polycomb group (PcG) proteins are transcriptional repressors that mediate epigenetic gene silencing by chromatin modification. PcG-mediated gene repression is implicated in development, cell differentiation, stem-cell fate maintenance and cancer. However, analysis of the roles of PcG proteins in orchestrating vertebrate developmental programs in vivo has been hampered by the early embryonic lethality of several PcG gene knockouts in mice. Here, we demonstrate that zebrafish Ring1b, the E3 ligase in Polycomb Repressive Complex 1 (PRC1), is essential for pectoral fin development. We show that differentiation of lateral plate mesoderm (LPM) cells into presumptive pectoral fin precursors is initiated normally in ring1b mutants, but fin bud outgrowth is impaired. Fgf signaling, which is essential for migration, proliferation and cell-fate maintenance during fin development, is not sufficiently activated in ring1b mutants. Exogenous application of FGF4, as well as enhanced stimulation of Fgf signaling by overactivated Wnt signaling in apc mutants, partially restores the fin developmental program. These results reveal that, in the absence of functional Ring1b, fin bud cells fail to execute the pectoral fin developmental program. Together, our results demonstrate that PcG-mediated gene regulation is essential for sustained Fgf signaling in vertebrate limb development.

Biology and culture of the clown loachChromobotia macracanthus(Cypriniformes, Cobitidae) : 3- Ontogeny, ecological and aquacultural implications

Hatchlings of clown loach (3.8 mm in total length, TL ) are pelagic. When reared at 26−28 °C, they become benthic 3 days after hatching (dah), when their swim bladder is inflated. The fin development sequence (pectorals , but the finfold persists until 25 − 26 mm TL (start of juvenile stage). Melanophores appear at 3 dah, they form a 5-bar pattern at 5 dah, then two bars (III and V) vanish progressively, producing at 26 mm TL the 3-bar pattern that is typical of adults. Throughout the ontogeny, the pigment pattern exhibits a structural regularity (bars spaced at regular intervals), which is interpreted in a functional perspective by reference to the maintaining of crypsis and signalling throughout. Exogenous feeding commences at 4 dah (5.5 mm TL ). Food intake (FI ) increases rapidly, from 6% wet body mass (WM ) at 5.5 mm TL to >20% WM in fish > 7 mm TL . Gut evacuation rate (R g ) increases with increasing meal size and fish size, as a result of gut coiling (from 8 to 15 mm TL ), and is highest at 11 mm TL (about 10% WM h-1 in fish feeding maximally). The allometric increase of FI and R g during the early larval stages is accompanied by increasing capacities for growth, so early sizes differences amplify rapidly during the ontogeny. Nevertheless, growth remains slow (mean of 0.4 mm TL day-1 from 4 to 29 dah; 0.9 mm TL day-1 for top growers). By contrast, unfed fish display long resistance to starvation (until 14−15 dah). The combination of slow growth and long resistance to starvation is discussed in respect to the reproductive phenology of the species, as the capacity of making metabolic economies prevails over fast growth for seasonal strategists spawning mainly at the start of the rainy season.

The making of differences between fins and limbs

'Evo-devo', an interdisciplinary field based on developmental biology, includes studies on the evolutionary processes leading to organ morphologies and functions. One fascinating theme in evo-devo is how fish fins evolved into tetrapod limbs. Studies by many scientists, including geneticists, mathematical biologists, and paleontologists, have led to the idea that fins and limbs are homologous organs; now it is the job of developmental biologists to integrate these data into a reliable scenario for the mechanism of fin-to-limb evolution. Here, we describe the fin-to-limb transition based on key recent developmental studies from various research fields that describe mechanisms that may underlie the development of fins, limb-like fins, and limbs.