Paul Eckhard Witten

• Professor at Ghent University

The ubiquitin-binding protein p62, encoded by Sequestosome 1 (SQSTM1), is an essential molecular adaptor for selective autophagy. Heterozygous mutations deleting or disrupting the ubiquitin-associated (UBA) domain of p62 have been reported as the major genetic cause for Paget’s disease of bone (PDB), the second most common skeletal disease, charact...

Atlantic salmon is an important aquaculture species that has fascinated naturalists for centuries, resulting in its biology being widely characterized. Certain details about the early development and the inheritance of meristic variation in the post‐cranial axial skeleton are, however, largely unexplored. The present study gives a detailed descript...

Background While adult mammals are unable to grow new nephrons, cartilaginous fish kidneys display nephrogenesis throughout life. In this study, we investigated the molecular properties of nephron progenitor cells (NPCs) within the kidney of the catshark ( Scyliorhinus canicula ). Methods We used branched DNA (bDNA) in situ hybridization to analyz...

Rare monogenic disorders often exhibit significant phenotypic variability among individuals sharing identical genetic mutations. Bruck syndrome (BS), a prime example, is characterized by bone fragility and congenital contractures, although with a pronounced variability among family members. BS arises from recessive biallelic mutations in FKBP10 or...

Zebrafish and other small laboratory fishes are emerging as important animal models for investigating human skeletal development and diseases. In recent years, there has been a notable increase in research publications employing x-ray radiography and micro-computed tomography to analyze the skeletal structures of these animals. However, evaluating...

Current procedures to establish vertebral column regionalization (e.g., histology) in fish are time consuming and difficult to apply. The aim of this study was to develop a more rapid and accurate radiology‐based method for Atlantic salmon (Salmo salar). A detailed analysis of 90 animals (4 kg) led to the establishment of region‐specific radiograph...

A healthy skeletal system is fundamental to fish welfare and performance and a key physiological feature of a robust fish. The presence of skeletal deformities in farmed salmonids is a persistent welfare problem in aquaculture, and one which threatens to impede industry growth. Deformities of the fine bones of fish, such as ribs and intermuscular b...

Bone matrix formation and mineralization are two closely related, yet separated processes. Matrix formation occurs first, mineralization is a second step strictly dependent on the dietary intake of calcium and phosphorus (P). However, mineralization is commonly used as diagnostic parameter for bone-related diseases. In this context, bone loss, ofte...

Most tooth‐bearing non‐mammalian vertebrates have the capacity to replace their teeth throughout life. This capacity was lost in mammals, which replace their teeth only once at most. Not surprisingly, continuous tooth replacement has attracted much attention. Classical morphological studies (e.g. to analyse patterns of replacement) are now being co...

DAF-FM DA is widely used as a live staining compound to show the presence of nitric oxide (NO) in cells. Applying this stain to live zebrafish embryos is known to indicate early centers of bone formation, but the precise (cellular) location of the signal has hitherto not been revealed. Using sections of zebrafish embryos live-stained with DAF-FM DA...

ABSTRACT Teeth are defined as internal odontodes, sharing a common ancestry with skin denticles (external odontodes). The conquest of the oropharynx by odontodes, originally limited to the body surface, is now commonly accepted (the ‘outside in’ theory on tooth origins). Yet, an unanswered question is how external epithelia could have transferred...

Land-based aquaculture systems can have an elevated content of metabolically-derived carbon dioxide (CO2) in the water. Interestingly elevated CO2 levels have been suggested to induce nephrocalcinosis and to increase the bone mineral content. This raises the question if dietary phosphorus (P), one of the main components of bone minerals, can be red...

Vertebral bodies are composed of two types of metameric elements, centra and arches, each of which is considered as a developmental module. Most parts of the teleost vertebral column have a one-to-one relationship between centra and arches, although, in all teleosts, this one-to-one relationship is lost in the caudal fin endoskeleton. Deviation fro...

Expansion of land-based systems in fish farms elevate the content of metabolic carbon dioxide (CO2) in the water. High CO2 is suggested to increase the bone mineral content in Atlantic salmon (Salmo salar, L.). Conversely, low dietary phosphorus (P) halts bone mineralization. This study examines if high CO2 can counteract reduced bone mineralizatio...

Synopsis Monitoring the physiology of small aquatic and marine teleost fish presents challenges. Blood samples, often the first choice for endocrinologists, can be difficult or even impossible to obtain and alternative matrices currently used for hormone analyses do not occur in fishes (e.g., hair, feathers etc.) or are not easily collected from sm...

Introduction Trimeric intracellular potassium channels TRIC-A and -B are endoplasmic reticulum (ER) integral membrane proteins, involved in the regulation of calcium release mediated by ryanodine (RyRs) and inositol 1,4,5-trisphosphate (IP3Rs) receptors, respectively. While TRIC-A is mainly expressed in excitable cells, TRIC-B is ubiquitously distr...

Haemal lordosis, a frequent skeletal deformity in teleost fish, has long been correlated with increased mechanical loads induced by swimming activity. In the present study, we examine whether juvenile zebrafish can recover from haemal lordosis and explore the musculoskeletal mechanisms involved. Juveniles were subjected to a swimming challenge test...

Introduction Hyper-radiodense vertebrae (HDV) are a frequently radiologically diagnosed deformity in Atlantic salmon Salmo salar, L. (Helland et al., 2006; Fraser et al., 2019; Sambraus et al., 2020). Increased radiodensity is caused by ectopic cartilage replacing adipose tissue in bone marrow spaces. In some cases, there are bent bone trabeculae d...

PURPOSE Phosphorus (P) is critical for bone matrix mineralisation. Chronic P-deficiency causes severe bone malformations in humans and other vertebrates. A series of studies on Atlantic salmon examines the effect of periodic P-deficiency and P-oversupply on bone and the potential to recover from P-deficiency (1-4). METHODS Salmo salar received th...

The main minerals of bone are calcium and phosphorus. While teleost can obtain calcium in suffcient amounts from water they depend on dietary P supply. Dietary P defciency is considered a risk factor for the development of vertebral deformities in farmed Atlantic salmon (Salmo salar). In commercial diet formulations dietary P requirements are met b...

Intermuscular bones (IBs) are mineralized spicules, present in the myosepta of many, but not all teleost species. IBs are often small and sharp, and they consequently limit how the fish can be processed, cause injury or trauma if lodged in consumers' throat or mouth and therefore affect the appeal of the fish to many consumers. The development of I...

Oryzias latipes is increasingly used as a model in biomedical skeletal research. The standard approach is to generate genetic variants with particular skeletal phenotypes which resemble skeletal diseases in humans. The proper diagnosis of skeletal variation is key for this type of research. However, even laboratory rearing conditions can alter skel...

Vertebral deformities can impair health, welfare, and product quality in farmed Atlantic salmon. Deformities detected early in the production cycle raise questions about their further development: which types of deformities will progress and which types of deformities will worsen over time? To study this, Atlantic salmon parr (start experimental fe...

266pp 53 illustrations ------- The notochord is the organ that defines our phylum. It is our first axial skeleton and much more than an embryonic placeholder. Active lifelong in most vertebrates and decisive for development and evolution of the vertebral column this book gives the attention to the notochord it deserves, discussing its development, e...

Osteogenesis imperfecta (OI) is a group of heritable disorders affecting bone and other connective tissues. Dominant OI forms are mainly caused by mutations in collagen type I. Patients suffer from skeletal deformities, fractures of long bones and vertebral compression fractures from early childhood onward. Altered collagen structure and excess min...

In the era of molecular biology, identification of cells and even tissues mostly relies on the presence of fluorescent tags, or of "marker gene" expression. We list a number of caveats and present a protocol for embedding, sectioning, and staining semithin plastic sections. The method is neither new nor innovative, but is meant to revive skills tha...

Back pain is a common condition with a high social impact and represents a global health burden. Intervertebral disc disease (IVDD) is one of the major causes of back pain; no therapeutics are currently available to reverse this disease. The impact of bone mineral density (BMD) on IVDD has been controversial, with some studies suggesting osteoporos...

There are several competing hypotheses on tooth origins, with discussions eventually settling in favour of an 'outside-in' scenario, in which internal odontodes (teeth) derived from external odontodes (skin denticles) in jawless vertebrates. The evolution of oral teeth from skin denticles can be intuitively understood from their location at the mou...

Bone-producing osteoblasts and dentin-producing odontoblasts are closely related cell types, a result from their shared evolutionary history in the ancient dermal skeleton. In mammals, the two cell types can be distinguished based on histological characters and the cells’ position in the pulp cavity or in the tripartite periodontal complex. Differe...

The iconic phenotype of seadragons includes leaf-like appendages, a toothless tubular mouth, and male pregnancy involving incubation of fertilized eggs on an open “brood patch.” We de novo–sequenced male and female genomes of the common seadragon ( Phyllopteryx taeniolatus ) and its closely related species, the alligator pipefish ( Syngnathoides bi...

This current experiment focuses on freshwater stages (parr) aiming to analyse the effect of low and high phosphorus diet on i) bone formation and bone mineralisation, ii) shape and structure of vertebral bodies, and iii) occurrence of skeletal deformities. This study indicates that a diet low in P alone is not responsible for the development of v...

Gilthead seabream (Sparus aurata Linnaeus, 1758 (Perciformes, Sparidae)) is an important aquaculture species in the Mediterranean Sea basin. Yet, quantitative data on its dentition under standard farming conditions are currently lacking. Furthermore, it is unknown if the dentition can adapt to food of different sizes. Here, we describe the lower ja...

Deficiency in dietary phosphorus (P) is considered as a nutritional risk factor for the development of vertebral column deformities in farmed Atlantic salmon Salmo salar, L. This mono-factorial study examines how 11-week deficiency and excess of dietary P influence the structure and microstructure of the vertebral bodies in juvenile, freshwater sta...

Oryzias latipes is increasingly used as model for human bone diseases. The variability of skeletal elements under laboratory conditions is an important component of diagnosing mutant phenotypes. Our knowledge about type and extent of skeletal variations in this species is scarce, particularly related to rearing density. Aims are (I) to provide a co...

Dietary phosphorus (P) is essential for bone mineralisation in vertebrates. P deficiency can cause growth retardation, osteomalacia and bone deformities, both in teleosts and in mammals. Conversely, excess P supply can trigger soft tissue calcification and bone hypermineralisation. This study uses a wide range of complementary techniques (X-rays, h...

Supplementary material. Cotti, S.; Huysseune, A.; Koppe, W.; Rücklin, M.; Marone, F.; Wölfel, E.M.; Fiedler, I.A.K.; Busse, B.; Forlino, A.; Witten, P.E. More Bone with Less Minerals? The Effects of Dietary Phosphorus on the Post-Cranial Skeleton in Zebrafish. Int. J. Mol. Sci. 2020, 21, 5429, https://doi.org/10.3390/ijms21155429

Significance Many vertebrates possess teeth deep in the pharynx. While teeth are known to derive from odontodes (skin denticles), it is unknown if an external epithelium is still required to produce a pharyngeal tooth, such as for odontode formation. Here, we show that the epithelial enamel organ of pharyngeal teeth in zebrafish is formed from endo...

One of the most frequently applied techniques in zebrafish (Danio rerio) research is the visualisation or manipulation of specific cell populations using transgenic reporter lines. The generation of these transgenic zebrafish, displaying cell‐ or tissue‐specific expression of frequently used fluorophores such as Green Fluorescent Protein (GFP) or m...

Prolyl 3-hydroxylation is a rare collagen type I post translational modification in fibrillar collagens. The primary 3Hyp substrate sites in type I collagen are targeted by an endoplasmic reticulum (ER) complex composed by cartilage associated protein (CRTAP), prolyl 3-hydroxylase 1 (P3H1) and prolyl cis/trans isomerase B, whose mutations cause rec...

The teleost zebrafish (Danio rerio), an established model for human skeletal diseases, is reared under controlled conditions with defined parameters for temperature and photoperiod. Studies aimed at defining the proper rearing density have been performed with regard to behavioural and physiological stress response, sex ratio and reproduction. Studi...

The anabolic effect of exercise on muscles and bones is well documented. In teleost fish, exercise has been shown to accelerate skeletogenesis, to increase bone volume, and to change the shape of vertebral bodies. Still, increased swimming has also been reported to induce malformations of the teleost vertebral column, particularly lordosis. This st...

Modern altricial birds are the fastest growing vertebrates, whereas various degrees of precocity (functional maturity) result in slower growth. Diaphyseal osteohistology, the best proxy for inferring relative growth rates in fossils, suggests that in the earliest birds, posthatching growth rates were more variable than in modern representatives, wi...

The gnathostome pharyngeal cavity functions in food transport and respiration. In amniotes the mouth and nares are the only channels allowing direct contact between internal and external epithelia. In teleost fish, gill slits arise through opening of endodermal pouches and connect the pharynx to the exterior. Using transgenic zebrafish lines, cell...

In this study, we describe an abnormal ectopically mineralized s tructure (EMS) thatwas found inside the skull of a juvenile Sparus aurata that also showed a bilateral opercular deformation. The overall phenotype and tissue composition were studied using micro‐CT scanning and histological analyses. The ectopic structure occupies a large volume of t...

In this study, we describe an abnormal ectopically mineralized structure (EMS) that was found inside the skull of a juvenile Sparus aurata that also showed a bilateral opercular deformation. The overall phenotype and tissue composition were studied using micro‐CT scanning and histological analyses. The ectopic structure occupies a large volume of t...

As a corollary to the ‘modified outside in’ hypothesis about the evolu-tionary origin of vertebrate teeth (Huysseune et al., 2009, J. Anat.214: 465-476), we previously hypothesized that the development of,allegedly endoderm-derived, pharyngeal teeth in teleost fish requiresectodermal contribution or signaling. This may have been facilitatedby ectod...

The gnathostome pharyngeal cavity functions in food transport andrespiration. In amniotes the mouth and nares are the only channels all-owing direct contact between internal and external epithelia. In teleostfish, gill slits arise through opening of endodermal pouches and connectthe pharynx to the exterior. Using zebrafish (Danio rerio) as a model,...

Bone health is important for a viable and ethically sound Atlantic salmon aquaculture industry. Two important risk factors for vertebral deformities are dietary phosphorus and water temperature. Here, we explore the interplay between these two factors during a full production of Atlantic salmon. Salmon were fed one of three diets (low 4.4–5.0 g/kg,...

Zebrafish is now widely used in biomedical research as a model for human diseases, but the relevance of the model depends on a rigorous analysis of the phenotypes obtained. Many zebrafish disease models, experimental techniques and manipulations take advantage of fluorescent reporter molecules. However, phenotypic analysis often does not go beyond...

Significance Body reorganization in eels during gametogenesis can induce undesired side effects with possible pathological significance. This study provides analytical evidence for the maternal transfer of toxic metals from soft and hard tissues to the ovaries of mature females. By illustrating the metabolic fluxes and fate of mobilized minerals an...

Evolution and Development of Fishes - edited by Zerina Johanson January 2019

Calcium and phosphorus (P) are the main bone minerals and P-deficiency causes hypomineralized bones (osteomalacia) and malformations. This study uses a P-deficient salmon model to falsify three hypotheses. First, an extended period of dietary P-deficiency does not cause pathologies other than osteomalacia. Second, secondary mineralization of non-mi...

Variation of vertebral centra numbers is common in vertebrates. Likewise, the number of associated elements such as ribs and neural and haemal arches can vary and affect all regions of the vertebral column. In mammals, only the number of cervical vertebrae is invariable. Variation of total vertebral centra numbers is well documented in teleost fish...

Caudal‐fin lepidotrichia is composed of numerous segments, which are linked to each other by intersegmental joints. During fish growth, lepidotrichia elongate by the addition of new segments at their distal margin, whereas the length of each segment remains constant after it is formed. In the present paper, we examined whether the water temperature...

Significance Type I collagenopathies are a heterogenous group of connective tissue disorders, caused by genetic defects in type I collagen. Inherent to these disorders is a large clinical variability, of which the underlying molecular basis remains undefined. By systematically analyzing skeletal phenotypes in a large set of type I collagen zebrafis...

Teeth continue to be in the focus in many paleontological and neontological disciplines, and their morphological characters, histological structure and mode of attachment are the subject of ongoing studies. In this review, we elaborate on tooth shape. We first highlight the progress that was made over the last two decades in understanding the mecha...

Heterochrony, which is a change in the developmental rate and timing, is one of the mechanisms proposed to explain alterations in meristic characters, such as the variation in the numbers of skeletal elements between individuals within a population. To verify the possible role of heterochrony in the evolutionary transformation of the cyprinid phary...

Exercise promotes gain in bone mass through adaptive responses of the vertebrate skeleton. This mechanism counteracts age- and disease-related skeletal degradation, but remains to be fully understood. In life sciences, zebrafish emerged as a vertebrate model that can provide new insights into the complex mechanisms governing bone quality. To test t...

The capacity to fully replace teeth continuously makes zebrafish an attractive model to explore regeneration and tooth development. The requirement of attachment bone for the appearance of replacement teeth has been hypothesized but not yet investigated. The transcription factor sp7 ( osterix ) is known in mammals to play an important role during o...

The capacity to fully replace teeth continuously makes zebrafish an attractive model to explore regeneration and tooth development. The requirement of attachment bone for the appearance of replacement teeth has been hypothesized but not yet investigated. The transcription factor sp7 (osterix) is known in mammals to play an important role during odo...

Skeletal anomalies in reared european fish larvae and juveniles. Part 1: Normal and anomalous skeletogenic processes

Skeletal anomalies in reared european fish larvae and juveniles. Part 2: Main typologies, occurences and causative factors

Skeletal deformities in farmed fish are a recurrent problem. External malformations are easily recognized, but there is little information on how external malformations relate to malformations of the axial skeleton: the external phenotype–skeleton link. Here, this link is studied in post-hatch to first-feed life stages of Chinook salmon (Oncorhynch...

Teleost vertebral centra are often similar in size and shape, but vertebral-associated elements, i.e. neural arches, haemal arches and ribs, show regional differences. Here we examine how the presence, absence and specific anatomical and histological characters of vertebral centra-associated elements can be used to define vertebral column regions i...

This study is the first to describe the ultrastructural morphology of the envelope of Solea solea eggs from fertilisation until hatching. Defining the ultrastructural morphology of fish eggs is important for species identification and may assist in predicting the effect of external influences on these early life stages. In first instance, various f...

Nonmammalian vertebrates have the capacity of lifelong tooth replacement. In all vertebrates, tooth formation requires contact and interaction between the oral or pharyngeal epithelium and the underlying mesenchyme. To secure lifelong replacement, the presence of odontogenic stem cells has been postulated, particularly in the epithelial compartment...