Inadequate Dietary Phosphorus Levels Cause Skeletal Anomalies and Alter Osteocalcin Gene Expression in Zebrafish

Early manifestation of hypophosphatemic rickets in goslings: a potential role of insufficient muscular adenosine triphosphate in motility impairment of early P-deficient geese

We aimed to determine the onset time of hypophosphatemic rickets and investigate the mechanism of motility impairment through adenosine triphosphate (ATP) production in goslings. Two hundred and sixteen 1-day-old male Jiangnan white geese were randomly divided into 3 groups, with 6 replicates and 12 geese per replicate. Birds were fed on 3 diets: a control diet (nonphytic phosphorus, NPP, 0.38%), a P-deficient diet (PD; NPP, 0.08%), and a high P diet (HP; NPP, 0.80%) for 14 d. Subsequently, all birds were shifted to the control diet for an additional 14 d. The cumulative incidence of lameness increased significantly (P < 0.01) starting on d 4, reaching over 80% on d 7 and 100% on d 12 in the PD group. Drinking and eating frequency decreased from d 4 and d 5, respectively, in the PD group compared to the other groups (most P < 0.01). The PD group exhibited shorter and narrower beaks, higher (worse) curvature scores of the beak and costochondral junctions, swelling caput costae, and dirtier feathers since d 4, in contrast to the control and HP groups (most P < 0.01). The HP had bigger (P < 0.05) beak and sternum sizes than the control groups on d 4 to 11. Leg muscle ATP levels were lower (P < 0.01 or 0.05) on d 4 to 11; in contrast, adenosine diphosphate (d 7-11) was higher in PD compared to the control (P < 0.05). Leg muscle ATP level had positive linear (R2 > 0.40) correlations (r > 0.60) with eating and drinking frequencies on d 7 and 11 (P < 0.01). Bone stiffness, feather cleanliness, and ATP levels recovered (P > 0.05) to the control level, whereas bone size did not recover (P < 0.05) in PD and HP after eating the control diet for 2 wk. The onset time of hypophosphatemic rickets was around 4 d in goslings, and insufficient leg muscle ATP was related to the impaired motility observed in early P-deficient geese.

Evaluation of Post-Larval Diets for Indoor Weaned Largemouth Bass (Micropterus salmoides)

This study aimed to evaluate different commercial diets (Otohime C1, Aller Futura (AF), Biomar Inicio Plus (BIP)) and one experimental feed (EF) in terms of their effectiveness as post-larval diets for indoor weaned largemouth bass, LMB (Micropterus salmoides). Key variations in the content of nutritive values were monounsaturated fatty acid (MUFA) and highly unsaturated FA (HUFA) ω3. Fish were fed with one of four tested diets from the 33rd to the 40th day post-hatch (DPH). Biometric indices, digestive enzyme-specific activities, thyroid hormone status, and mRNA expression of genes coding for skeleton, neuron, and muscle growth were analyzed. The lowest skeletal deformity rate and highest survival among the treatments were seen in BIP-fed fish. Dietary lipids, with an appropriate balance between MUFA and polyunsaturated FA (PUFA), alongside amino acid balance, were shown to be the main contributors to the growth of the skeleton and/or fish survival. On the other hand, fish growth is correlated with fish digestive capacity and feed moisture percent rather than feed quality. Unexpectedly, BIP-fed fish were attributed with the lowest expression of skeleton differentiation markers, which may reflect the sacrifice of scale and/or cranium growth at the expense of somatic growth. This study highlights the role of non-marine ingredients in the nutrition of post-larval LMB.

The role of starter diets in the development of skeletal abnormalities in zebrafish Danio rerio (Hamilton, 1822)

Fish skeletal development has long been correlated with nutritional factors. Lack of zebrafish nutritional standardization, especially during the early stages, decreases the reproducibility of the conducted research. The present study represents an evaluation of four commercial (A, D, zebrafish specific; B, generic for freshwater larvae; C, specific for marine fish larvae) and one experimental (Ctrl) early diets on zebrafish skeletal development. Skeletal abnormalities rates in the different experimental groups were assessed at the end of the larval period (20 days post-fertilization, dpf) and after a swimming challenge test (SCT, 20-24 dpf). At 20 dpf, results revealed a significant effect of diet on the rate of caudal-peduncle scoliosis and gill-cover abnormalities, which were relatively elevated in B and C groups. SCT results focused on swimming-induced lordosis, which was comparatively elevated in diets C and D (83% ± 7% and 75% ± 10%, respectively, vs. 52% ± 18% in diet A). No significant effects of dry diets were observed on the survival and growth rate of zebrafish. Results are discussed with respect to the deferential diet composition between the groups and the species requirements. A potential nutritional control of haemal lordosis in finfish aquaculture is suggested.

Recent advances in the crosstalk between adipose, muscle and bone tissues in fish

Control of tissue metabolism and growth involves interactions between organs, tissues, and cell types, mediated by cytokines or direct communication through cellular exchanges. Indeed, over the past decades, many peptides produced by adipose tissue, skeletal muscle and bone named adipokines, myokines and osteokines respectively, have been identified in mammals playing key roles in organ/tissue development and function. Some of them are released into the circulation acting as classical hormones, but they can also act locally showing autocrine/paracrine effects. In recent years, some of these cytokines have been identified in fish models of biomedical or agronomic interest. In this review, we will present their state of the art focusing on local actions and inter-tissue effects. Adipokines reported in fish adipocytes include adiponectin and leptin among others. We will focus on their structure characteristics, gene expression, receptors, and effects, in the adipose tissue itself, mainly regulating cell differentiation and metabolism, but in muscle and bone as target tissues too. Moreover, lipid metabolites, named lipokines, can also act as signaling molecules regulating metabolic homeostasis. Regarding myokines, the best documented in fish are myostatin and the insulin-like growth factors. This review summarizes their characteristics at a molecular level, and describes both, autocrine effects and interactions with adipose tissue and bone. Nonetheless, our understanding of the functions and mechanisms of action of many of these cytokines is still largely incomplete in fish, especially concerning osteokines (i.e., osteocalcin), whose potential cross talking roles remain to be elucidated. Furthermore, by using selective breeding or genetic tools, the formation of a specific tissue can be altered, highlighting the consequences on other tissues, and allowing the identification of communication signals. The specific effects of identified cytokines validated through in vitro models or in vivo trials will be described. Moreover, future scientific fronts (i.e., exosomes) and tools (i.e., co-cultures, organoids) for a better understanding of inter-organ crosstalk in fish will also be presented. As a final consideration, further identification of molecules involved in inter-tissue communication will open new avenues of knowledge in the control of fish homeostasis, as well as possible strategies to be applied in aquaculture or biomedicine.

Effects of Dietary Phosphorus Levels on Growth Performance, Phosphorus Utilization and Intestinal Calcium and Phosphorus Transport-Related Genes Expression of Juvenile Chinese Soft-Shelled Turtle (Pelodiscus sinensis)

A 60-day feeding trial was performed to assess the effects of dietary phosphorus levels on growth performance, body composition, phosphorus utilization, plasma physiological parameters and intestinal Ca and P transport-related gene expression of juvenile Chinese soft-shelled turtle (P. sinensis). Four diets containing available P at graded levels of 0.88%, 1.00%, 1.18% and 1.63% (termed as D0.88, D1.00, D1.18 and D1.63, respectively) were formulated and each diet was fed to turtles (5.39 ± 0.02 g) in sextuplicate. The turtles were randomly distributed to 24 tanks with 8 turtles per tank. The results indicated that final body weight, specific growth rate, feed conversion ratio and protein efficiency ratio performed best in turtles fed 1.00% available P diet. The crude lipids of the whole body exhibited a decreasing trend with the dietary available P, whereas the calcium and phosphorus of the whole body and bone phosphorus showed an opposite tendency. The apparent digestibility coefficient of phosphorus declined with the dietary available P. Turtles fed 1.00% available phosphorus had the highest phosphorus retention ratio compared with other treatments. Simultaneously they had significantly lower phosphorus loss than turtles fed D1.18 and D1.63 and had no differences in this respect from turtles fed a low-phosphorus diet. It was noteworthy that the lowest plasma calcium concentrations, and alkaline phosphatase activities in plasma and liver, were discovered in turtles fed the diet containing 1.63% available phosphorus. In addition, the high-phosphorus diet resulted in significantly down-regulated expression of intestinal phosphorus and calcium transport-related key genes. In conclusion, the available phosphorus requirement of juvenile P. sinensis was determined at 1.041% (total phosphorus was 1.80%) based on quadratic regression of weight gain rate, and excessive dietary phosphorus stunted turtle growth possibly via inhibiting intestinal calcium absorption.

Hybridization alters the shape of the genotypic fitness landscape, increasing access to novel fitness peaks during adaptive radiation

Estimating the complex relationship between fitness and genotype or phenotype (i.e. the adaptive landscape) is one of the central goals of evolutionary biology. However, adaptive walks connecting genotypes to organismal fitness, speciation, and novel ecological niches are still poorly understood and processes for surmounting fitness valleys remain controversial. One outstanding system for addressing these connections is a recent adaptive radiation of ecologically and morphologically novel pupfishes (a generalist, molluscivore, and scale-eater) endemic to San Salvador Island, Bahamas. We leveraged whole-genome sequencing of 139 hybrids from two independent field fitness experiments to identify the genomic basis of fitness, estimate genotypic fitness networks, and measure the accessibility of adaptive walks on the fitness landscape. We identified 132 single nucleotide polymorphisms (SNPs) that were significantly associated with fitness in field enclosures. Six out of the 13 regions most strongly associated with fitness contained differentially expressed genes and fixed SNPs between trophic specialists; one gene (mettl21e) was also misexpressed in lab-reared hybrids, suggesting a potential intrinsic genetic incompatibility. We then constructed genotypic fitness networks from adaptive alleles and show that scale-eating specialists are the most isolated of the three species on these networks. Intriguingly, introgressed and de novo variants reduced fitness landscape ruggedness as compared to standing variation, increasing the accessibility of genotypic fitness paths from generalist to specialists. Our results suggest that adaptive introgression and de novo mutations alter the shape of the fitness landscape, providing key connections in adaptive walks circumventing fitness valleys and triggering the evolution of novelty during adaptive radiation.

Skeletal Biology and Disease Modeling in Zebrafish

Zebrafish are teleosts (bony fish) that share with mammals a common ancestor belonging to the phylum Osteichthyes, from which their endoskeletal systems have been inherited. Indeed, teleosts and mammals have numerous genetically conserved features in terms of skeletal elements, ossification mechanisms, and bone matrix components in common. Yet differences related to bone morphology and function need to be considered when investigating zebrafish in skeletal research. In this review, we focus on zebrafish skeletal architecture with emphasis on the morphology of the vertebral column and associated anatomical structures. We provide an overview of the different ossification types and osseous cells in zebrafish and describe bone matrix composition at the microscopic tissue level with a focus on assessing mineralization. Processes of bone formation also strongly depend on loading in zebrafish, as we elaborate here. Furthermore, we illustrate the high regenerative capacity of zebrafish bones and present some of the technological advantages of using zebrafish as a model. We highlight zebrafish axial and fin skeleton patterning mechanisms, metabolic bone disease such as after immunosuppressive glucocorticoid treatment, as well as osteogenesis imperfecta (OI) and osteopetrosis research in zebrafish. We conclude with a view of why larval zebrafish xenografts are a powerful tool to study bone metastasis. © 2021 American Society for Bone and Mineral Research (ASBMR).

The Role of Feed in Aquatic Laboratory Animal Nutrition and the Potential Impact on Animal Models and Study Reproducibility

Feed plays a central role in the physiological development of terrestrial and aquatic animals. Historically, the feeding practice of aquatic research species derived from aquaculture, farmed, or ornamental trades. These diets are highly variable, with limited quality control, and have been typically selected to provide the fastest growth or highest fecundity. These variations of quality and composition of diets may affect animal/colony health and can introduce confounding experimental variables into animal-based studies that impact research reproducibility.

More Bone with Less Minerals? The Effects of Dietary Phosphorus on the Post-Cranial Skeleton in Zebrafish

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, histology, TEM, synchrotron X-ray tomographic microscopy, nanoindentation) to describe in detail the effects of dietary P on the zebrafish skeleton, after two months of administering three different diets: 0.5% (low P, LP), 1.0% (regular P, RP), and 1.5% (high P, HP) total P content. LP zebrafish display growth retardation and hypomineralised bones, albeit without deformities. LP zebrafish increase production of non-mineralised bone matrix, and osteoblasts have enlarged endoplasmic reticulum cisternae, indicative for increased collagen synthesis. The HP diet promotes growth, high mineralisation, and stiffness but causes vertebral centra fusions. Structure and arrangement of bone matrix collagen fibres are not influenced by dietary P in all three groups. In conclusion, low dietary P content stimulates the formation of non-mineralised bone without inducing malformations. This indicates that bone formation and mineralisation are uncoupled. In contrast, high dietary P content promotes mineralisation and vertebral body fusions. This new zebrafish model is a useful tool to understand the mechanisms underlying osteomalacia and abnormal mineralisation, due to underlying variations in dietary P levels.

Effects of low dietary phosphorus on tibia quality and metabolism in caged laying hens

Osteoporosis is a common bone metabolic disease in caged laying hens. This disease affects animal welfare and economic costs. In this study, a model of osteoporosis induced by low dietary phosphorus was established. A total of sixty 22-week-old Roman white laying hens were randomly divided into two groups, including a control group (group C) and a low dietary phosphorus group (group P). The effects of low dietary phosphorus on the endocrine and tibial osteoprotegerin (OPG)/nuclear factor kappa B receptor activating factor ligand (RANKL) signaling pathways of osteoporosis in caged laying hens were analyzed by serology, bone biomechanics, molecular biology and histopathology. The results showed that low dietary phosphorus decreased the production performance, and egg quality of laying hens and increased the contents of serum calcium (Ca), osteocalcin (OCN), alkaline phosphatase (ALP) and tartrate-resistant acid phosphatase (TRACP). The contents of serum phosphorus, calcitonin (CT), OPG and tibial biomechanics index decreased. The bone mineral density (BMD), cortical bone thickness and the expression level of OPG protein in tibia decreased. The expression of OCN, nuclear factor kappa B receptor activating factor (RANK) and RANKL protein increased. Low dietary phosphorus caused thinning and fracture of the bone trabeculae and enlargement of the bone marrow cavity of tibia. Our results suggest that phosphorus may affect bone metabolism by regulating the OPG/RANKL signaling pathway.

Type II Na+-phosphate Cotransporters and Phosphate Balance in Teleost Fish

Teleost fish are excellent models to study the phylogeny of the slc34 gene family, Slc34-mediated phosphate (P_i) transport and how Slc34 transporters contribute P_i homeostasis. Fish need to accumulate P_i from the diet to sustain growth. Much alike in mammals, intestinal uptake in fish is partly a paracellular and partly a Slc34-mediated transcellular process. Acute regulation of P_i balance is achieved in the kidney via a combination of Slc34-mediated secretion and/or reabsorption. A great plasticity is observed in how various species perform and combine the different processes of secretion and reabsorption. A reason for this diversity is found in one or two whole genome duplication events followed by potential gene loss; consequently, teleosts exhibit distinctly different repertoires of Slc34 transporters. Moreover, due to habitats with vastly different salinity, teleosts face the challenge of either preserving water in a hyperosmotic environment (seawater) or excreting water in hypoosmotic freshwater. An additional challenge in understanding teleost P_i homeostasis are the genome duplication and retention events that diversified peptide hormones such as parathyroid hormone and stanniocalcin. Dietary P_i and non-coding RNAs also regulate the expression of piscine Slc34 transporters. The adaptive responses of teleost Slc34 transporters to e.g. P_i diets and vitamin D are informative in the context of comparative physiology, but also relevant in applied physiology and aquaculture. In fact, P_i is essential for teleost fish growth but it also exerts significant adverse consequences if over-supplied. Thus, investigating Slc34 transporters helps tuning the physiology of commercially valuable teleost fish in a confined environment.