Elucidating the early signaling cues involved in zebrafish chondrogenesis and cartilage morphology

Abnormal eyes and spine development in zebrafish (Danio rerio) embryos and larvae induced by triphenyltin

Triphenyltin (TPT) is widely used in crop pest control and ship antifouling coatings, which leads to its entry into aquatic environment and poses a threat to aquatic organisms. However, the effects of TPT on the early life stages of wild fish in natural water environments remains unclear. The aim of this study was to assess the toxic effects of TPT on the early life stages of fish under two different environments: field investigation and laboratory experiment. The occurrence of deformities in wild fish embryos and larvae in the Three Gorges Reservoir (TGR) and the developmental toxicity of TPT at different concentrations (0, 0.15, 1.5 and 15 μg Sn/L) to zebrafish embryos and larvae were observed. The results showed that TPT content was higher in wild larvae, reaching 27.21 ng Sn/g w, and the malformation of wild fish larvae mainly occurred in the eyes and spine under natural water environment. Controlled experiment exposure of zebrafish larvae to TPT also resulted in eye and spinal deformities. Gene expression analysis showed that compared with the control group, the expression levels of genes related to eye development (sox2, otx2, stra6 and rx1) and spine development (sox9a and bmp2b) were significantly up-regulated in the 15 μg Sn/L exposure group, which may be the main cause of eye and spine deformity in the early development stage of fish. In addition, the molecular docking results further elucidate that the strong hydrophobic and electrostatic interactions between TPT and protein residues are the main mechanism of TPT induced abnormal gene expression. Based on these results, it can be inferred that TPT is one of the teratogenic factors of abnormal eye and spine development in the early life stage of fish in the TGR. These findings have important implications for understanding the toxicity of TPT on fish.

Novel PFOS alternative OBS inhibits body growth of developing zebrafish by triggering thyroid function disorder and osteoclast differentiation

The extensive use of the perfluorooctane sulfonate (PFOS) alternative sodium p-perfluorous nonenoxybenzene sulfonate (OBS) has resulted in its widespread detection in the environment and enrichment in wildlife and humans. However, little is known about its potential toxicity, particularly in terms of body development. In this study, zebrafish embryos were acutely exposed to PFOS and OBS for a comparative developmental toxicity assessment. Both PFOS and OBS led to lower body weight and shorter body length, and the damaging effects of PFOS were more severe than those of OBS at the same exposure concentration. Biochemical assays of THs and transcription profiles correlated to the HPT axis demonstrated that OBS-induced body development inhibition resulted mainly from interference in THs synthesis, transfer, coupling with receptors, and conversion from T4 to T3, which was similar to the case of PFOS, except that the disruptive effects of OBS on thyroid function were more intense. Further transcriptome analysis showed that PFOS and OBS also promoted osteoclast differentiation, aggravating the inhibitory effects on body growth, and that PFOS had more obvious inhibitory effects than OBS. This study systematically explored the inhibitory effects of PFOS and OBS exposure on body development and tightly linked the toxic effects to thyroid function disorder and osteoclast differentiation. Our findings highlight that the health risks associated with OBS, an emerging substitute for PFOS, should not be ignored.

17β-Trenbolone activates androgen receptor, upregulates transforming growth factor beta/bone morphogenetic protein and Wnt signaling pathways, and induces masculinization of caudal and anal fins in female guppies (Poecilia reticulata)

Sexually mature female guppies (Poecilia reticulata) were exposed to environmentally relevant concentrations (20, 200, and 2000 ng/L) of 17β-trenbolone for four weeks. As evidenced by the increased caudal fin index and anal fins developing into gonopodium-like structures, exposed females displayed masculinized secondary sexual characteristics. Differential gene expression and subsequent pathway analysis of mRNA sequencing data revealed that the transcription of transforming growth factor beta/bone morphogenetic protein signaling pathway and Wnt signaling pathway were upregulated following 17β-trenbolone exposure. Enzyme-linked immunosorbent assays showed that the bone morphogenetic protein 7 protein content was elevated after 17β-trenbolone exposure. Finally, real-time PCR revealed that 17β-trenbolone treatment significantly increased androgen receptor mRNA levels, and molecular docking showed potent interaction between 17β-trenbolone and guppy androgen receptor. Furthermore, 17β-trenbolone-induced masculinization of caudal and anal fins in female guppies, concomitant to the upregulated expression of differentially expressed genes involved in the above-mentioned two signaling pathways, was significantly inhibited by flutamide (androgen receptor antagonist). These findings demonstrated that 17β-trenbolone masculinized fins of female guppies by activating the androgen receptor. This study revealed that 17β-trenbolone could upregulate signaling pathways related to fin growth and differentiation, and eventually cause caudal and anal fin masculinization in female guppies.

Intravitreal injection of FGF and TGF-β inhibitors disrupts cranial cartilage development

Cartilage development is a tightly regulated process that requires the interaction of epithelial and mesenchymal tissues layers to initiate the aggregation of mesenchyme in a condensation. Several signaling molecules have been implicated in cartilage formation including FGFs, WNTs, and members of the TGF-β super family. However, little is known about the earliest signals involved in these initial phases of development. Here we aimed to investigate whether direct intravitreal injection of pharmaceutical inhibitors for FGF and TGF-β signaling would perturb cranial cartilages in zebrafish. Via wholemount bone and cartilage staining, we found effects on multiple cranial cartilage elements. We found no effect on scleral cartilage development, however, the epiphyseal bar, basihyal, and basicapsular cartilages were disrupted. Interestingly, the epiphyseal bar arises from the same progenitor pool as the scleral cartilage, namely, the periocular ectomesenchyme. This study adds to the foundational knowledge about condensation induction of cranial cartilage development and provides insight into the timing and signaling involved in the early development of several craniofacial cartilage elements in zebrafish.

Quantification and comparison of teleost scleral cartilage development and growth

The ocular skeleton is composed of the scleral cartilage and the scleral ossicles. Teleost scleral cartilage is composed of a single layer of chondrocytes embedded in the sclera of the eye. The teleost scleral cartilage ring can vary in depth across teleost families and species, from a narrow ring a few cells wide to a deeper ring that resembles a cup and surrounds the entire sclera. However, very little research has been conducted on the development and morphology of teleost scleral cartilage. Thus, this study aims to characterize the development of the scleral cartilage in the zebrafish and Mexican tetra, with respect to the timing of emergence, depth throughout development, and positioning within the eye. We hypothesized that the scleral cartilage would first emerge in the scleral tissue closely abutting the ora serrata, and that growth would proceed in an anterior-to-posterior direction, resulting in differences in scleral cartilage depth between different fish species. We found that the scleral cartilage ring does not develop uniformly along its circumference, and that its relationship to the ora serrata varies between the rostral and caudal regions. Furthermore, distinct differences in the growth trajectory of the scleral cartilage indicate that the deep scleral cartilage of the Pachón cavefish is the result of both decreased eye size and prolonged cartilage growth. A significant difference in the size of the scleral chondrocytes was also noted. Overall, this study provides the first characterization of early scleral cartilage development in teleost fish and indicates that some aspects of scleral cartilage development and morphology are highly conserved while others are not.

Vibration exposure uncovers a critical early developmental window for zebrafish caudal fin development

Mechanical influencers have long been shown to affect mature bone. Bone mechanosensation is a key feature that allows the skeleton to adapt to environmental constraints. In this study, we describe the response of immature, developing bones to a mechanical stimulus. To do so, zebrafish larvae at different stages of development were exposed to whole-body vibration (WBV) at a low frequency of 20 Hz, for up to 4 days. Whole mount Alizarin red and Alcian blue staining revealed age-related and bone type-specific defects. Specifically, the parhypural and hypural 1 caudal fin endoskeletal elements were affected when the exposure to WBV started early during their development. We show that these WBV-induced parhypural and hypural 1 patterning defects are triggered by a Sox9-independent pathway, potentially by reducing the distance separating adjacent chondrogenic condensations in the developing tail skeleton. The remaining hypurals were unaffected by the WBV treatment. Altogether, our results indicate that, upon exposure to vibration, chondrogenic cell progenitors can react to mechanical stimuli early during their development, which ultimately affects the skeletal patterning of the growing zebrafish larvae. These findings open a new research avenue to better understand the cellular processes involved in developing, patterning, and maintaining skeletal tissue.

Probiotics Enhance Bone Growth and Rescue BMP Inhibition: New Transgenic Zebrafish Lines to Study Bone Health

Zebrafish larvae, especially gene-specific mutants and transgenic lines, are increasingly used to study vertebrate skeletal development and human pathologies such as osteoporosis, osteopetrosis and osteoarthritis. Probiotics have been recognized in recent years as a prophylactic treatment for various bone health issues in humans. Here, we present two new zebrafish transgenic lines containing the coding sequences for fluorescent proteins inserted into the endogenous genes for sp7 and col10a1a with larvae displaying fluorescence in developing osteoblasts and the bone extracellular matrix (mineralized or non-mineralized), respectively. Furthermore, we use these transgenic lines to show that exposure to two different probiotics, Bacillus subtilis and Lactococcus lactis, leads to an increase in osteoblast formation and bone matrix growth and mineralization. Gene expression analysis revealed the effect of the probiotics, particularly Bacillus subtilis, in modulating several skeletal development genes, such as runx2, sp7, spp1 and col10a1a, further supporting their ability to improve bone health. Bacillus subtilis was the more potent probiotic able to significantly reverse the inhibition of bone matrix formation when larvae were exposed to a BMP inhibitor (LDN212854).