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

Abstract

Across the teleost skeleton, cartilages are diverse in their composition suggesting subtle differences in their developmental mechanisms. This study aims to elucidate the regulatory role of bone morphogenetic protein (BMPs) during the morphogenesis of two cartilage elements in zebrafish: the scleral cartilage in the eye and the caudal fin endoskeleton. Zebrafish larvae were exposed to a BMP inhibitor (LDN193189) at a series of timepoints preceding the initial appearance of the scleral cartilage and caudal fin endoskeleton. Morphological assessments of the cartilages in later stages, revealed that BMP‐inhibited fish harbored striking disruptions in caudal fin endoskeletal morphology, regardless of the age at which the inhibitor treatment was performed. In contrast, scleral cartilage morphology was unaffected in all age groups. Morphometric and principal component analysis, performed on the caudal fin endoskeleton, revealed differential clustering of principal components one and two in BMP‐inhibited and control fish. Additionally, the expression of sox9a and sox9b were reduced in BMP‐inhibited fish when compared to controls, indicating that LDN193189 acts via a Sox9‐dependent pathway. Further examination of notochord flexion also revealed a disruptive effect of BMP inhibition on this process. This study provides a detailed characterization of the effects of BMP inhibition via LDN193189 on zebrafish cartilage morphogenesis and development. It highlights the specific, localized role of the BMP‐signaling pathways during the development of different cartilage elements and sheds some light on the morphological characteristics of fossil teleosts that together suggest an uncoupling of the developmental processes between the upper and lower lobes of the caudal fin.

Quantification and comparison of teleost scleral cartilage development and growth

“…The teleost scleral cartilage is highly robust element, considering its conserved morphology, and its ability to resist perturbation (Zinck et al, 2021). Robust elements suggest a deep evolutionary history characterized by phenotypic stability in light of genetic and environmental variation (Félix & Wagner, 2008).…”

“…Specifically, we aim to determine the pattern of scleral cartilage development and growth in teleosts with different scleral cartilage morphology and provide an in-depth quantification of our findings. Based on previous examinations of teleost scleral cartilage in adult and juvenile fish (Franz-Odendaal et al, 2007;Zinck et al, 2021), we hypothesize that scleral cartilage induction would first occur in the sclera near the anterior-most extent of the optic cup tissues (i.e., near the ora serrata, the connection point between the retinal pigmented epithelium and the neural retina). Secondly, we hypothesize that in fish with deeper scleral cartilage rings (e.g., the Pachón cave tetra), that growth will continue in the posterior direction (toward the back of the eye) and that in species with narrow scleral cartilage rings, growth will be halted after chondrogenesis has occurred, resulting in a narrow ring of scleral cartilage.…”

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

“…BMP signalling is known to be required for osteoblast differentiation and for bone mineralization [37,38]. The most eminent marker gene widely used for investigating osteoblast differentiation in mammals and teleost species is the sp7 gene [39][40][41].…”