Matrilin-1 expression is increased in the vertebral column of Atlantic salmon (Salmo salar L.) individuals displaying spinal fusions

Genomics and transcriptomics identify quantitative trait loci affecting growth-related traits in silver pomfret (Pampus argenteus)

Pampus argenteus, a species distributed throughout the Indo-West Pacific, plays a significant role in the yield of aquaculture species. However, cultured P. argenteus has always been characterised by unbalanced growth synchronisation among individuals, slow growth rate, and lack of excellent germplasm resources. Therefore, we conducted mass selection for fast-growing strain P. argenteus for several consecutive years. Various genetic improvement programs have modified its genome sequence through selective pressure, leaving nucleotide signals that can be detected at the genomic level. In the present study, we combined bulked segregant analysis and transcriptome sequencing to identify candidate single nucleotide polymorphisms (SNPs) and key genes for growth-related traits in P. argenteus. A total of 7,280,936 SNPs and 2,212,379 insertions/deletions were identified in the extreme phenotypes of the fast-growing and slow-growing groups. Based on the examination of SNP frequency differences and sliding-window analysis, 42 SNPs were identified as candidate markers. Moreover, 14 of the 42 SNPs linked to growth-related traits were confirmed to be credible SNPs, and eight growth-related genes were screened, namely myb-binding protein 1 A, insulin A/B chains, α-1B adrenoceptor, engulfment and cell motility protein 3, myosin light chain kinase family member 4, insulin receptor located, unconventional myosin-9b, and matrilin-1. An optimal three-factor model (SNP4&SNP12&SNP14) was constructed using the generalized multifactor dimensionality reduction method, and its accuracy was verified as 67.72 %. These results may benefit genetic studies and accelerate genetic improvement of fast-growing strains of P. argenteus.

Development of the Synarcual in the Elephant Sharks (Holocephali; Chondrichthyes): Implications for Vertebral Formation and Fusion

The synarcual is a structure incorporating multiple elements of two or more anterior vertebrae of the axial skeleton, forming immediately posterior to the cranium. It has been convergently acquired in the fossil group ‘Placodermi’, in Chondrichthyes (Holocephali, Batoidea), within the teleost group Syngnathiformes, and to varying degrees in a range of mammalian taxa. In addition, cervical vertebral fusion presents as an abnormal pathology in a variety of human disorders. Vertebrae develop from axially arranged somites, so that fusion could result from a failure of somite segmentation early in development, or from later heterotopic development of intervertebral bone or cartilage. Examination of early developmental stages indicates that in the Batoidea and the ‘Placodermi’, individual vertebrae developed normally and only later become incorporated into the synarcual, implying regular somite segmentation and vertebral development. Here we show that in the holocephalan Callorhinchus milii, uniform and regular vertebral segmentation also occurs, with anterior individual vertebra developing separately with subsequent fusion into a synarcual. Vertebral elements forming directly behind the synarcual continue to be incorporated into the synarcual through growth. This appears to be a common pattern through the Vertebrata. Research into human disorders, presenting as cervical fusion at birth, focuses on gene misexpression studies in humans and other mammals such as the mouse. However, in chondrichthyans, vertebral fusion represents the normal morphology, moreover, taxa such Leucoraja (Batoidea) and Callorhinchus (Holocephali) are increasingly used as laboratory animals, and the Callorhinchus genome has been sequenced and is available for study. Our observations on synarcual development in three major groups of early jawed vertebrates indicate that fusion involves heterotopic cartilage and perichondral bone/mineralised cartilage developing outside the regular skeleton. We suggest that chondrichthyans have potential as ideal extant models for identifying the genes involved in these processes, for application to human skeletal heterotopic disorders.

Small leucine-rich proteoglycans in the vertebrae of Atlantic salmon Salmo salar

We analysed the distribution and expression of the small leucine-rich proteoglycans (SLRPs) decorin, biglycan and lumican in vertebral columns of Atlantic salmon Salmo salar L. with and without radiographically detectable deformities. Vertebral deformities are a reoccurring problem in salmon and other intensively farmed species, and an understanding of the components involved in the pathologic development of the vertebrae is important in order to find adequate solutions to this problem. Using immunohistology and light microscopy, we found that in non-deformed vertebrae biglycan, lumican and decorin were all expressed in osteoblasts at the vertebral growth zones and at the ossification front of the chondrocytic arches. Hence, the SLRPs are expressed in regions where intramembranous and endochondral ossification take place. In addition, mRNA expression of biglycan, decorin and lumican was demonstrated in a primary osteoblast culture established from Atlantic salmon, supporting the in vivo findings. Transcription of the SLRPs increased during differentiation of the osteoblasts in vitro and where lumican mRNA expression increased later in the differentiation compared with decorin and biglycan. Intriguingly, in vertebral fusions, biglycan, decorin and lumican protein expression was extended to trans-differentiating cells at the border between arch centra and osteoblast growth zones. In addition, mRNA expression of biglycan, decorin and lumican differed between non-deformed and fused vertebrae, as shown by quantitative PCR (qPCR). Western blotting revealed an additional band of biglycan in fused vertebrae which had a higher molecular weight than in non-deformed vertebrae. Fourier-transform infrared (FTIR) spectroscopy revealed more spectral focality in the endplates of vertebral fusions and significantly more non-reducible collagen crosslinks compared with non-deformed vertebrae, thus identifying differences in bone structure.