Continuous light affects mineralization and delays osteoid incorporation in vertebral bone of Atlantic salmon (Salmo salar L.)

Abstract

SUMMARYIn order to study the effects of photoperiod on fish bone, Atlantic salmon (Salmo salar L.) were exposed to two light regimes (natural and continuous light) from January until June. During the experimental period, several parameters related to the inorganic (minerals) and organic (osteoid) phases were measured. Changes in the organic phase were related to mechanical strength (yield-load) and the expression of the genes sonic hedgehog (shh) and collagen type I alpha 2 (col I). Co-variation between yield-load and the expression of both shh and col I were detected in both groups. It was also shown that fish on the continuous light regime had delayed activation of osteoid incorporation. Mineralization properties were measured with stiffness, mineral incorporation per day and expression of alkaline phosphatase (alp) and matrix Gla protein (mgp). Stiffness, mineral incorporation and gene expression followed the same trend in both light groups in late spring, whereas an increase in the expression of mgp and alp was detected in April, followed by significantly higher stiffness at last sampling in both light groups. These results indicate that constant light affects mineralization and delays osteoid incorporation in Atlantic salmon during the spring. However, in this experiment light treatment did not promote the development of vertebral deformities. Our results also suggest that shh can be used as a marker of osteoblast proliferation and col I a marker of osteoid incorporation, and that both alp and mgp expression could be associated with a rapid increase in mineralization in Atlantic salmon vertebrae.

Collagen type XI α1 may be involved in the structural plasticity of the vertebral column in Atlantic salmon (Salmo salar L.)

“…Considering the complex effect that continuous light has on the vertebrae (Fjelldal et al, 2005;Nordgarden et al, 2006;Wargelius et al, 2009), the induction of eight genes must be regarded as a low number, a number that was even lower in experiment 2. However, much of the effect may have been masked by the circadian rhythm of bone tissue, and as is known in mouse bone, 26% of the transcriptome exhibits a circadian pattern (Zvonic et al, 2007).…”

Transcriptome sequencing of Atlantic salmon (Salmo salar L.) notochord prior to development of the vertebrae provides clues to regulation of positional fate, chordoblast lineage and mineralisation

“…Primers were designed using Primer Express v2.0 software (Applied Biosystems Inc.) and Primer-BLAST [24]. Elongation factor 1 α ( ef1a ) was used as reference gene for its stable expression in salmon tissues [25], including notochord [10,13,26]. ef1a was expressed at the same level in all libraries (Gene expression data found at https://marineseq.imr.no/salmon/annot2013/).…”

Vertebral deformities in farmed Atlantic salmon (Salmo salar L.) - etiology and pathology

“…Furthermore, the vitamin D system is affected by the photoperiod (Fjelldal et al., 2012a). Removal of the light sensitive pineal gland (Fjelldal et al., 2004), photoperiod manipulation (Fjelldal et al., 2005; Wargelius et al., 2009), and water temperature (growth rate) elevation (Grini et al., 2011) all affects vertebral bone mineralization in Atlantic salmon. A recent study where Atlantic salmon underyearling postsmolts were fed a high or low phosphorus diet under continuous light or LD 12:12 and at elevated temperature, showed that only the combination of continuous light and low dietary phosphorus induced vertebral body compressions with a concomitant increase in plasma calcitriol (Fjelldal et al., 2012a).…”