Developmental effects related to angiogenesis and osteogenic differentiation in Atlantic salmon (Salmosalar) larvae exposed to dioxin-like polychlorinated biphenyl congener 77 (PCB-77)
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- Institutt for biologi 
This study was conducted to investigate the relationship between 3,3’,4,4’-tetra-chlorobiphenyl(PCB-77) induced aryl hydrocarbon receptor (AhR) signalling and down-streamimpacts on detoxification, angiogenesis and ossification during early lifestages in Atlanticsalmon (Salmo salar). Both genotypic and phenotypic alterations were investigated. This wasexecuted by evaluating development of bone in larvae, both by observing skeletal structureformation and by investigating gene expression levels of genes related to ossification process.We also wanted to investigate possible competition for aryl hydrocarbon receptor nucleartranslocator (ARNT) between ligand activated AhR and hypoxia inducible factor 1 alpha(HIF-1a), and down-stream target vascular endothelial growth factor (VEGF) which initiatesangiogenesis. Gene expression levels of VEGF were related to observation of heart rate,arrhythmia and anaemia, giving a comprehensive picture of vascular system development.Larvae were continuously exposed to waterborne PCB-77 (1 or 10 ng/L) initiated at egg stage(416 day degrees (dd)) and throughout yolk sac stage (716 dd), for a duration of 50 days (300dd). Gene transcription analysis was performed on whole larvae total RNA from 548, 632,674 and 716 dd using quantitative (real-time) polymerase chain reaction (qRT-PCR) withgene specific primers for AhR2 isoforms (a, b, d and g), ARNT, aryl hydrocarbon receptorrepressor (AhRR), cytochrome P450 1A1 (CYP1A1), HIF-1a, VEGF, bone morphogenetic proteins (BMPs) (2 and 4), runx2, sox9 and collagen type 2 alpha 1 (col2a1). Based on initialobservations, phenotypic response was analysed at ages 506, 632 and 716 dd.Ossification of pectoral-, tail-, dorsal-, pelvic- and anal fin rays, haemal and neural arches wasinvestigated. Estrogen receptor (ER) pathway regulates osteoblast activity and PCB-77 isknown to increase ER activity through AhR signalling pathway. Bone staining (Alizarin red)shows an increased rate in osteogenic tissue production correlated with increased exposureconcentration (PCB-77). Gene expression analysis revealed increase of col2a1 and runx2,inducing chondrogenesis and osteogenesis, respectively. Indications of vascular system disruption of development caused by PCB-77, were observedas anaemia and arrhythmia in exposed individuals and a decreased level of VEGF expression,compared to control. Data did not suggest interaction between AhR and HIF-1a for theircommon heterodimerc partner ARNT, indicating that PCB-77 may disrupt development ofvascular system through other signalling pathways.