The biological role of vitamin D receptors (VDR), which are abundantly expressed in developing zebrafish (Danio rerio) as early as 48 h after fertilization, and before the development of a mineralized skeleton and mature intestine and kidney,
is unknown. We probed the role of VDR in developing zebrafish biology by examining changes in expression of RNA by whole transcriptome
shotgun sequencing (RNA-seq) in fish treated with picomolar concentrations of the VDR ligand and hormonal form of vitamin
D3, 1α,25-dihydroxyvitamin D3 [1α,25(OH)2D3)].We observed significant changes in RNAs of transcription factors, leptin, peptide hormones, and RNAs encoding proteins
of fatty acid, amino acid, xenobiotic metabolism, receptor-activator of NFκB ligand (RANKL), and calcitonin-like ligand receptor
pathways. Early highly restricted, and subsequent massive changes in more than 10% of expressed cellular RNA were observed.
At days post fertilization (dpf) 2 [24 h 1α,25(OH)2D3-treatment], only four RNAs were differentially expressed (hormone vs. vehicle). On dpf 4 (72 h treatment), 77 RNAs; on dpf 6 (120 h treatment) 1039 RNAs; and on dpf 7 (144 h treatment), 2407
RNAs were differentially expressed in response to 1α,25(OH)2D3. Fewer RNAs (n = 481) were altered in dpf 7 larvae treated for 24 h with 1α,25(OH)2D3vs. those treated with hormone for 144 h. At dpf 7, in 1α,25(OH)2D3-treated larvae, pharyngeal cartilage was larger and mineralization was greater. Changes in expression of RNAs for transcription
factors, peptide hormones, and RNAs encoding proteins integral to fatty acid, amino acid, leptin, calcitonin-like ligand receptor,
RANKL, and xenobiotic metabolism pathways, demonstrate heretofore unrecognized mechanisms by which 1α,25(OH)2D3 functions in vivo in developing eukaryotes.