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Vitamin D exerts various physiological functions such as osteogenesis, antitumor and immunomodulatory effects, all of which are intimately involved in health promotion. The canonical molecular pathway of vitamin D involves the binding of 1,25-dihydroxyvitamin D₃ (1α,25(OH) ₂D₃), an active form of vitamin D, to the vitamin D receptor (VDR). In addition to the existing mechanism of vitamin D, however, novel molecular mechanisms underlying the functions of vitamin D, including the VDR-independent action of 1α,25(OH) ₂D₃ and a direct action of 25-hydroxyvitamin D₃ (25(OH)D₃, a precursor of 1α,25(OH) ₂D₃), has been reported recently. Further elucidation of the mechanisms for these novel functions of vitamin D may bring a useful information for new drug discovery targets and health promotion strategies. In order to elucidate the molecular mechanisms for novel physiological functions of vitamin D in vivo, we generated several animal models of rickets in which vitamin D-related genes, such as Cyp27b1 and Vdr, have been inactivated by the genetic engineering method. This review aims to introduce our findings obtained from comparative phenotypic studies using these animal models of rickets and to show the usefulness of these animal models for vitamin D-related research.

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N -Acylethanolamines (NAEs) are a class of lipid mediators and widely present in various organisms including animals and plants. NAEs are ethanolamides of long-chain fatty acids and exhibit a variety of biological activities such as anti-inflammation, analgesia, and appetite suppression. NAEs are produced from membrane glycerophospholipids and act as the trigger of signal transduction and gene expression through receptors. Studies over the past three decades have identified a series of enzymes involved in the generation and degradation of NAEs and clarified the complexity of their metabolic pathways. N -Acyltransferase initiates the biosynthesis of NAEs and is regarded as the rate-limiting enzyme regulating the levels of NAEs. The enzyme produces the precursor of NAEs, N -acylphosphatidylethanolamine, by transferring an acyl chain of glycerophospholipids to the amino group of phosphatidylethanolamine. Two types of N -acyltransferases have been identified: Ca²⁺-dependent cytosolic phospholipase A₂ε (cPLA₂ε) and Ca²⁺-independent phospholipase A and acyltransferase (PLAAT) family members. These N -acyltransferases differ in primary structures, enzymatic properties, and tissue distributions, and thus have been thought to function in distinct occasions. In this minireview, we overview recent advances in the field of NAE research, focusing on the physiological and pathophysiological functions of cPLA₂ε and PLAAT family revealed by the analysis of knockout mice of these enzymes.

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