mice by homologous recombination Abstract ELOVL2 is a member of the mammalian mi- crosomal ELOVL fatty acid enzyme family, involved in the elongation of very long-chain fatty acids including PUFAs

Journal of Lipid Research Volume 52, 2011 245 Copyright © 2011 by the American Society for Biochemistry and Molecular Biology, Inc. Essential fatty acids, i.e., linoleic (C18:2n-6) and -linolenic acid (C18:3n-3), which are prerequisites for normal growth, development, and function in mammals, cannot be synthesized de novo and, as such, have to be derived from diet ( 1 ). Subsequently, the C18:2n-6 and C18:3n-3 fatty acids can be converted into other PUFAs through a series of elongation and desaturation steps performed by distinct enzymes residing in the endoplasmic reticulum ( 2 ). Desaturation steps are performed by the 5and 6desaturases, while chain elongation is controlled by the elongation of very-long-chain fatty acid (ELOVL) enzymes, ELOVL2, ELOVL4, and ELOVL5. ELOVL4 is believed to be involved in the elongation of PUFAs in the retina, brain, skin, and testis ( 3 ). Using cultured cells that overexpress this protein, it has been shown that ELOVL4 is involved in the synthesis of saturated C28 and C30 very-long-chain FA (VLCFA), as well as polyunsaturated C28–C38 VLCPUFAs such as the C34:6n-3 and C36:6n-3 fatty acids ( 4 ). ELOVL5 predominantly elongates C18 PUFAs up to 22 carbons in length, while ELOVL2 has been shown to be involved in the elongation of C20 and C22 PUFA in order to produce C24:4n-6 and C24:5n-3 PUFAs ( 5–7 ). These latter two are also recognized as precursors for docosapentaenoic acid (C22:5n-6) and docosahexaenoic acid (DHA) (C22:6n-3) synthesis, respectively, via the so-called Sprecher pathway, which includes one step of  oxidation/ chain shortening ( 8 ). To assess the in vivo function of ELOVL2, we generated Elovl2 +/ and Elovl2 / mice by homologous recombination Abstract ELOVL2 is a member of the mammalian microsomal ELOVL fatty acid enzyme family, involved in the elongation of very long-chain fatty acids including PUFAs required for various cellular functions in mammals. Here, we used ELOVL2-ablated ( Elovl2 / ) mice to show that the PUFAs with 24–30 carbon atoms of the -6 family in testis are indispensable for normal sperm formation and fertility in male mice. The lack of Elovl2 was associated with a complete arrest of spermatogenesis, with seminiferous tubules displaying only spermatogonia and primary spermatocytes without further germinal cells. Furthermore, based on acyl-CoA profi ling, heterozygous Elovl2 +/ male mice exhibited haploinsuffi ciency, with reduced levels of C28:5 and C30:5n-6 PUFAs, which gave rise to impaired formation and function of haploid spermatides. These new insights reveal a novel mechanism involving ELOVL2-derived PUFAs in mammals and previously unrecognized roles for C28 and C30 n-6 PUFAs in male fertility. In accordance with the function suggested for ELOVL2, the Elovl2 / mice show distorted levels of serum C20 and C22 PUFAs from both the n-3 and the n-6 series. However, dietary supplementation with C22:6n-3 could not restore male fertility to Elovl2 +/