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Whereas the physiological significance of microsomal fatty acid elongation is generally appreciated, its molecular nature is poorly understood. Here, we describe tissue-specific regulation of a novel mouse gene family encoding components implicated in the synthesis of very long chain fatty acids. The Ssc1 gene appears to be ubiquitously expressed, whereas Ssc2 and Cig30 show a restricted expression pattern. Their translation products are all integral membrane proteins with five putative transmembrane domains. By complementing the homologous yeast mutants, we found that Ssc1 could rescue normal sphingolipid synthesis in the sur4/elo3 mutant lacking the ability to synthesize cerotic acid (C26:0). Similarly, Cig30 reverted the phenotype of the fen1/elo2 mutant that has reduced levels of fatty acids in the C20–C24 range. Further, we show that Ssc1 mRNA levels were markedly decreased in the brains of myelin-deficient mouse mutants known to have very low fatty acid chain elongation activity. Conversely, the dramatic induction of Cig30 expression during brown fat recruitment coincided with elevated elongation activity. Our results strongly implicate this new mammalian gene family in tissue-specific synthesis of very long chain fatty acids and sphingolipids.

Very little is known about the in vivo regulation of mammalian fatty acid chain elongation enzymes as well as the role of specific fatty acid chain length in cellular responses and developmental processes. Here, we report that the Elovl3 gene product, which belongs to a highly conserved family of microsomal enzymes involved in the formation of very long chain fatty acids, revealed a distinct expression in the skin that was restricted to the sebaceous glands and the epithelial cells of the hair follicles. By disruption of the Elovl3 gene by homologous recombination in mouse, we show that ELOVL3 participates in the formation of specific neutral lipids that are necessary for the function of the skin. The Elovl3-ablated mice displayed a sparse hair coat, the pilosebaceous system was hyperplastic, and the hair lipid content was disturbed with exceptionally high levels of eicosenoic acid (20:1). This was most prominent within the triglyceride fraction where fatty acids longer than 20 carbon atoms were almost undetectable. A functional consequence of this is that Elovl3-ablated mice exhibited a severe defect in water repulsion and increased trans-epidermal water loss.Fatty acids consisting of up to 16 carbons are synthesized by the well studied fatty acid synthase complex (1). However, a significant amount of the fatty acids produced by fatty acid synthase are further elongated into very long chain fatty acids (VLCFA). 1 VLCFA have been recognized as structural components in a variety of fat molecules such as glycerolipids and sphingolipids. They are found in virtually all cells and are major constituents of the brain, skin, and testis (2-4). Depending on their chain length and degree of unsaturation, they contribute to membrane fluidity and other chemical properties of the cell.Formation of VLCFA is performed in the endoplasmic reticulum, in the early Golgi, and in mitochondria by membranebound enzymes, the former being more prominent (5, 6).Recently, five mammalian genes, Elovl1-5, 2 whose protein products belong to a highly conserved family of microsomal enzymes involved in the formation of VLCFA, have been identified (7-10). All five genes show a diverse tissue-specific expression pattern indicating a unique role for different VLCFA in different cell types.Although the general functions of the Elovl genes are partially understood (8 -14), very little is known about the role of specific fatty acid chain length in cellular responses and developmental processes. The ELOVL3 protein has been suggested to be involved in the formation of saturated and monounsaturated fatty acyl chains containing up to 24 carbon atoms (9). Elovl3 gene expression has only been detected in brown adipose tissue, liver, and skin (7, 9). To assess the in vivo role of ELOVL3, we disrupted the Elovl3 gene by homologous recombination in mouse. Here we describe the characterization of Elovl3 expression in skin and present evidence that ELOVL3 participates in the formation of certain VLCFA and triglycerides in certain cells of the hair follicles and...

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In this paper, we present a novel method for joint estimation of the fundamental frequency and order of a set of harmonically related sinusoids based on the MUSIC estimation criterion. The presented method, termed HMUSIC, is shown to have an efficient implementation using FFTs. Furthermore, refined estimates can be obtained using a gradient-based method. Illustrative examples of the application of the algorithm to real-life speech and audio signals are given, and the statistical performance of the estimator is evaluated using synthetic signals, demonstrating its good statistical properties.

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In this paper, we consider the problem of separating and enhancing periodic signals from single-channel noisy mixtures. More specifically, the problem of designing filters for such tasks is treated. We propose a number of novel filter designs that 1) are specifically aimed at periodic signals, 2) are optimal given the observed signal and thus signal adaptive, 3) offer full parametrizations of periodic signals, and 4) reduce to well-known designs in special cases. The found filters can be used for a multitude of applications including processing of speech and audio signals. Some illustrative signal examples demonstrating its superior properties as compared to other related filters are given and the properties of the various designs are analyzed using synthetic signals in Monte Carlo simulations.