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First published online 5 September 2007
doi: 10.1242/dev.004572

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Drosophila Niemann-Pick Type C-2 genes control sterol homeostasis and steroid biosynthesis: a model of human neurodegenerative disease

¹ Departments of Developmental Biology, Genetics and Bioengineering, Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, CA 94305-5439, USA.
² Laboratory of Molecular and Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing, 100101, China.
³ Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3280, USA.
⁴ Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305-5439, USA.

^* Author for correspondence (e-mail: mscott{at}stanford.edu)

Accepted 18 July 2007

Mutations in either of the two human Niemann-Pick type C (NPC) genes, NPC1 and NPC2, cause a fatal neurodegenerative disease associated with abnormal cholesterol accumulation in cells. npc1a, the Drosophila NPC1 ortholog, regulates sterol homeostasis and is essential for molting hormone (20-hydroxyecdysone; 20E) biosynthesis. While only one npc2 gene is present in yeast, worm, mouse and human genomes, a family of eight npc2 genes (npc2a-h) exists in Drosophila. Among the encoded proteins, Npc2a has the broadest expression pattern and is most similar in sequence to vertebrate Npc2. Mutation of npc2a results in abnormal sterol distribution in many cells, as in Drosophila npc1a or mammalian NPC mutant cells. In contrast to the ecdysteroid-deficient, larval-lethal phenotype of npc1a mutants, npc2a mutants are viable and fertile with relatively normal ecdysteroid level. Mutants in npc2b, another npc2 gene, are also viable and fertile, with no significant sterol distribution abnormality. However, npc2a; npc2b double mutants are not viable but can be rescued by feeding the mutants with 20E or cholesterol, the basic precursor of 20E. We conclude that npc2a functions redundantly with npc2b in regulating sterol homeostasis and ecdysteroid biosynthesis, probably by controlling the availability of sterol substrate. Moreover, npc2a; npc2b double mutants undergo apoptotic neurodegeneration, thus constituting a new fly model of human neurodegenerative disease.

Key words: Niemann-Pick type C, Sterol, Ecdysteroid, Drosophila

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