Two syntaxin homologues in the TGN/endosomal system of yeast.

Intracellular membrane traffic is thought to be regulated in part by SNAREs, integral membrane proteins on transport vesicles (v-SNAREs) and target organelles (t-SNAREs) that bind to each other and mediate bilayer fusion. All known SNARE-mediated fusion events involve a member of the syntaxin family of t-SNAREs. Sequence comparisons identify eight such proteins encoded in the yeast genome, of which six have been characterized. We describe here the remaining two, Tlg1p and Tlg2p. These have the expected biochemical properties of t-SNAREs, and are located in separable compartments which correspond to a putative early endosome and the yeast equivalent of the TGN, respectively. They co-precipitate with the v-SNARE Vti1p, which is implicated in Golgi-endosome traffic and, remarkably, binds to five different syntaxins. Tlg1p also binds the plasma membrane v-SNARE Snc1p. Both Tlg1p and Tlg2p are required for efficient endocytosis and to maintain normal levels of TGN proteins. However, neither is required for intra-Golgi traffic. Since no further syntaxins have been identified in yeast, this implies that the Golgi apparatus can function with a single syntaxin, Sed5p

A genetic basis for functional hypothalamic amenorrhea.

Background: Functional hypothalamic amenorrhea is a reversible form of gonadotropin-releasing hormone (GnRH) deficiency commonly triggered by stressors such as excessive exercise, nutritional deficits, or psychological distress. Women vary in their susceptibility to inhibition of the reproductive axis by such stressors, but it is unknown whether this variability reflects a genetic predisposition to hypothalamic amenorrhea. We hypothesized that mutations in genes involved in idiopathic hypogonadotropic hypogonadism, a congenital form of GnRH deficiency, are associated with hypothalamic amenorrhea. Methods: We analyzed the coding sequence of genes associated with idiopathic hypogonadotropic hypogonadism in 55 women with hypothalamic amenorrhea and performed in vitro studies of the identified mutations. Results: Six heterozygous mutations were identified in 7 of the 55 patients with hypothalamic amenorrhea: two variants in the fibroblast growth factor receptor 1 gene FGFR1 (G260E and R756H), two in the prokineticin receptor 2 gene PROKR2 (R85H and L173R), one in the GnRH receptor gene GNRHR (R262Q), and one in the Kallmann syndrome 1 sequence gene KAL1 (V371I). No mutations were found in a cohort of 422 controls with normal menstrual cycles. In vitro studies showed that FGFR1 G260E, FGFR1 R756H, and PROKR2 R85H are loss-of-function mutations, as has been previously shown for PROKR2 L173R and GNRHR R262Q. Conclusions: Rare variants in genes associated with idiopathic hypogonadotropic hypogonadism are found in women with hypothalamic amenorrhea, suggesting that these mutations may contribute to the variable susceptibility of women to the functional changes in GnRH secretion that characterize hypothalamic amenorrhea. Our observations provide evidence for the role of rare variants in common multifactorial disease. (Funded by the Eunice Kennedy Shriver National Institute of Child Health and Human Development and others; ClinicalTrials.gov number, NCT00494169.