title: Positional cloning of a type 2 diabetes quantitative trait locus; tomosyn-2, a negative regulator of insulin secretion.
abstract: We previously mapped a type 2 diabetes (T2D) locus on chromosome 16 (Chr 16) in an F2 intercross from the BTBR T (+) tf (BTBR) Lep(ob/ob) and C57BL/6 (B6) Lep(ob/ob) mouse strains. Introgression of BTBR Chr 16 into B6 mice resulted in a consomic mouse with reduced fasting plasma insulin and elevated glucose levels. We derived a panel of sub-congenic mice and narrowed the diabetes susceptibility locus to a 1.6 Mb region. Introgression of this 1.6 Mb fragment of the BTBR Chr 16 into lean B6 mice (B6.16(BT36-38)) replicated the phenotypes of the consomic mice. Pancreatic islets from the B6.16(BT36-38) mice were defective in the second phase of the insulin secretion, suggesting that the 1.6 Mb region encodes a regulator of insulin secretion. Within this region, syntaxin-binding protein 5-like (Stxbp5l) or tomosyn-2 was the only gene with an expression difference and a non-synonymous coding single nucleotide polymorphism (SNP) between the B6 and BTBR alleles. Overexpression of the b-tomosyn-2 isoform in the pancreatic β-cell line, INS1 (832/13), resulted in an inhibition of insulin secretion in response to 3 mM 8-bromo cAMP at 7 mM glucose. In vitro binding experiments showed that tomosyn-2 binds recombinant syntaxin-1A and syntaxin-4, key proteins that are involved in insulin secretion via formation of the SNARE complex. The B6 form of tomosyn-2 is more susceptible to proteasomal degradation than the BTBR form, establishing a functional role for the coding SNP in tomosyn-2. We conclude that tomosyn-2 is the major gene responsible for the T2D Chr 16 quantitative trait locus (QTL) we mapped in our mouse cross. Our findings suggest that tomosyn-2 is a key negative regulator of insulin secretion.
authors: Department of Biochemistry, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.
authors: Sushant
authors: S
authors: Bhatnagar
authors: Angie T
authors: AT
authors: Oler
authors: Mary E
authors: ME
authors: Rabaglia
authors: Donald S
authors: DS
authors: Stapleton
authors: Kathryn L
authors: KL
authors: Schueler
authors: Nathan A
authors: NA
authors: Truchan
authors: Sara L
authors: SL
authors: Worzella
authors: Jonathan P
authors: JP
authors: Stoehr
authors: Susanne M
authors: SM
authors: Clee
authors: Brian S
authors: BS
authors: Yandell
authors: Mark P
authors: MP
authors: Keller
authors: Debbie C
authors: DC
authors: Thurmond
authors: Alan D
authors: AD
authors: Attie
mesh_terms: D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D033942:Adaptor Proteins, Vesicular Transport; D000818:Animals; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D003924:Diabetes Mellitus, Type 2 / Q000235:genetics*; D004195:Disease Models, Animal; D020022:Genetic Predisposition to Disease; D005947:Glucose / Q000032:analysis; D057809:HEK293 Cells; D006801:Humans; D007003:Hypoglycemia / Q000235:genetics; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000378:metabolism / Q000473:pathology; D020738:Leptin / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D020641:Polymorphism, Single Nucleotide; D050765:Qa-SNARE Proteins / Q000235:genetics / Q000378:metabolism; D040641:Quantitative Trait Loci / Q000235:genetics; D050683:R-SNARE Proteins / Q000235:genetics* / Q000378:metabolism*; D051381:Rats; D050600:SNARE Proteins / Q000378:metabolism; D050827:Syntaxin 1 / Q000235:genetics / Q000378:metabolism
chemical_list: D033942:Adaptor Proteins, Vesicular Transport; D007328:Insulin; D020738:Leptin; D050765:Qa-SNARE Proteins; D050683:R-SNARE Proteins; D050600:SNARE Proteins; C492530:STXBP5L protein, mouse; D050827:Syntaxin 1; D015124:8-Bromo Cyclic Adenosine Monophosphate; D005947:Glucose