Aims. Our goal was to identify genetic variants that determine the response to insulin resistance and hyperglycaemia. This report documents the diabetes syndrome of two new congenic strains of mice generated by the transfer of the Lepr db mutation to the FVB/NJ strain and the Lep ob mutation to the DBA/2J strain. Methods. Mice were characterised by measures of blood metabolites and hormones along with challenges with glucose and insulin injections. Histological examinations of the endocrine pancreas and the kidneys were also carried out. Results. Obese mice of the FVB-db congenic strain show long-term hyperglycaemia that is primarily due to severe insulin resistance. The hyperglycaemia in the fed state persists despite escalating secretion of insulin and massive increase of pancreatic beta cells. Obese FVB-db mice show evidence of mesangial matrix expansion, a hallmark of diabetic nephropathy.Leptin-deficient mice of the DBA-ob strain have variable obesity-diabetes. In mice with high insulin (>10 ng/ml), DBA-ob/ob mice maintain their increased adiposity and have a large increase in betacell number. In mice with low insulin (<1 ng/ml) DBA-ob/ob mice have greatly diminished adiposity. These mice have atrophied islets with evidence of increased beta-cell neogenesis from the ductal epithelium. Conclusions. The strain-specific responses suggest the existence of genetic variants that control insulin sensitivity and beta-cell responses in the strains described in this report. These new models of obesity-diabetes should prove useful in dissecting the genetic control of beta-cell responses to hyperglycaemia and insulin resistance. [Diabetologia (2002) [6,7], SHR [8], and LA [9]. In rats, it seems that only obese males are subject to developing severe hyperglycaemia and contraction of beta-cell numbers.The loss of beta cells in these obesity-diabetes models is not mediated by the immune system. Studies have shown that C57BLKS/J db/db (K-db) mice develop their characteristic diabetes phenotype independent of a functional immune system [10]. The response of the beta cell in these obese rodents is subject to dietary influences. When placed on a completely carbohydrate-free diet (CHO-free diet), obese C57BLKS/J db/db mice are able to maintain near-euglycaemia and preserve their pancreatic beta-cell mass [11].While these strain-specific phenotypes have been documented [4], some of the congenic strains have been lost. This report describes the generation and characterisation of several new congenic mouse strains carrying mutations of Lep or Lepr. The FVB congenic strains (FVB-db and FVB-ob) provide a new diabetes phenotype that has not been described previously. Obese FVB mice suffer a prolonged period of hyperglycaemia that produces massive expansion of beta-cell mass. We show data that the early onset of severe insulin resistance probably accounts for the hyperglycaemia of these strains. The islet hyperplasia of obese FVB mice suggests that prolonged hyperglycaemia does not eventually lead to complete betacell atro...

IA-2 and IA-2 beta are major autoantigens in insulin-dependent diabetes mellitus (IDDM) and the precursors, respectively, of a 40-and 37-kDa tryptic fragment that reacts with IDDM sera. In the present study, by amino acid sequencing of recombinant IA-2 and IA-2 beta, we determined the tryptic cleavage sites involved in the generation of these fragments. Both cleavage sites are immediately after an arginine residue at position 653 for IA-2 and position 679 for IA-2 beta. The resulting tryptic fragments are 326 and 307 amino acids in length and retain their ability to react with IDDM sera. In contrast to IA-2 and IA-2 beta, other members of the protein tyrosine phosphatase (PTP) family (i.e., RPTP kappa, RPTPmu, NU-3, SHP, and 3CH134) are completely susceptible to digestion by trypsin. Sequence analysis revealed five conserved cysteine residues in IA-2 and IA-2 beta that are not present in other PTPs. Reduction and alkylation of IA-2 and IA-2 beta recombinant proteins resulted in loss of both resistance to digestion by trypsin and reactivity with autoantibodies in IDDM sera. It is concluded that disulfide bond formation plays a critical role in the maintenance of antigenic structure and that the autoantibodies to IA-2/IA-2 beta in IDDM sera recognize conformational epitopes.