Immune reactivity of diabetes-associated human monoclonal autoantibodies defines multiple epitopes and detects two domain boundaries in glutamate decarboxylase

Autoreactive islet cell Abs (ICA) accompany the pathogenic destruction of pancreatic beta cells in insulin-dependent diabetes mellitus (IDDM). Human monoclonal ICA (MICA 1-6), previously derived from a DR1/DR7-positive newly diagnosed diabetic patient, recognized the islet cell autoantigen glutamate decarboxylase 65 (GAD65) and defined two distinct conformational (MICA 1/3 and MICA 4/6) and one linear (MICA 2) autoimmune epitopes in this molecule. We have isolated 4 new ICA-reactive B cell lines, one from a DR4/DR11-positive newly diagnosed IDDM patient (MICA 7) and three from a DR3 homozygous patient with both IDDM and Graves' disease (MICA 8-10). Like MICA 1-6, MICA 7-10 are specific for GAD65, suggesting that GAD65-reactive B cells dominate the ICA response in IDDM. Comparative analysis of MICA 1-6 and MICA 7-10, using GAD65 mutants and blocking experiments, showed that MICA 7-10 define three novel conformational autoimmune epitopes in GAD65. Further structural analysis of the MICA 1-10 epitopes revealed two distinct and one overlapping region of epitope clusters. Thus, the C-terminal region, defined by amino acids 450 to 570, harbors the conformational MICA1/3 and MICA 7 epitopes as well as the linear epitope of MICA 2 (amino acids 506-531). The MICA 4/6 and MICA 10 epitopes are located in the middle region of the molecule defined by amino acids 245 to 449, whereas the N-terminal region contributes only to the MICA 8/9 epitopes (encompassed in amino acids 39-585). MICA 1-6, 7, and 8-10, derived from three IDDM patients of different HLA haplotypes, define six different epitopes in GAD65 and represent tools to determine the spectrum, possible HLA association, and temporal order of epitope recognition in IDDM

In the platypus a meiotic chain of ten sex chromosomes shares genes with the bird Z and mammal X chromosomes

Two centuries after the duck-billed platypus was discovered, monotreme chromosome systems remain deeply puzzling. Karyotypes of males1, or of both sexes2–4, were claimed to contain several unpaired chromosomes (including the X chromosome) that form a multi-chromosomal chain at meiosis. Such meiotic chains exist in plants5 and insects6 but are rare in vertebrates7. How the platypus chromosome system works to determine sex and produce balanced gametes has been controversial for decades1– 4. Here we demonstrate that platypus have five malespecific chromosomes (Y chromosomes) and five chromosomes present in one copy in males and two copies in females (X chromosomes). These ten chromosomes form a multivalent chain at male meiosis, adopting an alternating pattern to segregate into XXXXX-bearing and YYYYY-bearing sperm. Which, if any, of these sex chromosomes bears one or more sex-determining genes remains unknown. The largest X chromosome, with homology to the human X chromosome, lies at one end of the chain, and a chromosome with homology to the bird Z chromosome lies near the other end. This suggests an evolutionary link between mammal and bird sex chromosome systems, which were previously thought to have evolved independently.Frank Grützner, Willem Rens, Enkhjargal Tsend-Ayush, Nisrine El-Mogharbel, Patricia C. M. O'Brien, Russell C. Jones, Malcolm A. Ferguson-Smith and Jennifer A. Marshall Grave