The chiral structure of porous chitin within the wing-scales of Callophrys rubi.

The structure of the porous three-dimensional reticulated pattern in the wing scales of the butterfly Callophrys rubi (the Green Hairstreak) is explored in detail, via scanning and transmission electron microscopy. A full 3D tomographic reconstruction of a section of this material reveals that the predominantly chitin material is assembled in the wing scale to form a structure whose geometry bears a remarkable correspondence to the srs net, well-known in solid state chemistry and soft materials science. The porous solid is bounded to an excellent approximation by a parallel surface to the Gyroid, a three-periodic minimal surface with cubic crystallographic symmetry I4132, as foreshadowed by Stavenga and Michielson. The scale of the structure is commensurate with the wavelength of visible light, with an edge of the conventional cubic unit cell of the parallel-Gyroid of approximately 310 nm. The genesis of this structure is discussed, and we suggest it affords a remarkable example of templating of a chiral material via soft matter, analogous to the formation of mesoporous silica via surfactant assemblies in solution. In the butterfly, the templating is achieved by the lipid-protein membranes within the smooth endoplasmic reticulum (while it remains in the chrysalis), that likely form cubic membranes, folded according to the form of the Gyroid. The subsequent formation of the chiral hard chitin framework is suggested to be driven by the gradual polymerisation of the chitin precursors, whose inherent chiral assembly in solution (during growth) promotes the formation of a single enantiomer.

Recombination signature of germline immunoglobulin variable genes.

In human and mouse, the germline contains a tandem array of highly homologous variable (V) gene elements which encode part of the antigen-binding region of the antibody protein. During evolution this array apparently arose by gene duplication followed by diversification of duplicated genes via point mutation and recombination. Analysis of germline V gene sequences using a novel algorithm shows that major recombination sites coincide with the borders of the leader intron and the cap site, consistent with the hypothesis that over evolutionary time cDNA derived by reverse transcription of pre-mRNA in B lymphocytes has recombined with germline DNA.

Impaired antigen presentation by murine I-Ad class II MHC molecules expressed in normal and HLA-DM-defective human B cell lines.

The inability of certain antigen processing mutant cell lines to present intact proteins to T cells and to form SDS-stable MHC class II dimers has been shown to result from defective expression of HLA-encoded DMA and DMB genes. We have utilized some of these mutants to determine species compatibility of antigen presentation components. Mouse MHC class II I-Ad cDNA was transfected into the human B cell lymphoblastoid cell lines 8.1.6, 7.9.6 (a mutant cell line derived from 8.1.6) and an independent deletion mutant T2 (called 8.1.6d, 7.9.6d and T2.d respectively). These cells were than examined for various functions in antigen presentation. Interestingly, none of the cells transfected with I-Ad presented peptides derived from intact proteins to specific T cell hybridomas. However, presentation of synthetic peptides by these cells was normal. The ability to form SDS-stable dimers was dramatically reduced in the transfectants. In addition, I-Ad molecules at the cell surface appeared loaded predominantly with the invariant chain peptides, CLIP. These properties of the I-Ad transfectants are identical to those described for HLA class II molecules expressed in HLA-DM mutants. Perhaps the most interesting finding was the inability of I-Ad in 8.1.6 to present protein antigens. Since 8.1.6 cells present antigens to HLA-DR, DP, DQ-restricted T cells and also have intact HLA-DM and invariant chain (II) functions, these results argue that some component of human antigen processing machinery is incompatible with I-Ad molecules.