High-density linkage maps and chromosome level genome assemblies unveil direction and frequency of extensive structural rearrangements in wood white butterflies (Leptidea spp.).

Karyotypes are generally conserved between closely related species and large chromosome rearrangements typically have negative fitness consequences in heterozygotes, potentially driving speciation. In the order Lepidoptera, most investigated species have the ancestral karyotype and gene synteny is often conserved across deep divergence, although examples of extensive genome reshuffling have recently been demonstrated. The genus Leptidea has an unusual level of chromosome variation and rearranged sex chromosomes, but the extent of restructuring across the rest of the genome is so far unknown. To explore the genomes of the wood white (Leptidea) species complex, we generated eight genome assemblies using a combination of 10X linked reads and HiC data, and improved them using linkage maps for two populations of the common wood white (L. sinapis) with distinct karyotypes. Synteny analysis revealed an extensive amount of rearrangements, both compared to the ancestral karyotype and between the Leptidea species, where only one of the three Z chromosomes was conserved across all comparisons. Most restructuring was explained by fissions and fusions, while translocations appear relatively rare. We further detected several examples of segregating rearrangement polymorphisms supporting a highly dynamic genome evolution in this clade. Fusion breakpoints were enriched for LINEs and LTR elements, which suggests that ectopic recombination might be an important driver in the formation of new chromosomes. Our results show that chromosome count alone may conceal the extent of genome restructuring and we propose that the amount of genome evolution in Lepidoptera might still be underestimated due to lack of taxonomic sampling.

Induction of experimental arthritis in BALB/c mice by inclusion of a foreign protein in the collagen inoculum.

The susceptibility of mice to collagen-induced arthritis (CIA) has, among other things, been linked to the major histocompatibility complex class II genes as well as other genes. This study was designed to examine the possibilities to establish CIA in low susceptible I-Ad (Balb/C) mice. Balb/C mice were immunized twice with bovine type II collagen (BCII) in complete Freund's adjuvant (CFA) containing the amount of Mycobacterium tuberculosis needed to induce CIA in low susceptible I-Ab (C57BL/6) mice. Some mice received the conceivable arthritogenic inoculum mixed with ovalbumin (OVA). Clinical arthritis was monitored. Antibody activity and T-cell reactivity to BCII were determined. Unexpectedly, only mice that were immunized with the BCII-OVA mixture developed arthritis. Combining BCII with another foreign protein, keyhole limpet hemocyanin, but not the self-protein mouse serum albumin, also triggered arthritis. Prior to the appearance of arthritis the serum levels of IgG autoantibodies to BCII were higher in the coimmunized mice than in the mice that were immunized with BCII alone. Yet, splenocytes stimulated in vitro with BCII did not proliferate or produce interferon-gamma. Immunization of Balb/c mice with an emulsion-containing CFA and BCII mixed with a foreign body, but not a self-protein, elevates the level of circulating autoantibodies to CII and subsequently induces arthritis.

Bystander suppression of collagen-induced arthritis in mice fed ovalbumin.

We wanted to assess whether B-cell and/or T-cell responses to collagen and thereby the course of collagen-induced arthritis could be suppressed by regulatory mechanisms associated with oral tolerance to an unrelated protein. DBA/1 mice were fed ovalbumin (OVA)-containing pellets ad libitum for 1 week and subsequently coimmunized twice, with a mixture of bovine collagen type II (BCII) and OVA in Freund's complete adjuvant. Mice fed OVA before coimmunization with BCII and OVA had significantly lower arthritic scores than mice immunized with BCII only. Their body weight increased during the study period and their anti-BCII antibody activity was significantly IgG2a lower. The frequency of spleen cells producing IgG anti-BCII antibody was also reduced. Coimmunization per se slightly ameliorated the development of arthritis, resulting in an early, transient reduction. It resulted in significantly higher IgG1 anti-BCII antibody activity and increased splenocyte secretion of IFN-gamma and IL-10 in response to BCII. Our findings demonstrate that OVA-specific regulatory events induced by feeding OVA, i.e. bystander suppression, reduced the severity of arthritis in animals immunized with BCII and OVA. Anti-BCII specific antibody responses and cytokine secretion by types 1 and 2 T helper cells were also decreased.