Hybrid dysgenesis in Drosophila: the mechanism of T-007-induced male recombination

Polymorphism in BACH2 gene is a marker of polyglandular autoimmunity

PURPOSE

Genetically predisposed individuals may develop several autoimmune diseases-autoimmune polyendocrine syndromes (APS). APS types 2-4, are complex disorders, which combine various organ-specific autoimmune conditions. Recent reports support the considerable role of the BACH2 gene in immune cell differentiation and shifting the T-cell balance towards regulatory T-cells. BACH2 polymorphisms are associated with autoimmune disorders, including Addison's disease (AD), Graves' disease (GD), and probably type 1 diabetes (T1D). Our study was aimed to investigate the BACH2 variant, rs3757247, in endocrine autoimmunity in the Polish population.

METHODS

The analysis comprised 346 individuals with APS, 387 with T1D only, and 568 controls. Genotyping was performed using TaqMan chemistry.

RESULTS

APS type 2 was found in 219 individuals, type 3 in 102, and type 4 in 25 subjects. Overall, AD was diagnosed in 244 subjects, Hashimoto's thyroiditis-in 238, T1D-in 127, GD-in 58, vitiligo and chronic gastritis each in 40 patients, celiac disease-in 28, premature menopause in 18, and alopecia in 4 patients. Minor T allele at rs3757247 was found in 56.4% APS vs. 44.1% control alleles (OR 1.59; 95%CI: 1.30-1.95, p < 0.0001). The distribution of genotypes revealed excess TT homozygotes in the APS cohort (33.2 vs. 20.1% in controls, p < 0.0001). The frequencies of rs3757247 alleles and genotypes in T1D patients did not present significant differences vs. controls (p-values > 0.05).

CONCLUSIONS

These results provide evidence of the association between BACH2 polymorphism and polyglandular autoimmunity. Since carriers of rs3757247 display increased risk for additional autoimmune conditions, this variant could identify individuals prone to develop APS.

Hybrid dysgenesis in Drosophila virilis results in clusters of mitotic recombination and loss-of-heterozygosity but leaves meiotic recombination unaltered

BACKGROUND

Transposable elements (TEs) are endogenous mutagens and their harmful effects are especially evident in syndromes of hybrid dysgenesis. In Drosophila virilis, hybrid dysgenesis is a syndrome of incomplete gonadal atrophy that occurs when males with multiple active TE families fertilize females that lack active copies of the same families. This has been demonstrated to cause the transposition of paternally inherited TE families, with gonadal atrophy driven by the death of germline stem cells. Because there are abundant, active TEs in the male inducer genome, that are not present in the female reactive genome, the D. virilis syndrome serves as an excellent model for understanding the effects of hybridization between individuals with asymmetric TE profiles.

RESULTS

Using the D. virilis syndrome of hybrid dysgenesis as a model, we sought to determine how the landscape of germline recombination is affected by parental TE asymmetry. Using a genotyping-by-sequencing approach, we generated a high-resolution genetic map of D. virilis and show that recombination rate and TE density are negatively correlated in this species. We then contrast recombination events in the germline of dysgenic versus non-dysgenic F1 females to show that the landscape of meiotic recombination is hardly perturbed during hybrid dysgenesis. In contrast, hybrid dysgenesis in the female germline increases transmission of chromosomes with mitotic recombination. Using a de novo PacBio assembly of the D. virilis inducer genome we show that clusters of mitotic recombination events in dysgenic females are associated with genomic regions with transposons implicated in hybrid dysgenesis.

CONCLUSIONS

Overall, we conclude that increased mitotic recombination is likely the result of early TE activation in dysgenic progeny, but a stable landscape of meiotic recombination indicates that either transposition is ameliorated in the adult female germline or that regulation of meiotic recombination is robust to ongoing transposition. These results indicate that the effects of parental TE asymmetry on recombination are likely sensitive to the timing of transposition.

Bar reversion and hybrid dysgenesis inDrosophila melanogaster:reversion in males and in inversions

The effect of the P-M system of hybrid dysgenesis inDrosophila melanogasteron unequal crossing-over was studied using the Bar duplication. This system of dysgenesis had no demonstrable effect on the rate of Bar reversion. In the course of the study it was found that there was a greatly reduced rate of reversion in two homozygous inversion stocks. Further, one revertant was found which may result from unequal crossing over at the Bar locus in males.

P-element transposase induces male recombination in Drosophila melanogaster

Male recombination in P-M dysgenic crosses has been viewed as a reflection of P-element transposase interacting with P elements. However, recent studies suggest that the transposase may catalyse double-stranded breaks in chromosomal DNA. We have, therefore, introduced P(delta 2-3 ry+) (99B), a single non-mobile P-element transposase source, into the long-standing laboratory true M strains of a flanking lethal crossover selective system, thus facilitating the examination of rare male recombination events as an assay for transposase activity. We find that the rate of male recombination in the presence of this non-mobile P element is greater than twenty times the background rate of male recombination in the control examined prior to introduction of the transposase source.