Histone removal in sperm protects paternal chromosomes from premature division at fertilization.

The global replacement of histones with protamines in sperm chromatin is widespread in animals, including insects, but its actual function remains enigmatic. We show that in the Drosophila paternal effect mutant paternal loss (pal), sperm chromatin retains germline histones H3 and H4 genome wide without impairing sperm viability. However, after fertilization, pal sperm chromosomes are targeted by the egg chromosomal passenger complex and engage into a catastrophic premature division in synchrony with female meiosis II. We show that pal encodes a rapidly evolving transition protein specifically required for the eviction of (H3-H4)2 tetramers from spermatid DNA after the removal of H2A-H2B dimers. Our study thus reveals an unsuspected role of histone eviction from insect sperm chromatin: safeguarding the integrity of the male pronucleus during female meiosis.

Paternal genome elimination: patterns and mechanisms of drive and silencing.

In thousands of arthropod species, males inherit, but subsequently eliminate the entire haploid genome of their father. However, why this peculiar reproductive strategy evolved repeatedly across diverse species and what mechanisms are involved in paternal genome elimination (PGE) remains largely unknown. In this review, we summarize what we know about the patterns of paternal chromosome elimination during various stages of development in the diverse taxa that have been studied. We also discuss some other unusual features often associated with PGE, such as the transcriptional silencing of paternally derived chromosomes in males and sex determination through the early embryonic elimination of X chromosomes. Little is known about the molecular mechanisms underlying the parent-of-origin-dependent chromosome elimination and silencing under PGE, but we discuss the insight of several studies that are pioneering this work and highlight directions for future research.

Essential and recurrent roles for hairpin RNAs in silencing de novo sex chromosome conflict in Drosophila simulans.

Meiotic drive loci distort the normally equal segregation of alleles, which benefits their own transmission even in the face of severe fitness costs to their host organism. However, relatively little is known about the molecular identity of meiotic drivers, their strategies of action, and mechanisms that can suppress their activity. Here, we present data from the fruitfly Drosophila simulans that address these questions. We show that a family of de novo, protamine-derived X-linked selfish genes (the Dox gene family) is silenced by a pair of newly emerged hairpin RNA (hpRNA) small interfering RNA (siRNA)-class loci, Nmy and Tmy. In the w[XD1] genetic background, knockout of nmy derepresses Dox and MDox in testes and depletes male progeny, whereas knockout of tmy causes misexpression of PDox genes and renders males sterile. Importantly, genetic interactions between nmy and tmy mutant alleles reveal that Tmy also specifically maintains male progeny for normal sex ratio. We show the Dox loci are functionally polymorphic within D. simulans, such that both nmy-associated sex ratio bias and tmy-associated sterility can be rescued by wild-type X chromosomes bearing natural deletions in different Dox family genes. Finally, using tagged transgenes of Dox and PDox2, we provide the first experimental evidence Dox family genes encode proteins that are strongly derepressed in cognate hpRNA mutants. Altogether, these studies support a model in which protamine-derived drivers and hpRNA suppressors drive repeated cycles of sex chromosome conflict and resolution that shape genome evolution and the genetic control of male gametogenesis.

Distinct spermiogenic phenotypes underlie sperm elimination in the Segregation Distorter meiotic drive system.

Segregation Distorter (SD) is a male meiotic drive system in Drosophila melanogaster. Males heterozygous for a selfish SD chromosome rarely transmit the homologous SD+ chromosome. It is well established that distortion results from an interaction between Sd, the primary distorting locus on the SD chromosome and its target, a satellite DNA called Rsp, on the SD+ chromosome. However, the molecular and cellular mechanisms leading to post-meiotic SD+ sperm elimination remain unclear. Here we show that SD/SD+ males of different genotypes but with similarly strong degrees of distortion have distinct spermiogenic phenotypes. In some genotypes, SD+ spermatids fail to fully incorporate protamines after the removal of histones, and degenerate during the individualization stage of spermiogenesis. In contrast, in other SD/SD+ genotypes, protamine incorporation appears less disturbed, yet spermatid nuclei are abnormally compacted, and mature sperm nuclei are eventually released in the seminal vesicle. Our analyses of different SD+ chromosomes suggest that the severity of the spermiogenic defects associates with the copy number of the Rsp satellite. We propose that when Rsp copy number is very high (> 2000), spermatid nuclear compaction defects reach a threshold that triggers a checkpoint controlling sperm chromatin quality to eliminate abnormal spermatids during individualization.

A Role for Caenorhabditis elegans COMPASS in Germline Chromatin Organization.

Deposition of histone H3 lysine 4 (H3K4) methylation at promoters is catalyzed by the SET1/COMPASS complex and is associated with context-dependent effects on gene expression and local changes in chromatin organization. The role of SET1/COMPASS in shaping chromosome architecture has not been investigated. Here we used Caenorhabditis elegans to address this question through a live imaging approach and genetic analysis. Using quantitative FRET (Förster resonance energy transfer)-based fluorescence lifetime imaging microscopy (FLIM) on germ cells expressing histones eGFP-H2B and mCherry-H2B, we find that SET1/COMPASS influences meiotic chromosome organization, with marked effects on the close proximity between nucleosomes. We further show that inactivation of set-2, encoding the C. elegans SET1 homologue, or CFP-1, encoding the chromatin targeting subunit of COMPASS, enhances germline chromosome organization defects and sterility of condensin-II depleted animals. set-2 loss also aggravates germline defects resulting from conditional inactivation of topoisomerase II, another structural component of chromosomes. Expression profiling of set-2 mutant germlines revealed only minor transcriptional changes, suggesting that the observed effects are at least partly independent of transcription. Altogether, our results are consistent with a role for SET1/COMPASS in shaping meiotic chromosomes in C. elegans, together with the non-histone proteins condensin-II and topoisomerase. Given the high degree of conservation, our findings expand the range of functions attributed to COMPASS and suggest a broader role in genome organization in different species.

Spinal-pelvic orientation: potential effect on the diagnosis of spondyloarthritis.

OBJECTIVE: To assess associations of spinal-pelvic orientation with clinical and imaging-study findings suggesting axial SpA (axSpA) in patients with recent-onset inflammatory back pain. METHODS: Spinal-pelvic orientation was assessed in DESIR cohort patients with recent-onset inflammatory back pain and suspected axSpA, by using lateral lumbar-spine radiographs to categorize sacral horizontal angle (<40° vs ⩾40°), lumbosacral angle (<15° vs ⩾15°) and lumbar lordosis (LL, <50° vs ⩾50°). Associations between these angle groups and variables collected at baseline and 2 years later were assessed using the χ2 test (or Fisher's exact) and the Mann-Whitney test. With Bonferroni's correction, P < 0.001 indicated significant differences. RESULTS: Of 362 patients, 358, 356 and 357 had available sacral horizontal angle, lumbosacral angle and LL values, respectively; means were 39.3°, 14.6° and 53.0°, respectively. The prevalence of sacroiliitis on both radiographs and MRI was higher in the LL < 50° group than in the LL ⩾50° group, but the difference was not statistically significant. Clinical presentation and confidence in a diagnosis of axSpA did not differ across angle groups. No significant differences were identified for degenerative changes according to sacral horizontal angle, lumbosacral angle or LL. CONCLUSION: Spinal-pelvic balance was not statistically associated with the clinical or imaging-study findings suggesting axSpA in patients with recent-onset inflammatory back pain.

Association of lumbosacral transitional vertebra and sacroiliitis in patients with inflammatory back pain suggesting axial spondyloarthritis.

OBJECTIVE: Lumbosacral transitional vertebras (LSTVs) are common in the general population, but their potential impact on the sacroiliac joints is unclear. We aimed to determine the prevalence of LSTVs and to assess their associations with sacroiliitis by standard radiography and MRI in a population with suspected axial spondyloarthritis. METHODS: The data were from the DESIR cohort of 688 patients aged 18-50 years with inflammatory low back pain for ⩾3 months but <3 years suggesting axial spondyloarthritis. The baseline pelvic radiographs were read by two blinded readers for the presence and type (Castellvi classification) of LSTVs. Associations between LSTVs and other variables collected at baseline and at the diagnosis were assessed using the χ2 test (or Fisher's exact test) or the Mann-Whitney test. RESULTS: LSTV was found in 200/688 (29.1%) patients. Castellvi type was Ia in 54 (7.8%), Ib in 76 (11.0%), IIa in 20 (2.9%), IIb in 12 (1.7%), IIIa in 7 (1.0%), IIIb in 21 (3.0%) and IV in 10 (1.4%) patients. Compared with the group without LSTVs, the group with LSTVs had higher proportions of patients meeting modified New York criteria for radiographic sacroiliitis (19% vs 27%, respectively; P = 0.013) and Assessment of SpondyloArthritis international Society MRI criteria for sacroiliitis (29% vs 39%, respectively; P = 0.019). CONCLUSION: In patients with inflammatory back pain suggesting axial spondyloarthritis, LSTVs are associated with both radiographic and MRI sacroiliitis.

Physical and functional interaction between SET1/COMPASS complex component CFP-1 and a Sin3S HDAC complex in C. elegans.

The CFP1 CXXC zinc finger protein targets the SET1/COMPASS complex to non-methylated CpG rich promoters to implement tri-methylation of histone H3 Lys4 (H3K4me3). Although H3K4me3 is widely associated with gene expression, the effects of CFP1 loss vary, suggesting additional chromatin factors contribute to context dependent effects. Using a proteomics approach, we identified CFP1 associated proteins and an unexpected direct link between Caenorhabditis elegans CFP-1 and an Rpd3/Sin3 small (SIN3S) histone deacetylase complex. Supporting a functional connection, we find that mutants of COMPASS and SIN3 complex components genetically interact and have similar phenotypic defects including misregulation of common genes. CFP-1 directly binds SIN-3 through a region including the conserved PAH1 domain and recruits SIN-3 and the HDA-1/HDAC subunit to H3K4me3 enriched promoters. Our results reveal a novel role for CFP-1 in mediating interaction between SET1/COMPASS and a Sin3S HDAC complex at promoters.

Peripheral-blood b-cell subset disturbances in inflammatory joint diseases induced by Tropheryma whipplei.

OBJECTIVE: To look for abnormalities in circulating B-cell subsets in patients with rheumatic symptoms of Whipple's disease (WD). METHOD: Consecutive patients seen between 2010 and 2016 for suspected inflammatory joint disease were identified retrospectively. Results of standardized immunological and serological tests and of peripheral-blood B-cell and T-cell subset analysis by flow cytometry were collected. Patients with criteria suggesting WD underwent PCR testing for Tropheryma whipplei, and those with diagnosis of WD (cases) were compared to those without diagnosis (controls). We used ROC curve analysis to evaluate the diagnostic value of flow cytometry findings for WD. RESULTS: Among 2917 patients seen for suspected inflammatory joint disease, 121 had suspected WD, including 9 (9/121, 7.4%) confirmed WD. Proportions of T cells and NK cells were similar between suspected and confirmed WD, whereas cases had a lower proportion of circulating memory B cells (IgD-CD38low, 18.0%±9.7% vs. 26.0%±14.2%, P = 0.041) and higher ratio of activated B cells over memory B cells (4.4±2.0 vs. 2.9±2.2, P = 0.023). Among peripheral-blood B-cells, the proportion of IgD+CD27- naive B cells was higher (66.2%±18.2% vs. 54.6%±18.4%, P = 0.047) and that of IgD-CD27+ switched memory B cells lower (13.3%±5.7% vs. 21.4%±11.9%, P = 0.023), in cases vs. controls. The criterion with the best diagnostic performance was a proportion of IgD+CD27- naive B cells above 70.5%, which had 73% sensitivity and 80% specificity. CONCLUSION: Our study provides data on peripheral-blood B-cell disturbances that may have implications for the diagnosis and pathogenetic understanding of WD.

Usefulness of polymerase chain reaction for diagnosing Whipple's disease in rheumatology.

OBJECTIVES: To determine when Tropheryma whipplei polymerase chain reaction (PCR) is appropriate in patients evaluated for rheumatological symptoms. METHODS: In a retrospective observational study done in rheumatology units of five hospitals, we assessed the clinical and radiological signs that prompted T. whipplei PCR testing between 2010 and 2014, the proportion of patients diagnosed with Whipple's disease, the number of tests performed and the number of diagnoses according to the number of tests, the patterns of Whipple's disease, and the treatments used. Diagnostic ascertainment was based on 1- Presence of at least one suggestive clinical finding; 2- at least one positive PCR test, and 3- a response to antibiotic therapy described by the physician as dramatic, including normalization of C Reactive Protein. RESULTS: At least one PCR test was performed in each of 267 patients. Rheumatic signs were peripheral arthralgia (n = 239, 89%), peripheral arthritis (n = 173, 65%), and inflammatory back pain (n = 85, 32%). Whipple's disease was diagnosed in 13 patients (4.9%). The more frequently positive tests were saliva and stool. In the centres with no diagnoses of Whipple's disease, arthritis was less common and constitutional symptoms more common. The group with Whipple's disease had a higher proportion of males, older age, and greater frequency of arthritis. The annual incidence ranged across centres from 0 to 3.6/100000 inhabitants. CONCLUSION: Males aged 40-75 years with unexplained intermittent seronegative peripheral polyarthritis, including those without constitutional symptoms, should have T. whipplei PCR tests on saliva, stool and, if possible, joint fluid.