Epigenetic dynamics of centromeres and neocentromeres in Cryptococcus deuterogattii

Deletion of native centromeres in the human fungal pathogen Cryptococcus deuterogattii leads to neocentromere formation. Native centromeres span truncated transposable elements, while neocentromeres do not and instead span actively expressed genes. To explore the epigenetic organization of neocentromeres, we analyzed the distribution of the heterochromatic histone modification H3K9me2, 5mC DNA methylation and the euchromatin mark H3K4me2. Native centromeres are enriched for both H3K9me2 and 5mC DNA methylation marks and are devoid of H3K4me2, while neocentromeres do not exhibit any of these features. Neocentromeres in cen10Δ mutants are unstable and chromosome-chromosome fusions occur. After chromosome fusion, the neocentromere is inactivated and the native centromere of the chromosome fusion partner remains as the sole, active centromere. In the present study, the active centromere of a fused chromosome was deleted to investigate if epigenetic memory promoted the re-activation of the inactive neocentromere. Our results show that the inactive neocentromere is not re-activated and instead a novel neocentromere forms directly adjacent to the deleted centromere of the fused chromosome. To study the impact of transcription on centromere stability, the actively expressed URA5 gene was introduced into the CENP-A bound regions of a native centromere. The introduction of the URA5 gene led to a loss of CENP-A from the native centromere, and a neocentromere formed adjacent to the native centromere location. Remarkably, the inactive, native centromere remained enriched for heterochromatin, yet the integrated gene was expressed and devoid of H3K9me2. A cumulative analysis of multiple CENP-A distribution profiles revealed centromere drift in C. deuterogattii, a previously unreported phenomenon in fungi. The CENP-A-binding shifted within the ORF-free regions and showed a possible association with a truncated transposable element. Taken together, our findings reveal that neocentromeres in C. deuterogattii are highly unstable and are not marked with an epigenetic memory, distinguishing them from native centromeres.

Linear eukaryotic chromosomes require a specific chromosomal region, the centromere, where the macromolecular kinetochore protein complex assembles. In most organisms, centromeres are located in gene-free, repeat-rich chromosomal regions and may or may not be associated with heterochromatic epigenetic marks. We report that the native centromeres of the human fungal pathogen Cryptococcus deuterogattii are enriched with heterochromatin marks. Deleting a centromere in C. deuterogattii results in formation of neocentromeres that span genes. In some cases, neocentromeres are unstable leading to chromosome-chromosome fusions and neocentromere inactivation. These neocentromeres, unlike native centromeres, lack any of the tested heterochromatic marks or any epigenetic memory. We also found that neocentromere formation can be triggered not only by deletion of the native centromere but also by disrupting its function via insertion of a gene. These results show that neocentromere dynamics in this fungal pathogen are unique among organisms studied so far. Our results also revealed key differences between epigenetics of native centromeres between C. deuterogattii and its sister species, C. neoformans. These finding provide an opportunity to test and study the evolution of centromeres, as well as neocentromeres, in this species complex and how it might contribute to their genome evolution.

Ago1 Affects the Virulence of the Fungal Plant Pathogen Zymoseptoria tritici

In host-pathogen interactions RNA interference (RNAi) has emerged as a pivotal mechanism to modify both, the immune responses of the host as well as the pathogenicity and virulence of the pathogen. In addition, in some fungi RNAi is also known to affect chromosome biology via its effect on chromatin conformation. Previous studies reported no effect of the RNAi machinery on the virulence of the fungal plant pathogen Zymoseptoria tritici however the role of RNAi is still poorly understood in this species. Herein, we elucidate whether the RNAi machinery is conserved within the genus Zymoseptoria. Moreover, we conduct functional analyses of Argonaute and Dicer-like proteins and test if the RNAi machinery affects chromosome stability. We show that the RNAi machinery is conserved among closely related Zymoseptoria species while an exceptional pattern of allelic diversity was possibly caused by introgression. The deletion of Ago1 reduced the ability of the fungus to produce asexual propagules in planta in a quantitative matter. Chromosome stability of the accessory chromosome of Z. tritici was not prominently affected by the RNAi machinery. These results indicate, in contrast to previous finding, a role of the RNAi pathway during host infection, but not in the stability of accessory chromosomes in Z. tritici.

The insertion of a mitochondrial selfish element into the nuclear genome and its consequences

Homing endonucleases (HE) are enzymes capable of cutting DNA at highly specific target sequences, the repair of the generated double-strand break resulting in the insertion of the HE-encoding gene ("homing" mechanism). HEs are present in all three domains of life and viruses; in eukaryotes, they are mostly found in the genomes of mitochondria and chloroplasts, as well as nuclear ribosomal RNAs. We here report the case of a HE that accidentally integrated into a telomeric region of the nuclear genome of the fungal maize pathogen Ustilago maydis. We show that the gene has a mitochondrial origin, but its original copy is absent from the U. maydis mitochondrial genome, suggesting a subsequent loss or a horizontal transfer from a different species. The telomeric HE underwent mutations in its active site and lost its original start codon. A potential other start codon was retained downstream, but we did not detect any significant transcription of the newly created open reading frame, suggesting that the inserted gene is not functional. Besides, the insertion site is located in a putative RecQ helicase gene, truncating the C-terminal domain of the protein. The truncated helicase is expressed during infection of the host, together with other homologous telomeric helicases. This unusual mutational event altered two genes: The integrated HE gene subsequently lost its homing activity, while its insertion created a truncated version of an existing gene, possibly altering its function. As the insertion is absent in other field isolates, suggesting that it is recent, the U. maydis 521 reference strain offers a snapshot of this singular mutational event.

Genome compartmentalization predates species divergence in the plant pathogen genus Zymoseptoria

Background

Antagonistic co-evolution can drive rapid adaptation in pathogens and shape genome architecture. Comparative genome analyses of several fungal pathogens revealed highly variable genomes, for many species characterized by specific repeat-rich genome compartments with exceptionally high sequence variability. Dynamic genome structure may enable fast adaptation to host genetics. The wheat pathogen Zymoseptoria tritici with its highly variable genome, has emerged as a model organism to study genome evolution of plant pathogens. Here, we compared genomes of Z. tritici isolates and of sister species infecting wild grasses to address the evolution of genome composition and structure.

Results

Using long-read technology, we sequenced and assembled genomes of Z. ardabiliae, Z. brevis, Z. pseudotritici and Z. passerinii, together with two isolates of Z. tritici. We report a high extent of genome collinearity among Zymoseptoria species and high conservation of genomic, transcriptomic and epigenomic signatures of compartmentalization. We identify high gene content variability both within and between species. In addition, such variability is mainly limited to the accessory chromosomes and accessory compartments. Despite strong host specificity and non-overlapping host-range between species, predicted effectors are mainly shared among Zymoseptoria species, yet exhibiting a high level of presence-absence polymorphism within Z. tritici. Using in planta transcriptomic data from Z. tritici, we suggest different roles for the shared orthologs and for the accessory genes during infection of their hosts.

Conclusion

Despite previous reports of high genomic plasticity in Z. tritici, we describe here a high level of conservation in genomic, epigenomic and transcriptomic composition and structure across the genus Zymoseptoria. The compartmentalized genome allows the maintenance of a functional core genome co-occurring with a highly variable accessory genome.

Centromere deletion in Cryptococcus deuterogattii leads to neocentromere formation and chromosome fusions

The human fungal pathogen Cryptococcus deuterogattii is RNAi-deficient and lacks active transposons in its genome. C. deuterogattii has regional centromeres that contain only transposon relics. To investigate the impact of centromere loss on the C. deuterogattii genome, either centromere 9 or 10 was deleted. Deletion of either centromere resulted in neocentromere formation and interestingly, the genes covered by these neocentromeres maintained wild-type expression levels. In contrast to cen9∆ mutants, cen10∆ mutant strains exhibited growth defects and were aneuploid for chromosome 10. At an elevated growth temperature (37°C), the cen10∆ chromosome was found to have undergone fusion with another native chromosome in some isolates and this fusion restored wild-type growth. Following chromosomal fusion, the neocentromere was inactivated, and the native centromere of the fused chromosome served as the active centromere. The neocentromere formation and chromosomal fusion events observed in this study in C. deuterogattii may be similar to events that triggered genomic changes within the Cryptococcus/Kwoniella species complex and may contribute to speciation throughout the eukaryotic domain.

Long transposon-rich centromeres in an oomycete reveal divergence of centromere features in Stramenopila-Alveolata-Rhizaria lineages

Centromeres are chromosomal regions that serve as platforms for kinetochore assembly and spindle attachments, ensuring accurate chromosome segregation during cell division. Despite functional conservation, centromere DNA sequences are diverse and often repetitive, making them challenging to assemble and identify. Here, we describe centromeres in an oomycete Phytophthora sojae by combining long-read sequencing-based genome assembly and chromatin immunoprecipitation for the centromeric histone CENP-A followed by high-throughput sequencing (ChIP-seq). P. sojae centromeres cluster at a single focus at different life stages and during nuclear division. We report an improved genome assembly of the P. sojae reference strain, which enabled identification of 15 enriched CENP-A binding regions as putative centromeres. By focusing on a subset of these regions, we demonstrate that centromeres in P. sojae are regional, spanning 211 to 356 kb. Most of these regions are transposon-rich, poorly transcribed, and lack the histone modification H3K4me2 but are embedded within regions with the heterochromatin marks H3K9me3 and H3K27me3. Strikingly, we discovered a Copia-like transposon (CoLT) that is highly enriched in the CENP-A chromatin. Similar clustered elements are also found in oomycete relatives of P. sojae, and may be applied as a criterion for prediction of oomycete centromeres. This work reveals a divergence of centromere features in oomycetes as compared to other organisms in the Stramenopila-Alveolata-Rhizaria (SAR) supergroup including diatoms and Plasmodium falciparum that have relatively short and simple regional centromeres. Identification of P. sojae centromeres in turn also advances the genome assembly.

Oomycetes are fungal-like microorganisms that belong to the stramenopiles within the Stramenopila-Alveolata-Rhizaria (SAR) supergroup. The Phytophthora oomycetes are infamous as plant killers, threatening crop production worldwide. Because of the highly repetitive nature of their genomes, assembly of oomycete genomes presents challenges that impede identification of centromeres, which are chromosomal sites mediating faithful chromosome segregation. We report long-read sequencing-based genome assembly of the Phytophthora sojae reference strain, which facilitated the discovery of centromeres. P. sojae harbors large regional centromeres fully embedded in heterochromatin, and enriched for a Copia-like transposon that is also found in discrete clusters in other oomycetes. This study provides insight into the oomycete genome organization, broadens our knowledge of centromere structure, function and evolution in eukaryotes, and may help elucidate the high frequency of aneuploidy during oomycete reproduction.

Destabilization of chromosome structure by histone H3 lysine 27 methylation

Chromosome and genome stability are important for normal cell function as instability often correlates with disease and dysfunction of DNA repair mechanisms. Many organisms maintain supernumerary or accessory chromosomes that deviate from standard chromosomes. The pathogenic fungus Zymoseptoria tritici has as many as eight accessory chromosomes, which are highly unstable during meiosis and mitosis, transcriptionally repressed, show enrichment of repetitive elements, and enrichment with heterochromatic histone methylation marks, e.g., trimethylation of H3 lysine 9 or lysine 27 (H3K9me3, H3K27me3). To elucidate the role of heterochromatin on genome stability in Z. tritici, we deleted the genes encoding the methyltransferases responsible for H3K9me3 and H3K27me3, kmt1 and kmt6, respectively, and generated a double mutant. We combined experimental evolution and genomic analyses to determine the impact of these deletions on chromosome and genome stability, both in vitro and in planta. We used whole genome sequencing, ChIP-seq, and RNA-seq to compare changes in genome and chromatin structure, and differences in gene expression between mutant and wildtype strains. Analyses of genome and ChIP-seq data in H3K9me3-deficient strains revealed dramatic chromatin reorganization, where H3K27me3 is mostly relocalized into regions that are enriched with H3K9me3 in wild type. Many genome rearrangements and formation of new chromosomes were found in the absence of H3K9me3, accompanied by activation of transposable elements. In stark contrast, loss of H3K27me3 actually increased the stability of accessory chromosomes under normal growth conditions in vitro, even without large scale changes in gene activity. We conclude that H3K9me3 is important for the maintenance of genome stability because it disallows H3K27me3 in regions considered constitutive heterochromatin. In this system, H3K27me3 reduces the overall stability of accessory chromosomes, generating a "metastable" state for these quasi-essential regions of the genome.

Histone modifications rather than the novel regional centromeres of Zymoseptoria tritici distinguish core and accessory chromosomes

BACKGROUND

Supernumerary chromosomes have been found in many organisms. In fungi, these "accessory" or "dispensable" chromosomes are present at different frequencies in populations and are usually characterized by higher repetitive DNA content and lower gene density when compared to the core chromosomes. In the reference strain of the wheat pathogen, Zymoseptoria tritici, eight discrete accessory chromosomes have been found. So far, no functional role has been assigned to these chromosomes; however, they have existed as separate entities in the karyotypes of Zymoseptoria species over evolutionary time. In this study, we addressed what-if anything-distinguishes the chromatin of accessory chromosomes from core chromosomes. We used chromatin immunoprecipitation combined with high-throughput sequencing ("ChIP-seq") of DNA associated with the centromere-specific histone H3, CENP-A (CenH3), to identify centromeric DNA, and ChIP-seq with antibodies against dimethylated H3K4, trimethylated H3K9 and trimethylated H3K27 to determine the relative distribution and proportion of euchromatin, obligate and facultative heterochromatin, respectively.

RESULTS

Centromeres of the eight accessory chromosomes have the same sequence composition and structure as centromeres of the 13 core chromosomes and they are of similar length. Unlike those of most other fungi, Z. tritici centromeres are not composed entirely of repetitive DNA; some centromeres contain only unique DNA sequences, and bona fide expressed genes are located in regions enriched with CenH3. By fluorescence microscopy, we showed that centromeres of Z. tritici do not cluster into a single chromocenter during interphase. We found dramatically higher enrichment of H3K9me3 and H3K27me3 on the accessory chromosomes, consistent with the twofold higher proportion of repetitive DNA and poorly transcribed genes. In contrast, no single histone modification tested here correlated with the distribution of centromeric nucleosomes.

CONCLUSIONS

All centromeres are similar in length and composed of a mixture of unique and repeat DNA, and most contain actively transcribed genes. Centromeres, subtelomeric regions or telomere repeat length cannot account for the differences in transfer fidelity between core and accessory chromosomes, but accessory chromosomes are greatly enriched in nucleosomes with H3K27 trimethylation. Genes on accessory chromosomes appear to be silenced by trimethylation of H3K9 and H3K27.

The Oxytricha trifallax macronuclear genome: a complex eukaryotic genome with 16,000 tiny chromosomes

With more chromosomes than any other sequenced genome, the macronuclear genome of Oxytricha trifallax has a unique and complex architecture, including alternative fragmentation and predominantly single-gene chromosomes.

The macronuclear genome of the ciliate Oxytricha trifallax displays an extreme and unique eukaryotic genome architecture with extensive genomic variation. During sexual genome development, the expressed, somatic macronuclear genome is whittled down to the genic portion of a small fraction (∼5%) of its precursor “silent” germline micronuclear genome by a process of “unscrambling” and fragmentation. The tiny macronuclear “nanochromosomes” typically encode single, protein-coding genes (a small portion, 10%, encode 2–8 genes), have minimal noncoding regions, and are differentially amplified to an average of ∼2,000 copies. We report the high-quality genome assembly of ∼16,000 complete nanochromosomes (∼50 Mb haploid genome size) that vary from 469 bp to 66 kb long (mean ∼3.2 kb) and encode ∼18,500 genes. Alternative DNA fragmentation processes ∼10% of the nanochromosomes into multiple isoforms that usually encode complete genes. Nucleotide diversity in the macronucleus is very high (SNP heterozygosity is ∼4.0%), suggesting that Oxytricha trifallax may have one of the largest known effective population sizes of eukaryotes. Comparison to other ciliates with nonscrambled genomes and long macronuclear chromosomes (on the order of 100 kb) suggests several candidate proteins that could be involved in genome rearrangement, including domesticated MULE and IS1595-like DDE transposases. The assembly of the highly fragmented Oxytricha macronuclear genome is the first completed genome with such an unusual architecture. This genome sequence provides tantalizing glimpses into novel molecular biology and evolution. For example, Oxytricha maintains tens of millions of telomeres per cell and has also evolved an intriguing expansion of telomere end-binding proteins. In conjunction with the micronuclear genome in progress, the O. trifallax macronuclear genome will provide an invaluable resource for investigating programmed genome rearrangements, complementing studies of rearrangements arising during evolution and disease.

The macronuclear genome of the ciliate Oxytricha trifallax, contained in its somatic nucleus, has a unique genome architecture. Unlike its diploid germline genome, which is transcriptionally inactive during normal cellular growth, the macronuclear genome is fragmented into at least 16,000 tiny (∼3.2 kb mean length) chromosomes, most of which encode single actively transcribed genes and are differentially amplified to a few thousand copies each. The smallest chromosome is just 469 bp, while the largest is 66 kb and encodes a single enormous protein. We found considerable variation in the genome, including frequent alternative fragmentation patterns, generating chromosome isoforms with shared sequence. We also found limited variation in chromosome amplification levels, though insufficient to explain mRNA transcript level variation. Another remarkable feature of Oxytricha's macronuclear genome is its inordinate fondness for telomeres. In conjunction with its possession of tens of millions of chromosome-ending telomeres per macronucleus, we show that Oxytricha has evolved multiple putative telomere-binding proteins. In addition, we identified two new domesticated transposase-like protein classes that we propose may participate in the process of genome rearrangement. The macronuclear genome now provides a crucial resource for ongoing studies of genome rearrangement processes that use Oxytricha as an experimental or comparative model.

The Oxytricha trifallax mitochondrial genome

The Oxytricha trifallax mitochondrial genome contains the largest sequenced ciliate mitochondrial chromosome (~70 kb) plus a ~5-kb linear plasmid bearing mitochondrial telomeres. We identify two new ciliate split genes (rps3 and nad2) as well as four new mitochondrial genes (ribosomal small subunit protein genes: rps- 2, 7, 8, 10), previously undetected in ciliates due to their extreme divergence. The increased size of the Oxytricha mitochondrial genome relative to other ciliates is primarily a consequence of terminal expansions, rather than the retention of ancestral mitochondrial genes. Successive segmental duplications, visible in one of the two Oxytricha mitochondrial subterminal regions, appear to have contributed to the genome expansion. Consistent with pseudogene formation and decay, the subtermini possess shorter, more loosely packed open reading frames than the remainder of the genome. The mitochondrial plasmid shares a 251-bp region with 82% identity to the mitochondrial chromosome, suggesting that it most likely integrated into the chromosome at least once. This region on the chromosome is also close to the end of the most terminal member of a series of duplications, hinting at a possible association between the plasmid and the duplications. The presence of mitochondrial telomeres on the mitochondrial plasmid suggests that such plasmids may be a vehicle for lateral transfer of telomeric sequences between mitochondrial genomes. We conjecture that the extreme divergence observed in ciliate mitochondrial genomes may be due, in part, to repeated invasions by relatively error-prone DNA polymerase-bearing mobile elements.

The hydrogenosomes of Psalteriomonas lanterna

Background

Hydrogenosomes are organelles that produce molecular hydrogen and ATP. The broad phylogenetic distribution of their hosts suggests that the hydrogenosomes of these organisms evolved several times independently from the mitochondria of aerobic progenitors. Morphology and 18S rRNA phylogeny suggest that the microaerophilic amoeboflagellate Psalteriomonas lanterna, which possesses hydrogenosomes and elusive "modified mitochondria", belongs to the Heterolobosea, a taxon that consists predominantly of aerobic, mitochondriate organisms. This taxon is rather unrelated to taxa with hitherto studied hydrogenosomes.

Results

Electron microscopy of P. lanterna flagellates reveals a large globule in the centre of the cell that is build up from stacks of some 20 individual hydrogenosomes. The individual hydrogenosomes are surrounded by a double membrane that encloses a homogeneous, dark staining matrix lacking cristae. The "modified mitochondria" are found in the cytoplasm of the cell and are surrounded by 1-2 cisterns of rough endoplasmatic reticulum, just as the mitochondria of certain related aerobic Heterolobosea. The ultrastructure of the "modified mitochondria" and hydrogenosomes is very similar, and they have the same size distribution as the hydrogenosomes that form the central stack.

The phylogenetic analysis of selected EST sequences (Hsp60, Propionyl-CoA carboxylase) supports the phylogenetic position of P. lanterna close to aerobic Heterolobosea (Naegleria gruberi). Moreover, this analysis also confirms the identity of several mitochondrial or hydrogenosomal key-genes encoding proteins such as a Hsp60, a pyruvate:ferredoxin oxidoreductase, a putative ADP/ATP carrier, a mitochondrial complex I subunit (51 KDa), and a [FeFe] hydrogenase.

Conclusion

Comparison of the ultrastructure of the "modified mitochondria" and hydrogenosomes strongly suggests that both organelles are just two morphs of the same organelle. The EST studies suggest that the hydrogenosomes of P. lanterna are physiologically similar to the hydrogenosomes of Trichomonas vaginalis and Trimastix pyriformis. Phylogenetic analysis of the ESTs confirms the relationship of P. lanterna with its aerobic relative, the heterolobosean amoeboflagellate Naegleria gruberi, corroborating the evolution of hydrogenosomes from a common, mitochondriate ancestor.

RNA-mediated epigenetic programming of a genome-rearrangement pathway

Genome-wide DNA rearrangements occur in many eukaryotes but are most exaggerated in ciliates, making them ideal model systems for epigenetic phenomena. During development of the somatic macronucleus, Oxytricha trifallax destroys 95% of its germ line, severely fragmenting its chromosomes, and then unscrambles hundreds of thousands of remaining fragments by permutation or inversion. Here we demonstrate that DNA or RNA templates can orchestrate these genome rearrangements in Oxytricha, supporting an epigenetic model for sequence-dependent comparison between germline and somatic genomes. A complete RNA cache of the maternal somatic genome may be available at a specific stage during development to provide a template for correct and precise DNA rearrangement. We show the existence of maternal RNA templates that could guide DNA assembly, and that disruption of specific RNA molecules disables rearrangement of the corresponding gene. Injection of artificial templates reprogrammes the DNA rearrangement pathway, suggesting that RNA molecules guide genome rearrangement.

Ultrastructure and viability of isolated bovine preantral follicles

Techniques for the isolation of ovarian follicles and maturation of oocytes in vitro have enormous reproductive potential. Preservation of normal tissue function is vital. This study emphasizes the ultrastructure and viability of mechanically isolated bovine small (diameter 40-100 microm) preantral and large (140-450 microm) preantral/early antral follicles. Viability studies were performed for small preantral follicles. The presence of esterase activity, active mitochondria and dead cells served as parameters of oocyte and granulosa cell viability. After 1 day of culture, all follicles had a viable granulosa, displaying active mitochondria and/or esterase activity in all their cells, although a few (generally <5) dead granulosa cells were present in 17% of the follicles. Of the oocytes, 35 and 80% had esterase activity and active mitochondria respectively, whereas 8% appeared dead. The percentages of oocytes showing esterase activity and active mitochondria decreased during culture, whereas the percentage of follicles with dead oocytes or dead granulosa cells strongly increased. More than 90% of the isolated small follicles showed a poor ultrastructure, especially of their oocyte, which points to a negative selective isolation of poor follicles in the present study and/or an isolation procedure-induced damage of follicles. With respect to large preantral follicles, 42% of those distributed in the cortex and 64% of those isolated and cultured for 1 day had a poor ultrastructure. In contrast with the small ones, the percentage of ultrastructurally poor large preantral follicles had decreased to 27% after 5 days of culture, possibly due to better isolation and culture conditions. It is recommended to use ultrastructural and/or viability cell markers for in-vitro grown follicles to evaluate their quality, and particularly that of their oocytes.

Effects of conditioned media from murine granulosa cell lines on the growth of isolated bovine preantral follicles

Isolated morphologically normal bovine preantral follicles (40 to 70 microm) were cultured for 8 d in collagen gel in control medium or in 1 of 3 conditioned media from the murine granulosa cell lines GRMO1L, GRMO2 and GE2. The percentages of follicles at Day 1 that remained nomal at Day 8 were similar for follicles cultured in the conditioned and control media (84 to 90%). A significantly higher percentage of follicles cultured in each of 3 conditioned media started to grow (89%; P < 0.05) and their increase in diameter was greater than that of follicles cultured in control medium (72%; P < 0.05). The mitotic activity of the granulosa cells from follicles cultured in conditioned media was increased (P < 0.05) indicated by a higher percentage of nuclei that incorporated BrdU compared with that of follicles cultured in control medium. Follicular viability was measured by the presence of nonspecific esterase activity, active mitochondria and dead cells in cultured follicles using the fluorescent probes calcein-AM, rhodamine 123 and ethidium homodimer-1 in combination with confocal laser scanning microscopy. The percentages of follicles with esterase activity and active mitochondria present in their granulosa were similar for follicles in all groups. Culturing in GRMO2 or GE2 tended to lower the number of granulosa with dead cells. The percentage of follicles with oocytes without esterase activity and active mitochondria was lower (P < 0.05) in follicles cultured in GRMO2 or GE2 compared with those cultured in control medium. Moreover, the percentages of dead oocytes tended to be higher in follicles cultured in GRMO1L and GE2 compared with oocytes of follicles incubated in control medium. Taken together, the conditioned media stimulated follicular growth and granulosa viability as well as enhance mitotic activity of the granulosa cells. However, they negatively affected oocyte viability.

Gradual inhibition of inducible nitric oxide synthase but not of interleukin-1 beta production in rat microglial cells of endotoxin-treated mixed glial cell cultures

In cultures of purified microglial cells and astrocytes from newborn rats, the immunocytochemical localization of interleukin-1 beta (IL-1 beta) and inducible nitric oxide synthase (iNOS) using recently developed antibodies, as well as the release of IL-1 beta and nitric oxide (NO), was studied following exposure of the cells to endotoxin [lipopolysaccharide (LPS)]. In the absence of LPS, IL-1 beta- and iNOS-immunoreactive microglial cells and IL-1 beta or NO release were not observed, whereas in the presence of the endotoxin, the production of NO and IL-1 beta by microglial cells dramatically exceeded their synthesis and release by astrocytes. Interestingly, microglial cells cultured for 4-8 days in the presence of astrocytes appeared to lose their ability to produce iNOS, whereas the release of IL-1 beta remained unaltered. Moreover, endotoxin-stimulated microglial cells appeared to regain their ability to synthesize iNOS following their separation from astrocytes. These data show that microglia are primarily responsible for NO and IL-1 beta production in mixed glial cell cultures upon endotoxin stimulation. Moreover, in the presence of astrocytes the induction of iNOS, but not that of IL-1 beta in microglial cells is gradually inhibited.

Circulating tumor necrosis factor-alpha does not mediate endotoxin-induced hypothermia in rats

The present study was designed to investigate the role of macrophages and circulating tumor necrosis factor-alpha (TNF-alpha) in the endotoxin-induced hypothermic responses in rats. Intravenous as well as intraperitoneal administration of endotoxin to male Wistar rats (0.5 mg/kg) led to increased plasma TNF-alpha concentrations and a transient hypothermia, which reached its nadir after 90 min. The hypothermia and plasma TNF-alpha responses to endotoxin were abolished after elimination of peripheral macrophages. Seven days after the first challenge, tolerance of the hypothermic response was found if the same dose was administered intraperitoneally but not if it was administered intravenously. Tolerance of the TNF-alpha response was induced irrespective of the route of endotoxin administration. We hypothesize that, after intravenous administration of endotoxin, macrophage-dependent and -independent mechanisms are activated, whereas the hypothermic response to intraperitoneal endotoxin involves primarily macrophage-dependent mechanisms. These mechanisms may relate to the prime targets reached by endotoxin, such as macrophages and endothelial cells. Because the development of tolerance of the hypothermic response is dependent on the route of endotoxin administration, whereas that of the plasma TNF-alpha response is not, we conclude that circulating TNF-alpha is not the macrophage-derived cryogenic signal that triggers the hypothermic response.

Effects of monoclonal antibodies to specific epitopes of rat interleukin-1 beta (IL-1 beta) on IL-1 beta-induced ACTH, corticosterone and IL-6 responses in rats

Recently, we developed a panel of monoclonal antibodies (MoAbs) to rat IL-1 beta and found that MoAbs binding to the aminoacid sequences 66-85 and 123-143 of mature rIL-1 beta inhibited the binding of rIL-1 beta to murine EL4 cells. Here we study whether MoAbs to these and other domains of IL-1 interfere with the biological effects of rIL-1 beta in adult male rats in vivo. Administration of rIL-1 beta (1 or 5 micrograms/kg i.v.) enhanced the plasma concentrations of ACTH, corticosterone (CORT) and of IL-6 in a time- (0.5-4 h) and dose-dependent manner. Because 2 h after 5 micrograms/kg i.v., all three parameters were consistently elevated, this dose and time interval was used for further studies. Prior to injection, rIL-1 beta was incubated alone or in the presence of a MoAb (10 mg/kg) for 30 min at 37 degrees C or at 4 degrees C. Plasma ACTH, CORT and IL-6 responses to these mixtures are compared to those obtained after preincubation of rIL-1 beta with a non-IL-1 binding MoAb (PEN7). SILK 3, a MoAb that binds to the 66-85 domain of rIL-1 beta, reduced the ACTH and IL-6 responses by 48 and 45% respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Domains of rat interleukin 1 beta involved in type I receptor binding

In the present study the inhibitory effects of a panel of 21 monoclonal antibodies (moabs) to rat interleukin 1 beta (rIL-1 beta) on the binding of 125I-labeled rIL-1 beta to murine type I IL-1 receptors on EL4 cells were investigated. Furthermore, the epitopes of these moabs were determined by the use of the pepscan technique, and these epitopes were visualized on a three-dimensional model of rIL-1 beta. Some moabs (SILK 3, 4, 5, 6, and 22) inhibited receptor binding of radioiodinated rIL-1 beta at concentrations that are similar to the dissociation constant values of antibody-rIL-1 beta binding. Another group of moabs (SILK 7, 11, 20, 21, and 23) also inhibited receptor binding but only at concentrations that are 10-150 times higher than their dissociation constants. A large group of moabs did not affect receptor binding in the concentration range tested, and two moabs enhanced the binding of rIL-1 beta to type I receptors. The result of pepscan analysis shows that the moabs bound to one or more of the amino acid sequences 35-49, 66-85, 78-97, 106-124, and 123-143 of mature rIL-1 beta. Modeling of rIL-1 beta shows that the binding domains of SILK 4, 5, 6, and 22 (sequence 123-143) is located at the closed end of the molecule, indicating that this part of rIL-1 beta harbors domains that are crucial for type I receptor binding. The binding domain of SILK 3 (sequence 66-85) is also located at this end of the molecule. In contrast, the binding domains of SILK 7, 11, 20, 21, and 23 (sequence 78-97) are located at the open end of the molecule, which is at the same face as the amino- and carboxy-terminals. The binding domain of SILK 16 (sequence 106-124) is positioned at the center of the molecule. It is concluded that the closed end of rIL-1 beta contains sequences that are crucial for its binding to type I receptors on murine EL4 cells. Because of the high concentrations of antibodies to residues 78-97 of rIL-1 beta that are needed to interfere with receptor binding, the importance of these domains in binding to type I receptors remains uncertain.

ACTH response to a low dose but not a high dose of bacterial endotoxin in rats is completely mediated by corticotropin-releasing hormone

In experimental animals and humans, bacterial endotoxin activates the hypothalamus-pituitary-adrenal (HPA) axis. The pathways by which endotoxin stimulates adrenocorticotropic hormone (ACTH) and corticosterone secretion are uncertain. In the present study we compared the role of hypothalamic corticotropin-releasing hormone (CRH) in the activation of the HPA axis by a low (2.5 micrograms/kg) and a high (2.5 mg/kg) dose of bacterial endotoxin. Two experimental models were applied using chronically cannulated male Wistar rats. In the first model, rats were subjected to lesions of the hypothalamus that interrupted dorsal, lateral and frontal input to the median eminence (anterolateral deafferentation) or to sham operation and rats were used 7 days later. Before and at hourly intervals after endotoxin (2.5 micrograms/kg i.p.), blood samples were taken for the determination of plasma ACTH and corticosterone concentrations. Deafferentation of the hypothalamus strongly attenuated the elevations in plasma ACTH and corticosterone concentrations by a low dose of endotoxin compared to the responses in sham-operated animals. The second model involved passive immunization to CRH using a monoclonal antibody to rat/human CRH (PFU83). PFU83 (90 nmol/rat) abolished the elevation of plasma ACTH concentrations and attenuated corticosterone responses to a low dose of endotoxin (2.5 micrograms/kg i.p.) compared to that in control IgG-treated rats. Since the corticosterone responses to endotoxin were less effectively inhibited by the antibody than the ACTH responses, we postulate that non-ACTH-dependent mechanisms may contribute to the corticosterone response to endotoxin.(ABSTRACT TRUNCATED AT 250 WORDS)

Activation of the hypothalamus-pituitary-adrenal axis by bacterial endotoxins: routes and intermediate signals

Peripheral administration of endotoxin induces brain-mediated responses, including activation of the hypothalamus-pituitary-adrenal (HPA) axis and changes in thermoregulation. This paper reviews the mechanisms by which endotoxin affects these responses. The effects on thermoregulation are complex and include macrophage-dependent hyperthermic and hypothermic responses. Low doses of endotoxin, given IP, activate peripheral macrophages to produce interleukin (IL)-1 beta, which enters the circulation and acts as a hormonal signal. IL-1 may pass fenestrated endothelium in the median eminence to stimulate corticotropin-releasing hormone (CRH) secretion from the CRH nerve-terminals. In addition, IL-1 may activate brain endothelial cells to produce IL-1, IL-6, prostaglandins, etc., and secrete these substances into the brain. By paracrine actions, these substances may affect neurons (e.g., CRH neurons) or act on microglial cells, which show IL-1-induced IL-1 production and therefore amplify and prolong the intracerebral IL-1 signal. In contrast, high doses of endotoxin given i.v. may directly stimulate endothelial cells to produce IL-1, IL-6, and prostaglandin-E2 (PGE2) and thereby activate the HPA axis in a macrophage-independent manner.

Human recombinant interleukin-1 receptor antagonist prevents adrenocorticotropin, but not interleukin-6 responses to bacterial endotoxin in rats

The present study was designed to analyze the role of endogenous interleukin-1 (IL-1) in the ACTH, corticosterone (CORT), and IL-6 responses of rats to bacterial endotoxin. Recombinant rat IL-1 beta (rIL-1 beta) when given ip resulted in dose-dependent increases in plasma ACTH, CORT, and IL-6 concentrations. Plasma ACTH and CORT responses could be induced by low rIL-1 beta doses that did not elevate plasma IL-6 levels. The half-maximally effective dose of rIL-1 beta was less than 0.6 microgram/kg for the ACTH and CORT responses and higher than 2.5 micrograms/kg for the IL-6 response. Time-course studies indicated that plasma ACTH and CORT concentrations were already elevated 30 min after the injection of rIL-1 beta (2.5 micrograms/kg, ip), with peak values after 1-2 h, followed by a subsequent decline. In contrast, plasma IL-6 concentrations became elevated 2 h after the injection of rIL-1 beta. In another set of experiments, the administration of endotoxin resulted in a dose-dependent elevation of the plasma ACTH, CORT, and IL-6 concentrations. The dose-response characteristics for ACTH, CORT, and IL-6 were different. The half-maximally effective dose for the ACTH and CORT, and IL-6 responses were approximately 2.5 micrograms/kg and more than 10 micrograms/kg, respectively. Time courses of plasma ACTH, CORT, and IL-6 responses to endotoxin (2.5 micrograms/kg, ip) were similar, with peak values measured after 2 h. When given alone, the human IL-1 receptor antagonist (IL-1RA; 1 or 2.5 mg/kg, ip) did not affect resting plasma ACTH and CORT concentrations and reduced plasma IL-6 concentrations in one experiment. At a dose of 1 mg/kg, IL-1RA inhibited ACTH and IL-6 responses to rIL-1 beta (2.5 micrograms/kg, ip) by 75% and 90%, respectively. Administration of IL-1RA (2.5 mg/kg, ip) 30 min after endotoxin (2.5 micrograms/kg, ip) completely prevented the ACTH response and partially inhibited the CORT response, but did not affect the IL-6 response measured 2.5 h after endotoxin administration. We conclude that 1) IL-1 receptors are involved in the ACTH and IL-6 responses to rat IL-1 beta; 2) the ACTH response, but not the IL-6 response, to a low dose dose of endotoxin in rats requires IL-1 receptor activation by endogenous produced IL-1; and 3) circulating IL-6 is not a prime mediator involved in ACTH and CORT responses to low doses of rIL-1 beta and endotoxin.

Nonionic block polymer surfactants modulate the humoral immune response against Streptococcus pneumoniae-derived hexasaccharide-protein conjugates

Nonionic block polymer surfactants (NBPs) were tested for the capacity to stimulate the antibody response against hexasaccharide (HS), derived from Streptococcus pneumoniae type 3 capsular polysaccharide (S3PS), which was conjugated to proteins. The immune response was evaluated in the (CBA/N x BALB/c)F1 progeny, in which female mice are phenotypically normal whereas male mice carry an X-chromosome-linked immunodeficiency. NBPs L101, L121, 1101, and 1501 were able to increase anti-HS immunoglobulin M (IgM) and IgG levels in both normal and X-chromosome-linked immunodeficient mice (with up to 74-fold stimulation of antibody titers). Distribution of S3PS-specific antibodies over the various IgG isotypes was restricted after immunization with either HS-bovine serum albumin or HS-keyhole limpet hemocyanin (HS-KLH). Addition of NBPs (in particular 1501) resulted in a more diverse immune response with either antigen as judged by isotype distribution. Isoelectric focusing of individual sera and subsequent detection of S3PS-binding antibodies in these sera by immunochemical staining revealed a restricted number of different spectrotypes in the course of the immune response. Upon immunization of mice with HS-KLH, spectra of secreted antibodies were slightly more complex and more densely stained than after immunization with HS-bovine serum albumin. Furthermore, NBPs 1101 and 1501 appeared to be able to stimulate the secretion of antibodies, which were secreted only in small amounts without the use of NBPs. Different explanations for increased spectrotype diversity after immunization with KLH as the carrier and after administration of NBPs as the adjuvant are discussed.