Homozygous C1q deficiency causes glomerulonephritis associated with multiple apoptotic bodies

The complement system plays a paradoxical role in the development and expression of autoimmunity in humans. The activation of complement in systemic lupus erythematosus (SLE) contributes to tissue injury. In contrast, inherited deficiency of classical pathway components, particularly C1q (ref. 1), is powerfully associated with the development of SLE. This leads to the hypothesis that a physiological action of the early part of the classical pathway protects against the development of SLE (ref. 2) and implies that C1q may play a key role in this respect. C1q-deficient (C1qa-/-) mice were generated by gene targeting and monitored for eight months. C1qa-/- mice had increased mortality and higher titres of autoantibodies, compared with strain-matched controls. Of the C1qa-/- mice, 25% had glomerulonephritis with immune deposits and multiple apoptotic cell bodies. Among mice without glomerulonephritis, there were significantly greater numbers of glomerular apoptotic bodies in C1q-deficient mice compared with controls. The phenotype associated with C1q deficiency was modified by background genes. These findings are compatible with the hypothesis that C1q deficiency causes autoimmunity by impairment of the clearance of apoptotic cells.

Differential H4 acetylation of paternal and maternal chromatin precedes DNA replication and differential transcriptional activity in pronuclei of 1-cell mouse embryos

In the mouse embryo, transcriptional activation begins during S/G2 phase of the first cell cycle when paternal and maternal chromatin are still in separate nuclear entities within the same cytoplasm. At this time, the male pronucleus exhibits greater transcriptional activity than the female pronucleus. Since acetylation of histones in the nucleosome octamer exerts a regulatory influence on gene expression, we investigated changes in histone acetylation during the remodeling of paternal and maternal chromatin from sperm entry through to minor genome activation and mitosis. We found (1) neither mature sperm nor metaphase II maternal chromatin stained for hyperacetylated histone H4; (2) immediately following fertilization, hyperacetylated H4 was associated with paternal but not maternal chromatin while, in parthenogenetically activated oocytes, maternal chromatin became hyperacetylated; (3) in zygotes, differential levels and patterns of hyperacetylated H4 between male and female pronuclei persisted throughout most of G1 with histone deacetylases and acetyltransferases already active at this time; (4) when transcriptional differences are observed in S/G2, male and female pronuclei have equivalent levels of H4 hyperacetylation and DNA replication was not required to attain this equivalence and (5) in contrast to the lack of H4 hyperacetylation on gametic chromatin, chromosomes at the first mitosis showed distinct banding patterns of H4 hyperacetylation. These results suggest that sperm chromatin initially out-competes maternal chromatin for the pool of hyperacetylated H4 in the oocyte, that hyperacetylated H4 participates in the process of histone-protamine exchange in the zygote, and that differences in H4 acetylation in male and female pronuclei during G1 are translated across DNA replication to transcriptional differences in S/G2. Prior to fertilization, neither paternal nor maternal chromatin show memory of H4 hyperacetylation patterns but, by the end of the first cell cycle, before major zygotic genome activation at the 2-cell stage, chromosomes already show hyperacetylated H4 banding patterns.

Childhood cerebellar tumours mirror conserved fetal transcriptional programs

Study of the origin and development of cerebellar tumours has been hampered by the complexity and heterogeneity of cerebellar cells that change over the course of development. Here we use single-cell transcriptomics to study more than 60,000 cells from the developing mouse cerebellum and show that different molecular subgroups of childhood cerebellar tumours mirror the transcription of cells from distinct, temporally restricted cerebellar lineages. The Sonic Hedgehog medulloblastoma subgroup transcriptionally mirrors the granule cell hierarchy as expected, while group 3 medulloblastoma resembles Nestin+ stem cells, group 4 medulloblastoma resembles unipolar brush cells, and PFA/PFB ependymoma and cerebellar pilocytic astrocytoma resemble the prenatal gliogenic progenitor cells. Furthermore, single-cell transcriptomics of human childhood cerebellar tumours demonstrates that many bulk tumours contain a mixed population of cells with divergent differentiation. Our data highlight cerebellar tumours as a disorder of early brain development and provide a proximate explanation for the peak incidence of cerebellar tumours in early childhood.

Characterization of the 18S rRNA gene for designing universal eukaryote specific primers

High throughput sequencing technology has great promise for biodiversity studies. However, an underlying assumption is that the primers used in these studies are universal for the prokaryotic or eukaryotic groups of interest. Full primer universality is difficult or impossible to achieve and studies using different primer sets make biodiversity comparisons problematic. The aim of this study was to design and optimize universal eukaryotic primers that could be used as a standard in future biodiversity studies. Using the alignment of all eukaryotic sequences from the publicly available SILVA database, we generated a full characterization of variable versus conserved regions in the 18S rRNA gene. All variable regions within this gene were analyzed and our results suggested that the V2, V4 and V9 regions were best suited for biodiversity assessments. Previously published universal eukaryotic primers as well as a number of self-designed primers were mapped to the alignment. Primer selection will depend on sequencing technology used, and this study focused on the 454 pyrosequencing GS FLX Titanium platform. The results generated a primer pair yielding theoretical matches to 80% of the eukaryotic and 0% of the prokaryotic sequences in the SILVA database. An empirical test of marine sediments using the AmpliconNoise pipeline for analysis of the high throughput sequencing data yielded amplification of sequences for 71% of all eukaryotic phyla with no isolation of prokaryotic sequences. To our knowledge this is the first characterization of the complete 18S rRNA gene using all eukaryotes present in the SILVA database, providing a robust test for universal eukaryotic primers. Since both in silico and empirical tests using high throughput sequencing retained high inclusion of eukaryotic phyla and exclusion of prokaryotes, we conclude that these primers are well suited for assessing eukaryote diversity, and can be used as a standard in biodiversity studies.

Prognostic value of medulloblastoma extent of resection after accounting for molecular subgroup: a retrospective integrated clinical and molecular analysis

Background

Incomplete surgical resection of medulloblastoma is controversially considered a marker of high-risk disease; driving aggressive surgical resections, “second-look” surgeries, and/or intensified chemoradiotherapy. All prior publications evaluating the clinical importance of extent of resection (EOR) failed to account for molecular subgroup. We analysed the prognostic value of EOR across 787 medulloblastoma samples in a subgroup-specific manner.

Methods

We retrospectively identified patients from Medulloblastoma Advanced Genomics International Consortium (MAGIC) centres with a histological diagnosis of medulloblastoma and complete extent of resection and survival data. Specimens were collected from 35 international institutions. Medulloblastoma subgroup affiliation was determined using nanoString gene expression profiling on frozen or formalin-fixed paraffin-embedded tissues. Extent of resection (EOR) based on post-operative imaging was classified as gross total (GTR), near total (NTR, <1·5cm²), or subtotal (STR, ≥ 1·5cm²). Overall survival (OS) and progression-free survival (PFS) multivariable analyses including subgroup, age, metastatic status, geographical location of therapy (North America/Australia vs world), and adjuvant therapy regimen were performed. The primary endpoint was the impact of surgical EOR by molecular subgroup and other clinical variables on OS and PFS.

Findings

787 medulloblastoma patients (86 WNT, 242 SHH, 163 Group 3, and 296 Group 4) were included in a multivariable Cox model of PFS and OS. The marked benefit of EOR in the overall cohort was greatly attenuated after including molecular subgroup in the multivariable analysis. There was an observed PFS benefit of GTR over STR (hazard ration [HR] 1·45, 95% CI; 1·07–1·96, p=0·02) but there was no observed PFS or OS benefit of GTR over NTR (HR 1·05, 0·71–1·53, p=0·82 and HR 1·14, 0·75–1·72, p=0.55). There was no statistically significant survival benefit to greater EOR for patients with WNT, SHH, or Group 3 patients (HR 1·03, 0·67–1·58, p=0·9 for STR vs. GTR). There was a PFS benefit for GTR over STR in patients with Group 4 medulloblastoma (HR1·97, 1·22–3·17, p=0·01), particularly those with metastatic disease (HR 2·22, 1–4·93, p=0·05). A nomogram based on this multivariable cox proportional hazards model shows the comparably smaller impact of EOR on relative risk for PFS and OS than subgroup affiliation, metastatic status, radiation dose, and adjuvant chemotherapy.

Interpretation

The prognostic benefit of EOR for patients with medulloblastoma is attenuated after accounting for molecular subgroup affiliation. Although maximal safe surgical resection should remain the standard of care, surgical removal of small residual portions of medulloblastoma is not recommended when the likelihood of neurological morbidity is high as there is no definitive benefit to GTR over NTR. Our results suggest a re-evaluation of the long-term implications of intensified craniospinal irradiation (36 Gy) in children with small residual portions of medulloblastoma.

Funding

Funding Canadian Cancer Society Research Institute, Terry Fox Research Institute, Canadian Institutes of Health Research, National Institutes of Health, Pediatric Brain Tumor Foundation, Garron Family Chair in Childhood Cancer Research.

Plasticity of animal genome architecture unmasked by rapid evolution of a pelagic tunicate

Genomes of animals as different as sponges and humans show conservation of global architecture. Here we show that multiple genomic features including transposon diversity, developmental gene repertoire, physical gene order, and intron-exon organization are shattered in the tunicate Oikopleura, belonging to the sister group of vertebrates and retaining chordate morphology. Ancestral architecture of animal genomes can be deeply modified and may therefore be largely nonadaptive. This rapidly evolving animal lineage thus offers unique perspectives on the level of genome plasticity. It also illuminates issues as fundamental as the mechanisms of intron gain.

Expression of the HSP 70.1 gene, a landmark of early zygotic activity in the mouse embryo, is restricted to the first burst of transcription

Activation of the mouse embryonic genome at the 2-cell stage is characterized by the synthesis of several alpha-amanitin-sensitive polypeptides, some of which belong to the multigenic hsp 70 family. In the present work we show that a member of this family, the HSP 70.1 gene, is highly transcribed at the onset of zygotic genome activation. Transcription of this gene began as early as the 1-cell stage. Expression of the gene continued through the early 2-cell stage but was repressed before the completion of the second round of DNA replication. During this period we observed that the level of transcription was modulated by in vitro culture conditions. The coincidence of repression of HSP70.1 transcription with the second round of DNA replication was not found for other transcription-dependent polypeptides synthesized at the 2-cell stage.

Identification of the gene (SEDL) causing X-linked spondyloepiphyseal dysplasia tarda

Spondyloepiphyseal dysplasia tarda (SEDL; MIM 313400) is an X-linked recessive osteochondrodysplasia that occurs in approximately two of every one million people. This progressive skeletal disorder which manifests in childhood is characterized by disproportionate short stature with short neck and trunk, barrel chest and absence of systemic complications. Distinctive radiological signs are platyspondyly with hump-shaped central and posterior portions, narrow disc spaces, and mild to moderate epiphyseal dysplasia. The latter usually leads to premature secondary osteoarthritis often requiring hip arthroplasty. Obligate female carriers are generally clinically and radiographically indistinguishable from the general population, although some cases have phenotypic changes consistent with expression of the gene defect. The SEDL gene has been localized to Xp22 (refs 8,9) in the approximately 2-Mb interval between DXS16 and DXS987 (ref. 10). Here we confirm and refine this localization to an interval of less than 170 kb by critical recombination events at DXS16 and AFMa124wc1 in two families. In one candidate gene we detected three dinucleotide deletions in three Australian families which effect frameshifts causing premature stop codons. The gene designated SEDL is transcribed as a 2.8-kb transcript in many tissues including fetal cartilage. SEDL encodes a 140 amino acid protein with a putative role in endoplasmic reticulum (ER)-to-Golgi vesicular transport.

Fc gamma RIIa polymorphism in systemic lupus erythematosus (SLE): no association with disease

An allotypic variant of Fc gamma RIIa, Fc gamma RIIa-HR (Fc gamma RIIa-R131), has been shown in vitro to reduce the capacity of phagocytic cells to bind and internalize IgG-containing immune complexes. Our aim was to determine whether this allotypic variant was associated with susceptibility to SLE and the development of lupus nephritis, as previous studies have suggested. Fc gamma RIIA genotype analysis was performed by amplification refractory mutation system-polymerase chain reaction (ARMS-PCR) in 215 Caucasoid, 70 Afro-Caribbean, and 46 Chinese patients with SLE, and in 259,77 and 49 ethnically matched controls, respectively. Distribution of Fc gamma RIIa genotypes between the patients and ethnically matched controls was not significantly different in the three populations studied. No association between the Fc gamma RIIa-HR allotype and nephritis was found. Our results suggest that the Fc gamma RIIa-HR allotype is not a major factor predisposing to the development of SLE, or to lupus nephritis.

The origins of marine bioluminescence: turning oxygen defence mechanisms into deep-sea communication tools

Bioluminescence, the emission of ecologically functional light by living organisms, emerged independently on several occasions, yet the evolutionary origins of most bioluminescent systems remain obscure. We propose that the luminescent substrates of the luminous reactions (luciferins) are the evolutionary core of most systems, while luciferases, the enzymes catalysing the photogenic oxidation of the luciferin, serve to optimise the expression of the endogenous chemiluminescent properties of the luciferin. Coelenterazine, a luciferin occurring in many marine bioluminescent groups, has strong antioxidative properties as it is highly reactive with reactive oxygen species such as the superoxide anion or peroxides. We suggest that the primary function of coelenterazine was originally the detoxification of the deleterious oxygen derivatives. The functional shift from its antioxidative to its light-emitting function might have occurred when the strength of selection for antioxidative defence mechanisms decreased. This might have been made possible when marine organisms began colonising deeper layers of the oceans, where exposure to oxidative stress is considerably reduced because of reduced light irradiance and lower oxygen levels. A reduction in metabolic activity with increasing depth would also have decreased the endogenous production of reactive oxygen species. Therefore, in these organisms, mechanisms for harnessing the chemiluminescence of coelenterazine in specialised organs could have developed, while the beneficial antioxidative properties were maintained in other tissues. The full range of graded irradiance in the mesopelagic zone, where the majority of organisms are bioluminescent, would have provided a continuum for the selection and improvement of proto-bioluminescence. Although the requirement for oxygen or reactive oxygen species observed in bioluminescent systems reflects the high energy required to produce visible light, it may suggest that oxygen-detoxifying mechanisms provided excellent foundations for the emergence of many bioluminescent systems.

Cloning and expression of cDNA for the luciferase from the marine ostracod Vargula hilgendorfii

The marine ostracod Vargula hilgendorfii ejects luciferin and luciferase into seawater to produce a bright luminous cloud. The light is due to the oxidation of luciferin, an imidazopyrazine compound, by molecular oxygen, catalyzed by luciferase. The mechanism of the reaction has been studied extensively and the 60 kcal/mol required for the blue emission have been shown to be derived from the oxidation of luciferin via a dioxetanone intermediate, in which the excited state oxyluciferin bound to luciferase is the emitter. However, only limited information is available regarding the properties of the enzyme. This paper reports the cloning and sequence analysis of the cDNA for Vargula luciferase and the expression of the cDNA in a mammalian cell system. The primary structure, deduced from the nucleotide sequence, consists of 555 amino acid residues in a single polypeptide chain with a molecular weight of 62,171. Two regions of the enzyme show significant amino acid sequence homology with an N-terminal segment of the photoprotein aequorin. The Vargula luciferase gene, which contains a signal sequence for secretion, should be well suited as a reporter in studies of gene expression.

Spliced-leader RNA trans splicing in a chordate, Oikopleura dioica, with a compact genome

trans splicing of a spliced-leader RNA (SL RNA) to the 5' ends of mRNAs has been shown to have a limited and sporadic distribution among eukaryotes. Within metazoans, only nematodes are known to process polycistronic pre-mRNAs, produced from operon units of transcription, into mature monocistronic mRNAs via an SL RNA trans-splicing mechanism. Here we demonstrate that a chordate with a highly compact genome, Oikopleura dioica, now joins Caenorhabditis elegans in coupling trans splicing with processing of polycistronic transcipts. We identified a single SL RNA which associates with Sm proteins and has a trimethyl guanosine cap structure reminiscent of spliceosomal snRNPs. The same SL RNA, estimated to be trans-spliced to at least 25% of O. dioica mRNAs, is used for the processing of both isolated or first cistrons and downstream cistrons in a polycistronic precursor. Remarkably, intercistronic regions in O. dioica are far more reduced than those in either nematodes or kinetoplastids, implying minimal cis-regulatory elements for coupling of 3'-end formation and trans splicing.

Optimal timing of autologous cranioplasty after decompressive craniectomy in children

OBJECT

The object of this study was to determine if early cranioplasty after decompressive craniectomy for elevated intracranial pressure in children reduces complications.

METHODS

Sixty-one consecutive cases involving pediatric patients who underwent autologous cranioplasty after decompressive craniectomy for raised intracranial pressure at a single academic children's hospital over 15 years were studied retrospectively.

RESULTS

Sixty-one patients were divided into early (< 6 weeks; 28 patients) and late (≥ 6 weeks; 33 patients) cranioplasty cohorts. The cohorts were similar except for slightly lower age in the early (8.03 years) than the late (10.8 years) cranioplasty cohort (p < 0.05). Bone resorption after cranioplasty was significantly more common in the late (42%) than the early (14%) cranioplasty cohort (p < 0.05; OR 5.4). No other complication differed in incidence between the cohorts.

CONCLUSIONS

After decompressive craniectomy for raised intracranial pressure in children, early (< 6 weeks) cranioplasty reduces the occurrence of reoperation for bone resorption, without altering the incidence of other complications.

The paradoxical effect of bevacizumab in the therapy of malignant gliomas

One rationale behind the use of agents that inhibit vascular endothelial growth factor in the therapy of primary CNS malignancies is based upon the concept that normalization of tumor vasculature with a decrease in tumor interstitial pressure will improve access of cytoreductive drugs and improve radiotherapy efficacy due to increased oxygen delivery. However, several studies have raised the concern that these agents may both rapidly restore the low permeability characteristics of the blood-brain barrier and counteract the beneficial effect of pseudoprogression. The result may be decreased therapeutic efficacy while increasing infiltration by co-opting normal vessels. In this discussion, we examine both histologic and radiographic tumor progression in the context of antiangiogenic agents. Issues dealing with the safety of bevacizumab (Avastin®, Genentech, South San Francisco, CA) and its potential to decrease efficacy of standard radiochemotherapy when used to treat patients with newly diagnosed malignant glioma are emphasized.

Progressive maturation of chromatin structure regulates HSP70.1 gene expression in the preimplantation mouse embryo

In the widely studied model organisms, Drosophila and Xenopus, early embryogenesis involves an extended series of nuclear divisions prior to activation of the zygotic genome. The mammalian embryo differs in that the early cleavage phase is already characterized by regulated cell cycles with specific zygotic gene expression. In the mouse, where major activation of the zygotic genome occurs at the 2-cell stage, the HSP70.1 gene is among the earliest genes to be expressed. We investigated the developmentally regulated expression of this gene during the preimplantation period, using a luciferase transgene, with or without flanking scaffold attachment regions (SARs). Cleavage stage-specific modifications in expression profiles were examined in terms of histone H4 acetylation status, topoisomerase II activity, and the localisation of HMG-I/Y, a nuclear protein with known affinity for the AT-tracts of SARs. We demonstrate that HSP70.1-associated transcription factors are not limiting, and that instead, there is a progressive maturation of chromatin structure that is directly involved in HSP70.1 regulation during early mouse development.

Recurrence risks and prognosis in severe sporadic osteogenesis imperfecta

A study was carried out in the United Kingdom of patients with severe osteogenesis imperfecta (OI), born with fractures to normal parents, in order to determine recurrence risks. A total of 105 cases from 98 families survived the perinatal period and 60 cases from 57 families were stillborn or died during the first week of life. The majority of the perinatal survivors correspond to the overlapping group of Sillence type III and sporadic type IV OI. In 40 of these, the radiograph at birth was available and in 37 it showed a characteristic appearance similar to that described previously for type III OI. The other three cases had radiological type IIB OI at birth and died before 26 months of age. The patients with perinatally lethal OI were subdivided on radiological appearance into Sillence type IIA (30 cases, described in the previous paper), type IIB (12 cases from 11 families), and type IIC (three cases from three families), and in five cases from three families the radiological appearance was the same as that of the 37 perinatal survivors described above. Ten cases from 10 families were not classified because their radiographs were unavailable. To analyse the empirical recurrence risks, patients were grouped according to radiological appearance at birth. Those with a type III-like pattern numbered 42 cases and they were grouped with the other cases of severe deforming OI who survived the perinatal period, for whom no x ray at birth was available, making a total of 107 cases. Taking one affected child per family as the proband, there were 98 probands. They had 146 sibs, of whom 10 were affected, giving an empirical recurrence risk of 6.9%. This is consistent with the disease arising as a new dominant mutation in about three quarters of families and as a recessive in about one quarter in this heterogeneous group. It is reasonable to give a recurrence risk of up to 25% in cases with parental consanguinity and a risk of 4.4% in cases with unrelated parents. Fifteen patients (14 probands) with Sillence type IIB OI had 13 sibs, one affected, giving an empirical recurrence risk of 7.7%. The parents were consanguineous in three families and the evidence for autosomal recessive inheritance for the majority in this group is probably stronger. The three patients with type IIC OI had three healthy sibs and the 10 unclassifiable perinatally lethal cases had 22 sibs, all normal. The radiological appearance at birth predicts prognosis to some extent; essentially, the better the bone morphology and mineralisation the longer the survival.

Failure of human rhombic lip differentiation underlies medulloblastoma formation

Medulloblastoma (MB) comprises a group of heterogeneous paediatric embryonal neoplasms of the hindbrain with strong links to early development of the hindbrain1-4. Mutations that activate Sonic hedgehog signalling lead to Sonic hedgehog MB in the upper rhombic lip (RL) granule cell lineage5-8. By contrast, mutations that activate WNT signalling lead to WNT MB in the lower RL9,10. However, little is known about the more commonly occurring group 4 (G4) MB, which is thought to arise in the unipolar brush cell lineage3,4. Here we demonstrate that somatic mutations that cause G4 MB converge on the core binding factor alpha (CBFA) complex and mutually exclusive alterations that affect CBFA2T2, CBFA2T3, PRDM6, UTX and OTX2. CBFA2T2 is expressed early in the progenitor cells of the cerebellar RL subventricular zone in Homo sapiens, and G4 MB transcriptionally resembles these progenitors but are stalled in developmental time. Knockdown of OTX2 in model systems relieves this differentiation blockade, which allows MB cells to spontaneously proceed along normal developmental differentiation trajectories. The specific nature of the split human RL, which is destined to generate most of the neurons in the human brain, and its high level of susceptible EOMES+KI67+ unipolar brush cell progenitor cells probably predisposes our species to the development of G4 MB.

Real time imaging of transcriptional activity in live mouse preimplantation embryos using a secreted luciferase

Study of gene expression kinetics during preimplantation mammalian development is difficult because of the limited amount of material and the usually destructive, static nature of molecular analyses. We describe continuous, noninvasive monitoring of gene expression in preimplantation embryos by using a secreted luminescent reporter, Vargula luciferase. Transgene expression profiles were followed by assaying aliquots of culture medium or by direct visualization of Vargula luciferase secretion from living embryos in real time through photon imaging. With this approach, it is possible to observe epigenetic modulations of gene expression and to link this over time to the developmental capacity of individual embryos. In addition, by developing a strategy where expression from integrated transgenes is enhanced relative to that from nonintegrated DNA, we provide evidence that rapid detection of transgene integration prior to the blastocyst stage should be possible. Thus, imaging of Vargula luciferase secretion may also be useful in the early screening of embryos, for example, in the production of transgenic livestock.

Amniotic bands in connective tissue disorders

Amniotic bands are described in two children with Ehlers-Danlos syndrome type IV and in one with severe osteogenesis imperfecta. Since the basic defect in both of these disorders rests in collagen, which constitutes the main component of the load bearing amnion, it is proposed that these cases provide further insight into the pathogenesis of amniotic bands.

Identification of intervals on chromosomes 1, 3, and 13 linked to the development of lupus in BXSB mice

OBJECTIVE

To identify intervals containing systemic lupus erythematosus (SLE) susceptibility alleles in the BXSB strain of mice.

METHODS

We analyzed 286 (B10 x [B10 x BXSB]F1) backcross mice for a range of phenotypic traits associated with the development of SLE in BXSB mice. The mice were genotyped using 93 microsatellite markers, and the linkage of these markers to disease was studied by extreme-phenotype and quantitative trait locus analysis.

RESULTS

The disease phenotype in these backcross mice was less severe than that in BXSB mice. However, antinuclear antibody production was increased compared with the parental strain. We identified 4 areas of genetic linkage to disease on chromosome 1 (Bxs1-4), 1 on chromosome 3 (Bxs5), and another interval on chromosome 13 which were associated with various aspects of the phenotype. Bxs4 and Bxs5 are located in regions not previously linked to disease in other models of SLE.

CONCLUSION

SLE in the BXSB mouse model has a complex genetic basis and involves at least 5 distinct intervals located on chromosomes 1 and 3. There is evidence that different intervals affect particular aspects of the SLE phenotype.

Differential preimplantation regulation of two mouse homologues of the yeast SWI2 protein

Epigenetic regulation of gene expression through modification of chromatin organization is an important mechanism in the development of eucaryotic organisms. We investigated the developmentally regulated expression of the mouse mBRG1 and mbrm genes, which are homologous to the yeast SWI2 gene. Both proteins are involved in chromatin remodeling as components of the mammalian SWI/SNF complex. The analysis was performed at a time in mouse development when the formation of a functional zygotic nucleus is closely linked to extensive chromatin modifications. Reverse transcription-polymerase chain reaction (RT-PCR) analysis in mature oocytes and through the first cleavage stages showed that both genes were highly expressed as maternal products but that they subsequently exhibited considerable differences in their level of expression when the transition to zygotic transcription occurred. Immunodetection of the two proteins with specific antibodies paralleled the RT-PCR analysis. The mBRG1 protein was present throughout preimplantation development, whereas zygotic mbrm was clearly detectable only when differentiation first occurs at the blastocyst stage. At this stage, mbrm was restricted to the inner cell mass. Cell type-specific expression of mbrm was also observed after in vitro differentiation of embryonic stem cells. These results indicate that the two murine homologues of SWI2 have substantially different roles in chromatin organization during the onset of embryonic development.

Development of scarring and renal failure in a rat model of crescentic glomerulonephritis

BACKGROUND

The aim of this study was to develop and characterize a rat model of crescentic glomerulonephritis which progresses to glomerulosclerosis and renal failure.

METHODS

Glomerulonephritis was induced in Wistar Kyoto rats by a single injection of rabbit anti-glomerular basement membrane antiserum. Albuminuria and serum creatinine were monitored. Kidneys were examined, from 2.5 h to 44 days, using light-microscopy and immunohistochemistry. To characterize the glomerular inflammatory infiltrate, glomeruli were digested to single cells and analysed by fluorescence-activated cell sorter (FACS) and by immunohistochemistry on cytospins.

RESULTS

Rats developed albuminuria by 4 days and increased serum creatinine by day 18. Histology showed glomerular fibrinoid necrosis by day 4 and cellular crescents in a mean of 63% of glomeruli by day 11. By 6 weeks, rats had developed renal failure (mean creatinine >300 micromol/l) with 94% of the glomeruli showing glomerulosclerosis. The kidneys were also affected by severe interstitial nephritis and tubular loss. The glomeruli were infiltrated by monocytes/ macrophages (ED1+) and CD8+ (OX8+) cells. FACS analysis showed that CD8+ cells did not express T-cell markers (CD3, TCRalphabeta or TCRgammadelta) or the NK-cell marker (NKR-P1). FACS analysis of peripheral blood mononuclear cells demonstrated a population of monocytes reactive with OX8, and double-labelling of cytospin preparations of glomerular digests showed that a proportion of the CD8+ cells were a subset of ED1+ monocyte/macrophages.

CONCLUSIONS

We have characterized a reproducible model of crescentic glomerulonephritis which rapidly progresses to chronic renal failure with glomerulosclerosis and tubulo-interstitial scarring. This model will be useful for testing new therapeutic approaches in crescentic glomerulonephritis.

Mouse embryos do not wait for the MBT: chromatin and RNA polymerase remodeling in genome activation at the onset of development

In Xenopus and Drosophila embryos, activation of the zygotic genome occurs after a series of rapid nuclear divisions in which DNA replication occupies most of the cell cycle. In these organisms, it has been proposed that zygotic transcription does not begin until a threshold nucleocytoplasmic ratio has been obtained in which repressive factors are titrated out and interphase becomes long enough to allow synthesis of transcripts. In mammalian embryos, however, a model of threshold nucleocytoplasmic ratios does not seem to apply, as beginning with the 1-cell stage, there are regulated cell cycles with the expression of zygotic transcripts during the cleavage period. By taking advantage of the slower kinetics at the onset of mouse development, we have characterized changes in chromatin structure and the basal transcription machinery throughout the transition from transcriptional incompetence, to minor activation of the zygotic genome during the 1-cell stage, and through major genome activation at the 2-cell stage. Further maturation of chromatin structure continues through subsequent cleavage cycles as a foundation for the first cellular differentiations in the blastocyst. The epigenetic chromatin modifications that occur during the cleavage period may have long range and inheritable effects and are undoubtedly important in the ability of the mammalian oocyte to remodel previously defined nuclear structures and cell fates.