The longevity and reversibility of quiescence in Schizosaccharomyces pombe are dependent upon the HIRA histone chaperone

Quiescence (G0) is a reversible non-dividing state that facilitates cellular survival in adverse conditions. Here, we demonstrate that the HIRA histone chaperone complex is required for the reversibility and longevity of nitrogen starvation-induced quiescence in Schizosaccharomyces pombe. The HIRA protein, Hip1 is not required for entry into G0 or the induction of autophagy. Although hip1Δ cells retain metabolic activity in G0, they rapidly lose the ability to resume proliferation. After a short period in G0 (1 day), hip1Δ mutants can resume cell growth in response to the restoration of a nitrogen source but do not efficiently reenter the vegetative cell cycle. This correlates with a failure to induce the expression of MBF transcription factor-dependent genes that are critical for S phase. In addition, hip1Δ G0 cells rapidly progress to a senescent state in which they can no longer re-initiate growth following nitrogen source restoration. Analysis of a conditional hip1 allele is consistent with these findings and indicates that HIRA is required for efficient exit from quiescence and prevents an irreversible cell cycle arrest

The longevity and reversibility of quiescence in <em>Schizosaccharomyces pombe</em> are dependent upon the HIRA histone chaperone

Quiescence (G0) is a reversible non-dividing state that facilitates cellular survival in adverse conditions. Here, we demonstrate that the HIRA histone chaperone complex is required for the reversibility and longevity of nitrogen starvation-induced quiescence in Schizosaccharomyces pombe. The HIRA protein, Hip1 is not required for entry into G0 or the induction of autophagy. Although hip1Δ cells retain metabolic activity in G0, they rapidly lose the ability to resume proliferation. After a short period in G0 (1 day), hip1Δ mutants can resume cell growth in response to the restoration of a nitrogen source but do not efficiently reenter the vegetative cell cycle. This correlates with a failure to induce the expression of MBF transcription factor-dependent genes that are critical for S phase. In addition, hip1Δ G0 cells rapidly progress to a senescent state in which they can no longer re-initiate growth following nitrogen source restoration. Analysis of a conditional hip1 allele is consistent with these findings and indicates that HIRA is required for efficient exit from quiescence and prevents an irreversible cell cycle arrest

Abo1, a conserved bromodomain AAA-ATPase, maintains global nucleosome occupancy and organisation.

Maintenance of the correct level and organisation of nucleosomes is crucial for genome function. Here, we uncover a role for a conserved bromodomain AAA-ATPase, Abo1, in the maintenance of nucleosome architecture in fission yeast. Cells lacking abo1(+) experience both a reduction and mis-positioning of nucleosomes at transcribed sequences in addition to increased intragenic transcription, phenotypes that are hallmarks of defective chromatin re-establishment behind RNA polymerase II. Abo1 is recruited to gene sequences and associates with histone H3 and the histone chaperone FACT. Furthermore, the distribution of Abo1 on chromatin is disturbed by impaired FACT function. The role of Abo1 extends to some promoters and also to silent heterochromatin. Abo1 is recruited to pericentromeric heterochromatin independently of the HP1 ortholog, Swi6, where it enforces proper nucleosome occupancy. Consequently, loss of Abo1 alleviates silencing and causes elevated chromosome mis-segregation. We suggest that Abo1 provides a histone chaperone function that maintains nucleosome architecture genome-wide.BBSRC (Doctoral Training Grants) Medical Research Council National Institute for Health Research (NIHR) Newcastle Biomedical Research Centre based at Newcastle Upon Tyne Hospitals NHS Foundation Trust and Newcastle University Marie Curie International Incoming FellowshipIIF275280 EMBO Long Term FellowshipALTF 1491‐2010 The Wellcome Trust095021 Wellcome Trust core funding092076 NIA fellowshipNRSA F31‐AG038153 NIH R01GM084045 Cancer CenterCCSG 2 P30 CA21765; American Lebanese Syrian Associated Charities of St. Jude Children's Research Hospital; Wellcome Trust Senior Investigator Award; Wellcome Trust Institutional Strategic Support FundWT097835MF; Newcastle UniversityWT 097823/Z/11/

CpG island methylation is a common finding in colorectal cancer cell lines

Tumour cell lines are commonly used in colorectal cancer (CRC) research, including studies designed to assess methylation defects. Although many of the known genetic aberrations in CRC cell lines have been comprehensively described, no studies have been performed on their methylation status. In this study, 30 commonly used CRC cell lines as well as seven primary tumours from individuals with hereditary nonpolyposis colorectal cancer (HNPCC) were assessed for methylation at six CpG islands known to be hypermethylated in colorectal cancer: hMLH1, p16, methylated in tumour (MINT-)-1, -2, -12 and -31. The cell lines were also assessed for microsatellite instability (MSI), ploidy status, hMLH1 expression, and mutations in APC and Ki-ras. Methylation was frequently observed at all examined loci in most cell lines, and no differences were observed between germline-derived and sporadic cell lines. Methylation was found at MINT 1 in 63%, MINT 2 in 57%, MINT 12 in 71%, MINT 31 in 53%, p16 in 71%, and hMLH1 in 30% of cell lines. Overall only one cell line, SW1417, did not show methylation at any locus. Methylation was found with equal frequency in MSI and chromosomally unstable lines. MSI was over-represented in the cell lines relative to sporadic CRC, being detected in 47% of cell lines. The rate of codon 13 Ki-ras mutations was also over three times that expected from in vivo studies. We conclude that CpG island hypermethylation, whether acquired in vivo or in culture, is a ubiquitous phenomenon in CRC cell lines. We suggest that CRC cell lines may be only representative of a small subset of real tumours, and this should be taken into account in the use of CRC cell lines for epigenetic studies

Images in Medicine - Fryns Syndrome

A 17-year-old (G1P) Australian aboriginal mother delivered a male neonate weighing 2400 grams following a spontaneous vaginal delivery at term. Antenatal scan at 29 weeks' gestation had shown congenital diaphragmatic hernia (CDH) along with multiple anomalies suggestive of Fryns syndrome (Figure 1, 2). There was no polyhydramnios. Karyotyping was normal and alpha-foetoprotein was in normal range. The neonate was electively intubated in view of CDH (Apgar scores: 3 and 5 at 1 and 5 minutes respectively). Clinical examination revealed multiple congenital anomalies associated with right-sided CDH suggestive of Fryns syndrome. They included coarse facial features, hypertelorism, corneal clouding, broad nasal root, absent malformed right ear, rudimentary left ear with absent external auditory canal, very short neck, and a scaphoid abdomen due to the large CDH with herniation of liver in the thoracic cavity. The limb abnormalities included absent right radius, clinodactly, hypoplasia of the thumb, and long slender fingers, simian crease on right hand, and increased space between first and second toes. There were 11 ribs bilaterally and hemivertebrae were noted at C6 and T1 level. Echocardiography revealed large ventricular septal defect, atrial septal defect and left pulmonary artery could not be visualised. Head ultrasound revealed dilated lateral ventricles whereas renal scan was normal. Death occurred at 18 hours of age after withdrawal of life support following failure of maximal medical therapy for pulmonary hypoplasia with severe persistent pulmonary hypertension of the newborn. Withdrawal of life support was delayed mainly to allow appropriate counselling of the mother. Autopsy was not done as per the wish of the mother. There was no history of similar problems in the family