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H Scherthan

Publications and source records attributed to H Scherthan.

At least 19 recordsLinked to original sources
PubMed2007

Telomere attachment and clustering during meiosis.

Telomeres are important segments of chromosomes that protect chromosome ends from nucleolytic degradation and fusion. At meiosis telomeres display an unprecedented behavior which involves their attachment and motility along the nuclear envelope. The movements become restricted to a limited nuclear sector during the so-called bouquet stage, which is widely conserved among species. Recent observations suggest that telomere clustering involves actin and/or microtubules, and is altered in the presence of impaired recombinogenic and chromosome related functions. This review aims to provide an overview of what is currently known about meiotic telomere attachment, dynamics and regulation in synaptic meiosis.

Actins↗
PubMed2006

Mutations that affect meiosis in male mice influence the dynamics of the mid-preleptotene and bouquet stages.

Meiosis pairs and segregates homologous chromosomes and thereby forms haploid germ cells to compensate the genome doubling at fertilization. Homologue pairing in many eukaryotic species depends on formation of DNA double strand breaks (DSBs) during early prophase I when telomeres begin to cluster at the nuclear periphery (bouquet stage). By fluorescence in situ hybridization criteria, we observe that mid-preleptotene and bouquet stage frequencies are altered in male mice deficient for proteins required for recombination, ubiquitin conjugation and telomere length control. The generally low frequencies of mid-preleptotene spermatocytes were significantly increased in male mice lacking recombination proteins SPO11, MEI1, MLH1, KU80, ubiquitin conjugating enzyme HR6B, and in mice with only one copy of the telomere length regulator Terf1. The bouquet stage was significantly enriched in Atm(-/-), Spo11(-/-), Mei1(m1Jcs/m1Jcs), Mlh1(-/-), Terf1(+/-) and Hr6b(-/-) spermatogenesis, but not in mice lacking recombination proteins DMC1 and HOP2, the non-homologous end-joining DNA repair factor KU80 and the ATM downstream effector GADD45a. Mice defective in spermiogenesis (Tnp1(-/-), Gmcl1(-/-), Asm(-/-)) showed wild-type mid-preleptotene and bouquet frequencies. A low frequency of bouquet spermatocytes in Spo11(-/-)Atm(-/-) spermatogenesis suggests that DSBs contribute to the Atm(-/-)-correlated bouquet stage exit defect. Insignificant changes of bouquet frequencies in mice with defects in early stages of DSB repair (Dmc1(-/-), Hop2(-/-)) suggest that there is an ATM-specific influence on bouquet stage duration. Altogether, it appears that several pathways influence telomere dynamics in mammalian meiosis.

Animals↗
PubMed2006

Factors directing telomere dynamics in synaptic meiosis.

Meiosis creates haploid cells from diploid progenitors. Homologous chromosomes are moved, paired and segregated from each other in a specialized meiosis I division. A second division that lacks a preceding S-phase produces haploid cells. In prophase I, chromosomes attach with their telomeres to the nuclear envelope and undergo oscillating movements that become restricted to a limited nuclear sector during the widely conserved bouquet stage. Recent observations in budding yeast meiosis suggest that telomere clustering depends on actin, whereas exit from the bouquet stage requires meiotic cohesin. Telomere clustering may also be modulated by progression in recombination. These observations suggest that the unique meiotic nuclear topology and telomere dynamics are regulated at different levels.

Actins↗
PubMed2005

Chromosome 18 pairing behavior in human trisomic oocytes. Presence of an extra chromosome extends bouquet stage.

Little is known about the first meiotic prophase stages in the human female because these occur during fetal life, and only a few studies have addressed aneuploid human oocytes. In this paper, the synaptic process in the meiotic prophase in three 47, XX+18 cases is analyzed. A complete study of the dynamics of centromeres and telomeres, cohesin core and synapsis development in aneuploid female meiosis was performed. Investigation of chromosome dynamics in prophase of trisomy 18 oocytes show that these events follow the major patterns seen earlier in euploid oocytes. However, there is a significant delay in the resolution of bouquet topology which could relate to the presence of a surplus chromosome 18 axial element in zygotene oocytes. Pachytene oocytes displayed normal synapsis among the three chromosome 18s. However, in some oocytes the surplus chromosome 18 core was aligned to the bivalent 18. As ataxia telangiectasia and Rad3 related kinase (ATR) has been described as a marker for late-pairing chromosomes in mice, ATR distribution was analyzed in human meiocytes--spermatocytes, euploid oocytes and trisomic oocytes. In contrast to the observations made in mice, no preferential staining for late-pairing chromosomes was observed in humans. In the cases studied, bivalent synapses progressed as in a normal ovary, contrasting with the hypothesis that a surplus chromosome can modify pairing of other chromosomes.

Ataxia Telangiectasia Mutated Proteins↗
PubMed2004

Female-specific features of recombinational double-stranded DNA repair in relation to synapsis and telomere dynamics in human oocytes.

Chromosome segregation errors are a significant cause of aneuploidy among human neonates and often result from errors in female meiosis that occur during fetal life. For the latter reason, little is known about chromosome dynamics during female prophase I. Here, we analyzed chromosome reorganization, and centromere and telomere dynamics in meiosis in the human female by immunofluorescent staining of the SYCP3 and SYCP1 synaptonemal complex proteins and the course of recombinational DNA repair by IF of phospho-histone H2A.X (gamma-H2AX), RPA and MLH1 recombination proteins. We found that SYCP3, but not SYCP1, aggregates appear in the preleptotene nucleus and some persist up to pachytene. Telomere clustering (bouquet stage) in oocytes lasted from late-leptotene to early pachytene-significantly longer than in the male. Leptotene and zygotene oocytes and spermatocytes showed strong gamma-H2AX labeling, while gamma-H2AX patches, which colocalized with RPA, were present on SYCP1-tagged pachytene SCs. This was rarely seen in the male and may suggest that synapsis installs faster with respect to progression of recombinational double-strand break repair or that the latter is slower in the female. It is speculated that the presence of gamma-H2AX into pachytene highlights female-specific peculiarities of recombination, chromosome behavior and checkpoint control that may contribute to female susceptibility for aneuploidy.

Adaptor Proteins, Signal Transducing↗
PubMed2003

Knockout mice provide novel insights into meiotic chromosome and telomere dynamics.

Meiosis is a succession of two specialized cell divisions that leads to the formation of gametes and thereby compensates for genome doubling at fertilization. During the extended prophase of the first meiotic division chromosomes assemble protein cores (axial elements) that attach their ends to the nuclear envelope. These ends transiently gather at a limited sector of the nuclear periphery (bouquet stage) at a time when meiotic recombination is initiated and when chromosomes initiate stable pairing (synapsis). This review discusses novel insights into the relation between recombinational DNA repair and meiotic telomere dynamics that have arrived from recent studies of transchromosomal mice and knockout mice. Analysis of mice deficient for A-type lamins, histone H2AX, Suv39h HMTases, and the AE protein SYCP3 suggests that entry into prophase I requires heterochromatin integrity and lamin A expression. Initiation of meiotic telomere clustering represents an early recombination-independent event in first meiotic prophase, while exit from the bouquet stage depends on signals that emanate from the progress of recombinational DNA repair as sensed by ATM kinase and relayed through histone H2AX.

Animals↗
PubMed2002

Genomic structure, conservation and FISH mapping of the Rattus norvegicus Adprt gene.

Poly(ADP-ribose) polymerase 1 (PARP-1) lies at the basis of a DNA-interacting protein family that maintains genome integrity. Here we describe the genomic organisation of rat PARP-1 gene (Adprt), refine its assignment to rat chromosome (RNO) 13q25-->q26 by FISH and compare its genomic organisation between rat, mouse and human. It appears that in human, mouse and rat Adprt consists of 23 similar-sized exons with well-conserved intron and exon borders. Adprt orthologs map to homologous chromosome regions at the termini of the q-arms of human and mouse chromosomes 1 and rat 13, with gene order being conserved between the rodents. Kimura protein distance comparison with human PARP-1 as reference revealed the bovine protein to be the least conserved with 10.3 substitutions per 100 amino acids, followed by rat (8.6) and mouse (8.4).

ADP Ribose Transferases↗
PubMed2001

Loss of the Suv39h histone methyltransferases impairs mammalian heterochromatin and genome stability.

Histone H3 lysine 9 methylation has been proposed to provide a major "switch" for the functional organization of chromosomal subdomains. Here, we show that the murine Suv39h histone methyltransferases (HMTases) govern H3-K9 methylation at pericentric heterochromatin and induce a specialized histone methylation pattern that differs from the broad H3-K9 methylation present at other chromosomal regions. Suv39h-deficient mice display severely impaired viability and chromosomal instabilities that are associated with an increased tumor risk and perturbed chromosome interactions during male meiosis. These in vivo data assign a crucial role for pericentric H3-K9 methylation in protecting genome stability, and define the Suv39h HMTases as important epigenetic regulators for mammalian development.

Aneuploidy↗
PubMed2001

Asynchronous chromosome pairing in male meiosis of the rat (Rattus norvegicus).

Premeiotic and meiotic chromosome distribution was studied in rat testes suspensions by a triple-color fluorescent staining protocol which allows simultaneous visual inspection of two chromosomal targets highlighted by FISH together with immunostained SCP3 synaptonemal complex (SC) proteins which are marked by a third, composite color. Triple labeling with rat chromosome (RNO) 4q and 19p specific probes and SCP3 staining disclosed that homologs are separated in premeiotic and leptotene nuclei. Pairing of homologous chromosome regions commenced during early zygotene, with pairing of the small metacentric chromosomes 19 preceding that of the distal region of the long arm of RNO4. Our results show that homolog association occurs during zygotene of rat spermatogenesis, with small and large chromosomes showing a considerable asynchrony. Comparison with pairing progression in meiosis of other mammals suggests that asynchronous chromosome pairing reflects size differences within a complement.

Animals↗
PubMed2001

A bouquet makes ends meet.

The 'chromosomal bouquet' is a polarized chromosomal arrangement that is highly conserved among eukaryotes. There have been many hypotheses about its role in the pairing of meiotic chromosomes, but until recently these have been difficult to test.

Animals↗
PubMed2001

HOPE fixation: a novel fixing method and paraffin-embedding technique for human soft tissues.

We have developed a novel method for tissue fixation, including subsequent paraffin-embedding and sectioning, that allows the complete pathological analysis of all types of human soft tissues. Furthermore, it maintains additional positive features relevant to immunohistochemistry and molecular pathology. The so-called HOPE-technique (Hepes-Glutamic acid buffer mediated Organic solvent Protection Effect) comprises a protection-solution with an organic buffer, acetone as the only dehydrating agent, and pure paraffin of 52-54 degrees C melting temperature. Although the exact mechanism of protection has still to be elucidated, it seems rather unlikely that chemical bindings occur during the whole process of fixation, which is described and compared with the standard formalin-paraffin technique. Essentially, HOPE-fixed sections show formalin-like morphology. However, the sections are somewhat difficult to handle because of their fragility. This is due to the absence of any type of protein cross-linking and the dynamic processes of immersion and outflow of the HOPE protection solution. HOPE-fixed sections provide an excellent preservation of proteins and antigenic structures for differential analysis by immunohistochemical and/or enzyme histochemical techniques. However, their most remarkable feature is the extremely low degradation of nucleic acids (DNA and RNA) combined with good results obtained by in situ hybridization techniques. In conclusion, HOPE fixation may become a valuable additional tool in modern pathology.

Cross-Linking Reagents↗
PubMed2001

Centromere and telomere redistribution precedes homologue pairing and terminal synapsis initiation during prophase I of cattle spermatogenesis.

Alterations in nuclear topology associated with meiotic chromosome pairing were studied in premeiotic cells and spermatocytes I of adult bovine males. To this end, we performed FISH with chromosome, pericentromeric satellite-DNA and telomere-specific probes in combination with immunostaining of synaptonemal complex proteins (SCP3, SCP1) on testis tissue sections. Nuclei of premeiotic cells (spermatogonia) exhibited a scattered telomere distribution while pericentromeres formed a few intranuclear clusters. We observed that the chromosome pairing process in cattle prophase I is preceded by repositioning of centromeres and telomeres to the nuclear periphery during preleptotene. Clustering of chromosome ends (bouquet formation) was observed during the transition from leptonema to zygonema and coincided with pairing of a sub-centromeric marker of bovine chromosomes 7. Dissolution of bouquet topology during zygonema left perinuclear telomeres scattered over the nuclear periphery at pachynema. SCP3 staining in frozen tissue sections revealed the appearance of this axial element protein in intranuclear aggregates during preleptotene, followed by extensive axial element formation during leptotene. Synapsis as revealed by SCP1 staining initiated peripherally at earliest zygotene, at this stage nuclei still contained numerous SCP3 clusters. Our observations reveal prominent non-homologous satellite-DNA associations in spermatogonia and indicate the conservation of topological features of the meiotic chromosome pairing process among mammals. The comparison of telomere dynamics in mouse and cattle prophase I suggests that a larger number of chromosomes prolongs the duration of the bouquet stage.

Animals↗
PubMed2000

Meiotic telomere protein Ndj1p is required for meiosis-specific telomere distribution, bouquet formation and efficient homologue pairing.

We have investigated the requirements for NDJ1 in meiotic telomere redistribution and clustering in synchronized cultures of Saccharomyces cerevisiae. On induction of wild-type meiosis, telomeres disperse from premeiotic aggregates over the nuclear periphery, and then cluster near the spindle pole body (bouquet arrangement) before dispersing again. In ndj1Delta meiocytes, telomeres are scattered throughout the nucleus and fail to form perinuclear meiosis-specific distribution patterns, suggesting that Ndj1p may function to tether meiotic telomeres to the nuclear periphery. Since ndj1Delta meiocytes fail to cluster their telomeres at any prophase stage, Ndj1p is the first protein shown to be required for bouquet formation in a synaptic organism. Analysis of homologue pairing by two-color fluorescence in situ hybridization with cosmid probes to regions on III, IX, and XI revealed that disruption of bouquet formation is associated with a significant delay (>2 h) of homologue pairing. An increased and persistent fraction of ndj1Delta meiocytes with Zip1p polycomplexes suggests that chromosome polarization is important for synapsis progression. Thus, our observations support the hypothesis that meiotic telomere clustering contributes to efficient homologue alignment and synaptic pairing. Under naturally occurring conditions, bouquet formation may allow for rapid sporulation and confer a selective advantage.

Centromere↗
PubMed2000

Double minutes and c-MYC amplification in acute myelogenous leukemia: Are they prognostic factors?

A case of acute myelogenous leukemia (AML) with double minutes (dmin) and X chromosome loss is presented. Using comparative genomic hybridization (CGH), a region of high-level DNA amplification was detected at 8q24, the locus of the c-MYC proto-oncogene. Fluorescence in situ hybridization (FISH) with a DNA probe specific for the human c-MYC gene confirmed the extrachromosomal amplification of this proto-oncogene in the dmin of the leukemic cells. During the course of the disease, three relapses occurred; two complete remissions could be achieved by treatment with various chemotherapy regimens. The patient's survival time of 25 months was considerably longer than in most reported cases of AML with extrachromosomal c-MYC amplification. Therefore, the present case challenges the view that the occurrence of dmin in AML is generally an indication of poor prognosis.

Adult↗
PubMed2000

Partial leptin receptor gene deletion in transgenic mice prevents expression of the membrane-bound isoforms except for Ob-Rc.

Examination of random insertional mutations in transgenic animals harbouring an abnormal phenotype contributes to the discovery of new genes and/or the understanding of already known genes. Here we describe a transgenic mouse line showing early-onset obesity as consequence of the transgene insertion. Molecular genetic analysis revealed a partial deletion of the leptin receptor (Lepr, Ob-R) gene including the coding sequences downstream of exon 17'. This defect prevents the expression of all described membrane-bound isoforms of Ob-R except for isoform Ob-Rc in the homozygous transgenic animals. Thus, this mouse model might be useful for the investigation of the function of the short Ob-R isoforms.

Animals↗
PubMed2000

Nuclear pore complexes in the organization of silent telomeric chromatin.

The functional regulation of chromatin is closely related to its spatial organization within the nucleus. In yeast, perinuclear chromatin domains constitute areas of transcriptional repression. These 'silent' domains are defined by the presence of perinuclear telomere clusters. The only protein found to be involved in the peripheral localization of telomeres is Yku70/Yku80. This conserved heterodimer can bind telomeres and functions in both repair of DNA double-strand breaks and telomere maintenance. These findings, however, do not address the underlying structural basis of perinuclear silent domains. Here we show that nuclear-pore-complex extensions formed by the conserved TPR homologues Mlp1 and Mlp2 are responsible for the structural and functional organization of perinuclear chromatin. Loss of MLP2 results in a severe deficiency in the repair of double-strand breaks. Furthermore, double deletion of MLP1 and MLP2 disrupts the clustering of perinuclear telomeres and releases telomeric gene repression. These effects are probably mediated through the interaction with Yku70. Mlp2 physically tethers Yku70 to the nuclear periphery, thus forming a link between chromatin and the nuclear envelope. We show, moreover, that this structural link is docked to nuclear-pore complexes through a cleavable nucleoporin, Nup145. We propose that, through these interactions, nuclear-pore complexes organize a nuclear subdomain that is intimately involved in the regulation of chromatin metabolism.

Antigens, Nuclear↗