Jesús Page

Universidad Autónoma de Madrid, Madrid, Madrid, Spain

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Publications (33)125.68 Total impact

  • [show abstract] [hide abstract]
    ABSTRACT: The cohesin complex plays a key role for the maintenance of sister chromatid cohesion and faithful chromosome segregation in both mitosis and meiosis. This complex is formed by two structural maintenance of chromosomes protein family (SMC) subunits and two non-SMC subunits: an α-kleisin subunit SCC1/RAD21/REC8 and an SCC3-like protein. Several studies carried out in different species have revealed that the distribution of the cohesin subunits along the chromosomes during meiotic prophase I is not regular and that some subunits are distinctly incorporated at different cell stages. However, the accurate distribution of the different cohesin subunits in condensed meiotic chromosomes is still controversial. Here, we describe the dynamics of the cohesin subunits SMC1α, SMC3, RAD21 and SA1 during both meiotic divisions in grasshoppers. Although these subunits show a similar patched labelling at the interchromatid domain of metaphase I bivalents, SMCs and non-SMCs subunits do not always colocalise. Indeed, SA1 is the only cohesin subunit accumulated at the centromeric region of all metaphase I chromosomes. Additionally, non-SMC subunits do not appear at the interchromatid domain in either single X or B chromosomes. These data suggest the existence of several cohesin complexes during metaphase I. The cohesin subunits analysed are released from chromosomes at the beginning of anaphase I, with the exception of SA1 which can be detected at the centromeres until telophase II. These observations indicate that the cohesin components may be differentially loaded and released from meiotic chromosomes during the first and second meiotic divisions. The roles of these cohesin complexes for the maintenance of chromosome structure and their involvement in homologous segregation at first meiotic division are proposed and discussed.
    Chromosoma 01/2013; · 3.34 Impact Factor
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    ABSTRACT: Synapsis and reciprocal recombination between sex chromosomes are restricted to the pseudoautosomal region. In some animal species, sex chromosomes do not present this region, although they utilize alternative mechanisms that ensure meiotic pairing and segregation. The subfamily Arvicolinae (Rodentia, Cricetidae) includes numerous species with achiasmate sex chromosomes. In order to know whether the mechanism involved in achiasmate segregation is an ancient feature in arvicolid species, we have compared the sex chromosomes of both the Mediterranean vole (Microtus duodecimcostatus) and the water vole (Arvicola terrestris). By means of immunofluorescence, we have found that sex chromosomes in M. duodecimcostatus are asynaptic and develop a synaptonemal complex-derived structure that mediates pairing and facilitates segregation. In A. terrestris, sex chromosomes are synaptic and chiasmate but also exhibit a synaptonemal complex-derived filament during anaphase I. Since phylogenetic relationships indicate that the synaptic condition is ancestral in arvicolids, this finding indicates that the mechanism for achiasmate sex chromosome segregation precedes the switching to the asynaptic condition. We discuss the origin of this synaptonemal complex-derived mechanism that, in turn, could counterbalance the disruption of homology in the sex chromosomes of those species.
    Chromosoma 05/2012; 121(5):433-46. · 3.34 Impact Factor
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    ABSTRACT: During the first meiotic prophase in male mammals, sex chromosomes undergo a program of transcriptional silencing called meiotic sex chromosome inactivation (MSCI). MSCI is triggered by accumulation of proteins like BRCA1, ATR, and γH2AX on unsynapsed chromosomes, followed by local changes on the sex chromatin, including histone modifications, incorporation of specific histone variants, non-histone proteins, and RNAs. It is generally thought that MSCI represents the transition of unsynapsed chromatin from a transcriptionally active state to a repressed state. However, transcription is generally low in the whole nucleus during the early stages of the first meiotic prophase, when markers of MSCI first appear, and is then reactivated globally during pachytene. Thus, an alternative possibility is that MSCI represents the targeted maintenance and/or reinforcement of a prior repressed state, i.e., a failure to reactivate. Here, we present an analysis of the temporal and spatial appearance of transcriptional and MSCI markers, as well as chromatin modifications related to transcriptional regulation. We show that levels of RNA pol II and histone H3 acetylated at lysine 9 (H3K9ac) are low during leptotene, zygotene, and early pachytene, but increase strongly in mid-pachytene, indicating that reactivation occurs with some delay after synapsis. However, while transcription markers appear abundantly on the autosomes at mid-pachytene, they are not directed to the sex chromosomes. Interestingly, we found that chromatin modifications related to transcriptional silencing and/or MSCI, namely, histone H3 trimethylated at lysine 9 (H3K9me3), histone H3 monomethylated at lysine 4 (H3K4me1), γH2AX, SUMO1, and XMR, appear on the sex chromosomes before autosomes become reactivated. These results suggest that the onset of MSCI during late zygotene and early pachytene may prevent sex chromosome reactivation during mid-pachytene instead of promoting inactivation de novo. Additionally, we found temporal differences between the X and Y chromosomes in the recruitment of DNA repair and MSCI markers, indicating a differential regulation of these processes. We propose that many of the meiotic defects attributed to failure to silence sex chromosomes could be interpreted as a more general process of transcriptional misregulation that occurs under certain pathological circumstances in zygotene and early pachytene.
    Chromosoma 02/2012; 121(3):307-26. · 3.34 Impact Factor
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    ABSTRACT: Great genome size (GS) variations described in desert-specialist octodontid rodents include diploid species ( Octomys mimax and Octodontomys gliroides ) and putative tetraploid species ( Tympanoctomys barrerae and Pipanacoctomys aureus ). Because of its high DNA content, elevated chromosome number, and gigas effect, the genome of T. barrerae is claimed to have resulted from tetraploidy. Alternatively, the origin of its GS has been attributed to the accumulation of repetitive sequences. To better characterize the extent and origin of these repetitive DNA, self-genomic in situ hybridization (self-GISH), whole-comparative genomic hybridization (W-CGH), and conventional GISH were conducted in mitotic and meiotic chromosomes. Self-GISH on T. barrerae mitotic plates together with comparative self-GISH (using its closest relatives) discriminate a pericentromeric and a telomeric DNA fraction. As most of the repetitive sequences are pericentromeric, it seems that the large GS of T. barrerae is not due to highly repeated sequences accumulated along chromosomes arms. W-CGH using red-labeled P. aureus DNA and green-labeled O. mimax DNA simultaneously on chromosomes of T. barrerae revealed a yellow-orange fluorescence over a repetitive fraction of the karyotype. However, distinctive red-only fluorescent signals were also detected at some centromeres and telomeres, indicating closer homology with the DNA sequences of P. aureus. Conventional GISH using an excess of blocking DNA from either P. aureus or O. mimax labeled only a fraction of the T. barrerae genome, indicating its double genome composition. These data point to a hybrid nature of the T. barrerae karyotype, suggesting a hybridization event in the origin of this species.
    Genome 02/2012; 55(2):105-17. · 1.65 Impact Factor
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    ABSTRACT: The house mouse is characterised by highly variable chromosome number due to the presence of Robertsonian (Rb) chromosomes. During meiosis in Rb heterozygotes, intricated chromosomal figures are produced, and many unsynapsed regions are present during the first prophase, triggering a meiotic silencing of unsynapsed chromatin (MSUC) in a similar mode to the sex chromosome inactivation. The presence of unsynapsed chromosome regions is associated with impaired spermatogenesis. Interestingly, in male mice carrying multiple Rb trivalents, the frequency of germ cell death, defective tubules, and altered sperm morphology decreases during aging. Here, we studied whether synapsis of trivalent chromosomes and MSUC are involved in this improvement. By immunocytochemistry, we analysed the frequency of unsynapsed chromosomes and of those positive to γH2AX (a marker of MSUC) labelling in spermatocytes of 3-, 5- and 7-month-old Rb heterozygotes. With aging, we observed a decrease of the frequency of unsynapsed chromosomes, of spermatocytes bearing them and of trivalents carrying γH2AX-negative unsynapsed regions. Our quantitative results show that both synapsis and MSUC processes are better accomplished during male aging, partially accounting for the improvement of spermatogenesis.
    Chromosome Research 01/2012; 20(2):269-78. · 2.85 Impact Factor
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    ABSTRACT: In the present study, and as a sincere tribute from the Cytogenetics teams from Madrid to Professor Máximo Drets on his 80th birthday, we have analyzed and compared 3 different grasshopper species with different synaptic patterns, a standard pattern, a second pattern with synapsis restricted to the proximal regions, and a third pattern with synapsis restricted to the distal regions. In the 3 species we have thoroughly analyzed the relationships among cohesin axis morphogenesis, formation of double strand breaks (DSBs) and recombination initiation. Our results demonstrate that in every case recombination initiation precedes synapsis, and that there is a direct relationship between the absence of meiotic recombination and the existence of particular unsynapsed chromosomal regions during prophase I. Based on our results we propose and discuss the mechanisms underlying the existence of incomplete synapsis and the localization of chiasma in wild species.
    Cytogenetic and Genome Research 04/2010; 128(1-3):139-51. · 1.84 Impact Factor
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    ABSTRACT: Understanding the spatial organization of the chromosomes in meiotic nuclei is crucial to our knowledge of the genome's functional regulation, stability and evolution. This study examined the nuclear architecture of Mus domesticus 2n=40 pachytene spermatocytes, analyzing the associations among autosomal bivalents via their Centromere Telomere Complexes (CTC). The study developed a nuclear model in which each CTC was represented as a 3D computer object. The probability of a given combination of associations among CTC was estimated by simulating a random distribution of 19 indistinguishable CTC over n indistinguishable "cells" on the nuclear envelope. The estimated association frequencies resulting from this numerical approach were similar to those obtained by quantifying actual associations in pachytene spermatocyte spreads. The nuclear localization and associations of CTC through the meiotic prophase in well-preserved nuclei were also analyzed. We concluded that throughout the meiotic prophase: 1) the CTC of autosomal bivalents are not randomly distributed in the nuclear space; 2) the CTC associate amongst themselves, probably at random, over a small surface of the nuclear envelope, at the beginning of the meiotic prophase; 3) the initial aggregation of centromere regions occurring in lepto-zygotene likely resolves into several smaller aggregates according to patterns of preferential partitioning; 4) these smaller aggregates spread over the inner face of the nuclear envelope, remaining stable until advanced stages of the meiotic prophase or even until the first meiotic division.
    Biological research 01/2010; 43(3):275-85. · 1.13 Impact Factor
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    ABSTRACT: The absence of homology between sex chromosomes in marsupials strongly influences their behaviour during male meiosis. The highly differentiated X and Y chromosomes perform a precise and specific meiotic program that includes pairing and segregation, but lacks the usual mechanisms of synapsis, recombination and chiasma formation that occur in the autosomes and also in the sex chromosomes of eutherian mammals. The most relevant feature of marsupial male meiosis is the development of a synaptonemal complex-derived structure called the dense plate (DP). This structure maintains the association between the asynaptic and achiasmatic sex chromosomes during the first meiotic division, contributing to the proper segregation of sex chromosomes into daughter cells. Comparison of the meiotic mechanism present in marsupials with those present in some eutherian mammals opens new perspectives concerning the origin of sex chromosomes and sex chromosome segregation in the ancestor of marsupials and placental mammals. Similarly, recent characterisation of the mechanisms involved in the inactivation of sex chromosomes during marsupial meiosis has led to the idea that somatic inactivation of sex chromosomes in mammals may have originated from the more ancient and conserved mechanism of meiotic sex chromosome inactivation. This clearly places marsupial meiosis at the heart of the discussion concerning sex chromosome evolution and the origin of gene dosage compensation in mammals. KeywordsDense plate-Inactivation-Marsupial-Meiosis-Sex chromosomes-Synapsis
    12/2009: pages 187-206;
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    ABSTRACT: Meiosis is a complex type of cell division that involves homologous chromosome pairing, synapsis, recombination, and segregation. When any of these processes is altered, cellular checkpoints arrest meiosis progression and induce cell elimination. Meiotic impairment is particularly frequent in organisms bearing chromosomal translocations. When chromosomal translocations appear in heterozygosis, the chromosomes involved may not correctly complete synapsis, recombination, and/or segregation, thus promoting the activation of checkpoints that lead to the death of the meiocytes. In mammals and other organisms, the unsynapsed chromosomal regions are subject to a process called meiotic silencing of unsynapsed chromatin (MSUC). Different degrees of asynapsis could contribute to disturb the normal loading of MSUC proteins, interfering with autosome and sex chromosome gene expression and triggering a massive pachytene cell death. We report that in mice that are heterozygous for eight multiple simple Robertsonian translocations, most pachytene spermatocytes bear trivalents with unsynapsed regions that incorporate, in a stage-dependent manner, proteins involved in MSUC (e.g., gammaH2AX, ATR, ubiquitinated-H2A, SUMO-1, and XMR). These spermatocytes have a correct MSUC response and are not eliminated during pachytene and most of them proceed into diplotene. However, we found a high incidence of apoptotic spermatocytes at the metaphase stage. These results suggest that in Robertsonian heterozygous mice synapsis defects on most pachytene cells do not trigger a prophase-I checkpoint. Instead, meiotic impairment seems to mainly rely on the action of a checkpoint acting at the metaphase stage. We propose that a low stringency of the pachytene checkpoint could help to increase the chances that spermatocytes with synaptic defects will complete meiotic divisions and differentiate into viable gametes. This scenario, despite a reduction of fertility, allows the spreading of Robertsonian translocations, explaining the multitude of natural Robertsonian populations described in the mouse.
    PLoS Genetics 09/2009; 5(8):e1000625. · 8.52 Impact Factor
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    ABSTRACT: We have analyzed in a true bug, Graphosoma italicum (Pentatomidae, Hemiptera), the temporal and functional relationships between recombination events, synapsis progression, and SMC1alpha and SMC3 cohesin axis maturation throughout the male first meiotic prophase. The localization of the histone variant histone H3 trimethylated at lysine 9 at chromosome ends has allowed us to determine the association of these heterochromatic domains through prophase I stages. Results highlighted that cohesins provide to be good markers for synapsis progression since the formation, morphology, and development of the SMC1alpha and SMC3 cohesin axes resemble the synaptonemal complex dynamics and, also, that in this species the initiation of recombination precedes synapsis. In addition, we have carried out an accurate cytological characterization of the diffuse stage, which takes place after pachytene, and also analyzed the presence of the cohesin subunits, SMC1alpha and SMC3, and the recombinase RAD51 at this stage. The mechanisms underlying the absence of SMC1alpha and SMC3 axes from the diffuse stage onwards are discussed.
    Chromosoma 07/2009; 118(5):575-89. · 3.34 Impact Factor
  • A Viera, J Page, J S Rufas
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    ABSTRACT: Most of the meiotic literature is based on species with monocentric chromosomes, however meiosis in protoctist, plant and animal species with holocentric chromosomes is less characterized. In some cases, an inverted meiotic sequence is claimed to occur, in which segregation of homologs is postponed until the second meiotic division. Additionally, other features also deserve interest, namely: (i) the different behavior of sex chromosomes if compared to that of the autosomes; (ii) the absence of a canonical kinetochore structure; (iii) the restriction of the kinetic activity to the chromosomal ends; (iv) the variations in the orientation of bivalents at the division plate, and (v) the possible occurrence of chiasma terminalization. Here we summarize the current knowledge on these topics in the meiosis of Hemiptera (Heteroptera) and present novel results that illustrate some of the special features mentioned above. We also point out the necessity of reviewing the term 'inverted meiosis' and propose some future prospects to study this peculiar meiosis.
    Genome dynamics 02/2009; 5:137-56.
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    ABSTRACT: In most eutherian mammals, sex chromosomes synapse and recombine during male meiosis in a small region called pseudoautosomal region. However in some species sex chromosomes do not synapse, and how these chromosomes manage to ensure their proper segregation is under discussion. Here we present a study of the meiotic structure and behavior of sex chromosomes in one of these species, the Mongolian gerbil (Meriones unguiculatus). We have analyzed the location of synaptonemal complex (SC) proteins SYCP1 and SYCP3, as well as three proteins involved in the process of meiotic recombination (RAD51, MLH1, and gamma-H2AX). Our results show that although X and Y chromosomes are associated at pachytene and form a sex body, their axial elements (AEs) do not contact, and they never assemble a SC central element. Furthermore, MLH1 is not detected on the AEs of the sex chromosomes, indicating the absence of reciprocal recombination. At diplotene the organization of sex chromosomes changes strikingly, their AEs associate end to end, and SYCP3 forms an intricate network that occupies the Y chromosome and the distal region of the X chromosome long arm. Both the association of sex chromosomes and the SYCP3 structure are maintained until metaphase I. In anaphase I sex chromosomes migrate to opposite poles, but SYCP3 filaments connecting both chromosomes are observed. Hence, one can assume that SYCP3 modifications detected from diplotene onwards are correlated with the maintenance of sex chromosome association. These results demonstrate that some components of the SC may participate in the segregation of achiasmate sex chromosomes in eutherian mammals.
    PLoS Genetics 12/2007; 3(11):e198. · 8.52 Impact Factor
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    ABSTRACT: The cohesin complexes play a key role in chromosome segregation during both mitosis and meiosis. They establish sister chromatid cohesion between duplicating DNA molecules during S-phase, but they also have an important role during postreplicative double-strand break repair in mitosis, as well as during recombination between homologous chromosomes in meiosis. An additional function in meiosis is related to the sister kinetochore cohesion, so they can be pulled by microtubules to the same pole at anaphase I. Data about the dynamics of cohesin subunits during meiosis are scarce; therefore, it is of great interest to characterize how the formation of the cohesin complexes is achieved in order to understand the roles of the different subunits within them. We have investigated the spatio-temporal distribution of three different cohesin subunits in prophase I grasshopper spermatocytes. We found that structural maintenance of chromosome protein 3 (SMC3) appears as early as preleptotene, and its localization resembles the location of the unsynapsed axial elements, whereas radiation-sensitive mutant 21 (RAD21) (sister chromatid cohesion protein 1, SCC1) and stromal antigen protein 1 (SA1) (sister chromatid cohesion protein 3, SCC3) are not visualized until zygotene, since they are located in the synapsed regions of the bivalents. During pachytene, the distribution of the three cohesin subunits is very similar and all appear along the trajectories of the lateral elements of the autosomal synaptonemal complexes. However, whereas SMC3 also appears over the single and unsynapsed X chromosome, RAD21 and SA1 do not. We conclude that the loading of SMC3 and the non-SMC subunits, RAD21 and SA1, occurs in different steps throughout prophase I grasshopper meiosis. These results strongly suggest the participation of SMC3 in the initial cohesin axis formation as early as preleptotene, thus contributing to sister chromatid cohesion, with a later association of both RAD21 and SA1 subunits at zygotene to reinforce and stabilize the bivalent structure. Therefore, we speculate that more than one cohesin complex participates in the sister chromatid cohesion at prophase I.
    PLoS Genetics 03/2007; 3(2):e28. · 8.52 Impact Factor
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    ABSTRACT: Marsupial sex chromosomes break the rule that recombination during first meiotic prophase is necessary to ensure reductional segregation during first meiotic division. It is widely accepted that in marsupials X and Y chromosomes do not share homologous regions, and during male first meiotic prophase the synaptonemal complex is absent between them. Although these sex chromosomes do not recombine, they segregate reductionally in anaphase I. We have investigated the nature of sex chromosome association in spermatocytes of the marsupial Thylamys elegans, in order to discern the mechanisms involved in ensuring their proper segregation. We focused on the localization of the axial/lateral element protein SCP3 and the cohesin subunit STAG3. Our results show that X and Y chromosomes never appear as univalents in metaphase I, but they remain associated until they orientate and segregate to opposite poles. However, they must not be tied by a chiasma since their separation precedes the release of the sister chromatid cohesion. Instead, we show they are associated by the dense plate, a SCP3-rich structure that is organized during the first meiotic prophase and that is still present at metaphase I. Surprisingly, the dense plate incorporates SCP1, the main protein of the central element of the synaptonemal complex, from diplotene until telophase I. Once sex chromosomes are under spindle tension, they move to opposite poles losing contact with the dense plate and undergoing early segregation. Thus, the segregation of the achiasmatic T. elegans sex chromosomes seems to be ensured by the presence in metaphase I of a synaptonemal complex-derived structure. This feature, unique among vertebrates, indicates that synaptonemal complex elements may play a role in chromosome segregation.
    PLoS Genetics 09/2006; 2(8):e136. · 8.52 Impact Factor
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    ABSTRACT: During first meiotic prophase, homologous chromosomes are held together by the synaptonemal complex, a tripartite proteinaceous structure that extends along the entire length of meiotic bivalents. While this feature is applicable for autosomes, sex chromosomes often escape from this rule. Many species present sex chromosomes that differ between them in their morphology, length, and gene content. Moreover, in some species, sex chromosomes appear in a single dose in one of the sexes. In all of these cases, the behavior of sex chromosomes during meiosis is conspicuously affected, and this includes the assembly and dynamics of the synaptonemal complex. We review in this study the structure of the synaptonemal complex in the sex chromosomes of three groups of organisms, namely: mammals, orthopterans, and hemipterans, which present different patterns of sex chromosome structure and behavior. Of special interest is the analysis of the organization of the axial/lateral elements of the synaptonemal complex in relation to other axial structures organized along meiotic chromosomes, mainly the cohesin axis. The differences found in the behavior of both axial structures reveal that while the organization of a cohesin axis along sex chromosomes is a conserved feature in most organisms and it shows very little morphological variations, the axial/lateral elements of the synaptonemal complex present a wide range of structural modifications on these chromosomes.
    Chromosoma 07/2006; 115(3):250-9. · 3.34 Impact Factor
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    ABSTRACT: Mitotic Centromere-Associated Kinesin (MCAK) is a member of the kinesin-13 subfamily of kinesin-related proteins. In mitosis, this microtubule-depolymerising kinesin seems to be implicated in chromosome segregation and in the correction of improper kinetochore-microtubule interactions, and its activity is regulated by the Aurora-B kinase. However, there are no published data on its behaviour and function during mammalian meiosis. We have analysed by immunofluorescence in squashed mouse spermatocytes, the distribution and possible function of MCAK, together with Aurora-B, during both meiotic divisions. Our results demonstrate that MCAK and Aurora-B colocalise at the inner domain of metaphase I centromeres. Thus, MCAK shows a "cone"-like three-dimensional distribution beneath and surrounding the closely associated sister kinetochores. During the second meiotic division, MCAK and Aurora-B also colocalise at the inner centromere domain as a band that joins sister kinetochores, but only during prometaphase II in unattached chromosomes. During chromosome congression to the metaphase II plate, MCAK relocalises and appears as a ring below each sister kinetochore. Aurora-B also relocalises to appear as a ring surrounding and beneath kinetochores but during late metaphase II. Our results demonstrate that the redistribution of MCAK at prometaphase II/metaphase II centromeres depends on tension across the centromere and/or on the interaction of microtubules with kinetochores. We propose that the perikinetochoric rings of MCAK and Aurora-B define a novel transient centromere domain at least in mouse chromosomes during meiosis. We discuss the possible functions of MCAK at the inner centromere domain and at the perikinetochoric ring during both meiotic divisions.
    PLoS Genetics 07/2006; 2(6):e84. · 8.52 Impact Factor
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    ABSTRACT: The relationship between meiotic recombination events and different patterns of pairing and synapsis has been analysed in prophase I spermatocytes of the grasshopper Stethophyma grossum, which exhibit very unusual meiotic characteristics, namely (1) the three shortest bivalents achieve full synapsis and do not show chiasma localisation; (2) the remaining eight bivalents show restricted synapsis and proximal chiasma localisation, and (3) the X chromosome remains unsynapsed. We have studied by means of immunofluorescence the localisation of the phosphorylated histone H2AX (gamma-H2AX), which marks the sites of double-strand breaks; the SMC3 cohesin subunit, which is thought to have a close relationship to the development of the axial element (a synaptonemal complex component); and the recombinase RAD51. We observed a marked nuclear polarization of both the maturation of SMC3 cohesin axis and the ulterior appearance of gamma-H2AX and RAD51 foci, these being exclusively restricted to those chromosomal regions that first form cohesin axis stretches. This polarised distribution of recombination events is maintained throughout prophase I over those autosomal regions that are undergoing, or about to undergo, synapsis. We propose that the restricted distribution of recombination events along the chromosomal axes in the spermatocytes is responsible for the incomplete presynaptic homologous alignment and, hence, for the partial synaptonemal complex formation displayed by most bivalents.
    Journal of Cell Science 08/2005; 118(Pt 13):2957-63. · 5.88 Impact Factor
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    ABSTRACT: Marsupials present a series of genetic and chromosomal features that are highly conserved in very distant species. One of these features is the absence of a homologous region between X and Y chromosomes. According to this genetic differentiation, sex chromosomes do not synapse during the first meiotic prophase in males, and a special structure, the dense plate, maintains sex chromosome association. In this report we present results on the process of meiotic sex chromosome pairing obtained from three different species, Thylamys elegans, Dromiciops gliroides, and Rhyncholestes raphanurus, representing the three orders of American marsupials. We have investigated the relationships between the axial structures organized along sex chromosomes and the formation of the dense plate. We found that in the three species the dense plate arises as a modification of sex chromosomal axial elements, but without the involvement of other meiotic axial structures, such as the cohesin axes. Considering the phylogenetic relationships among the marsupials studied here, our data reinforce the idea that the dense plate emerged early in marsupial evolution as an efficient mechanism to ensure the association of the nonhomologous sex chromosomes. This situation could have influenced the further evolution of sex chromosomes in marsupials.
    Genetics 07/2005; 170(2):793-9. · 4.39 Impact Factor
  • PLOS Genetics - PLOS GENET. 01/2005;
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    ABSTRACT: In seven mammalian species, including man, the position and number of nucleoli in pachytene spermatocyte nuclei were studied from electron microscope (EM) nuclear sections or bivalent microspreads. The number and position of the nucleolar organiser regions (NORs) in mitotic and meiotic chromosomes were also analysed, using silver staining techniques and in situ hybridisation protocols. The general organisation of pachytene spermatocyte nucleoli was almost the same, with only minor morphological differences between species. The terminal NORs of Thylamys elegans (Didelphoidea, Marsupialia), Dromiciops gliroides (Microbiotheridae, Marsupialia), Phyllotys osgoodi (Rodentia, Muridae) and man, always gave rise to peripheral nucleoli in the spermatocyte nucleus. In turn, the intercalated NORs from Octodon degus, Ctenomys opimus (Rodentia, Octodontidae) and Chinchilla lanigera (Rodentia, Cavidae), gave rise to central nucleoli. In species with a single nucleolar bivalent, just one nucleolus is formed, while in those with multiple nucleolar bivalents a variable number of nucleoli are formed by association of different nucleolar bivalents or NORs that occupy the same nuclear peripheral space (Phyllotis and man). It can be concluded that the position of each nucleolus within the spermatocyte nucleus is mainly dependent upon: (1) the position of the NOR in the nucleolar bivalent synaptonemal complex (SC), (2) the nuclear pathway of the nucleolar bivalent SC, being both telomeric ends attached to the nuclear envelope, and (3) the association between nucleolar bivalents by means of their NOR-nucleolar domains that occupy the same nuclear space. Thus, the distribution of nucleoli within the nuclear space of spermatocytes is non-random and it is consistent with the existence of a species-specific meiotic nuclear architecture.
    Genetica 08/2004; 121(3):219-28. · 1.68 Impact Factor

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469 Citations
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125.68 Total Impact Points

Institutions

  • 1996–2013
    • Universidad Autónoma de Madrid
      • Departamento de Biología
      Madrid, Madrid, Spain
  • 2003–2009
    • University of Santiago, Chile
      CiudadSantiago, Santiago, Chile
  • 2002–2005
    • University of Chile
      • • Instituto de Ciencias Biomédicas (ICBM)
      • • Programa de Genética Humana
      Santiago, Region Metropolitana de Santiago, Chile