Nucleolar Expression and Chromosomal Associations in Robertsonian Spermatocytes of Mus musculus domesticus.

We studied and compared the nucleolar expression or nucleoli from specific bivalents in spermatocytes of the standard Mus musculus domesticus 2n=40, of Robertsonian (Rb) homozygotes 2n = 24 and heterozygotes 2n = 32. We analyzed 200 nuclear microspreads of each specific nucleolar chromosome and spermatocyte karyotype, using FISH to identify specific nucleolar bivalents, immunofluorescence for both fibrillarin of the nucleolus and the synaptonemal complex of the bivalents, and DAPI for heterochromatin. There was nucleolar expression in all the chromosomal conditions studied. By specific nucleolar bivalent, the quantitative relative nucleolar expression was higher in the bivalent 12 than in its derivatives, lower in the bivalent 15 than in its derivatives and higher in the bivalent 16 than its Rb derivatives. In the interactions between non-homologous chromosomal domains, the nucleolar bivalents were preferentially associated through pericentromeric heterochromatin with other bivalents of similar morphology and sometimes with other nucleolar bivalents. We suggest that the nucleolar expression in Rb nucleolar chromosomes is modified as a consequence of different localization of ribosomal genes (NOR) in the Rb chromosomes, its proximity to heterochromatin and its associations with chromosomes of the same morphology.

Simulating aggregates of bivalents in 2n = 40 mouse meiotic spermatocytes through inhomogeneous site percolation processes.

We show that an inhomogeneous Bernoulli site percolation process running upon a fullerene's dual [Formula: see text] can be used for representing bivalents attached to the nuclear envelope in mouse Mus M. Domesticus 2n = 40 meiotic spermatocytes during pachytene. It is shown that the induced clustering generated by overlapping percolation domains correctly reproduces the probability distribution observed in the experiments (data) after fine tuning the parameters.

Synaptic configuration of quadrivalents and their association with the XY bivalent in spermatocytes of Robertsonian heterozygotes of Mus domesticus.

BACKGROUND: The nuclear architecture of meiotic prophase spermatocytes is based on higher-order patterns of spatial associations among chromosomal domains and consequently is prone to modification by chromosomal rearrangements. We have shown that nuclear architecture is modified in spermatocytes of Robertsonian (Rb) homozygotes of Mus domesticus. In this study we analyse the synaptic configuration of the quadrivalents formed in the meiotic prophase of spermatocytes of mice double heterozygotes for the dependent Rb chromosomes: Rbs 11.16 and 16.17. RESULTS: Electron microscope spreads of 60 pachytene spermatocytes from four animals of Mus domesticus 2n = 38 were studied and their respective quadrivalents analysed in detail. Normal synaptonemal complex was found between arms 16 of the Rb metacentric chromosomes, telocentrics 11 and 17 and homologous arms of the Rb metacentric chromosomes. About 43% of the quadrivalents formed a synaptonemal complex between the heterologous short arms of chromosomes 11 and 17. This synaptonemal complex is bound to the nuclear envelope through a fourth synapsed telomere, thus dragging the entire quadrivalent to the nuclear envelope. About 57% of quadrivalents showed unsynapsed single axes in the short arms of the telocentric chromosomes. About 90% of these unsynapsed quadrivalents also showed a telomere-to-telomere association between one of the single axes of the telocentric chromosome 11 or 17 and the X chromosome single axis, which was otherwise normally paired with the Y chromosome. Nucleolar material was associated with two bivalents and with the quadrivalent. CONCLUSIONS: The spermatocytes of heterozygotes for dependent Rb chromosomes formed a quadrivalent where four chromosomes are synapsed together and bound to the nuclear envelope through four telomeres. The nuclear configuration is determined by the fourth shortest telomere, which drags the centromere regions and heterochromatin of all the chromosomes towards the nuclear envelope, favouring the reiterated encounter and eventual rearrangement between the heterologous chromosomes. The unsynapsed regions of quadrivalents are frequently bound to the single axis of the X chromosome, possibly perturbing chromatin condensation and gene expression.

Nuclear Architecture of Mouse Spermatocytes: Chromosome Topology, Heterochromatin, and Nucleolus.

The nuclear organization of spermatocytes in meiotic prophase I is primarily determined by the synaptic organization of the bivalents that are bound by their telomeres to the nuclear envelope and described as arc-shaped trajectories through the 3D nuclear space. However, over this basic meiotic organization, a spermatocyte nuclear architecture arises that is based on higher-ordered patterns of spatial associations among chromosomal domains from different bivalents that are conditioned by the individual characteristics of chromosomes and the opportunity for interactions between their domains. Consequently, the nuclear architecture is species-specific and prone to modification by chromosomal rearrangements. This model is valid for the localization of any chromosomal domain in the meiotic prophase nucleus. However, constitutive heterochromatin plays a leading role in shaping nuclear territories. Thus, the nuclear localization of nucleoli depends on the position of NORs in nucleolar bivalents, but the association among nucleolar chromosomes mainly depends on the presence of constitutive heterochromatin that does not affect the expression of the ribosomal genes. Constitutive heterochromatin and nucleoli form complex nuclear territories whose distribution in the nuclear space is nonrandom, supporting the hypothesis regarding the existence of a species-specific nuclear architecture in first meiotic prophase spermatocytes.

Synaptic configuration of quadrivalents and their association with the XY bivalent in spermatocytes of Robertsonian heterozygotes of Mus domesticus

BACKGROUND: The nuclear architecture of meiotic prophase spermatocytes is based on higher-order patterns of spatial associations among chromosomal domains and consequently is prone to modification by chromosomal rearrangements. We have shown that nuclear architecture is modified in spermatocytes of Robertsonian (Rb) homozygotes of Mus domesticus. In this study we analyse the synaptic configuration of the quadrivalents formed in the meiotic pro- phase of spermatocytes of mice double heterozygotes for the dependent Rb chromosomes: Rbs 11.16 and 16.17. RESULTS: Electron microscope spreads of 60 pachytene spermatocytes from four animals of Mus domesticus 2n = 38 were studied and their respective quadrivalents analysed in detail. Normal synaptonemal complex was found between arms 16 of the Rb metacentric chromosomes, telocentrics 11 and 17 and homologous arms of the Rb metacentric chromosomes. About 43% of the quadrivalents formed a synaptonemal complex between the heterologous short arms of chromosomes 11 and 17. This synaptonemal complex is bound to the nuclear envelope through a fourth synapsed telomere, thus dragging the entire quadrivalent to the nuclear envelope. About 57% of quadrivalents showed unsynapsed single axes in the short arms of the telocentric chromosomes. About 90% of these unsynapsed quadrivalents also showed a telomere-to-telomere association between one of the single axes of the telocentric chromosome 11 or 17 and the X chromosome single axis, which was otherwise normally paired with the Y chromosome. Nucleolar material was associated with two bivalents and with the quadrivalent. CONCLUSIONS: The spermatocytes of heterozygotes for dependent Rb chromosomes formed a quadrivalent where four chromosomes are synapsed together and bound to the nuclear envelope through four telomeres. The nuclear configuration is determined by the fourth shortest telomere, which drags the centromere regions and heterochromatin of all the chromosomes towards the nuclear envelope, favouring the reiterated encounter and eventual rearrangement between the heterologous chromosomes. The unsynapsed regions of quadrivalents are frequently bound to the single axis of the X chromosome, possibly perturbing chromatin condensation and gene expression.

Histology of the gonads of the hybrid Pseudoplatystoma punctifer X Leiarius marmoratus / Histologia das gônadas do híbrido Pseudoplatystoma punctifer X Leiarius marmoratus

Considering the rapid expansion of fish farming in intensive systems and the use of hybrids in Brazil, the study regarding the breeding capacity of the most recent hybrid is of ecological importance. If these animals are fertile, they may breed with the parental species in the wild and can negatively affect the genetic variability of the population (parental species in the wild). Fragments of the gonads were collected and submitted to histological evaluation. Histological cuts were stained with eosin/hematoxilin and toluidine, and slides were randomly selected for observation of three fields each animal, through light microscopy. Gonads of all fishes were paired structures of elongated shape in the abdominal cavity, covered by an albuginea tunic. Male juveniles presented primary spermatocytes while juvenile females presented chromatine nucleolus oocytes. Adult females presented chromatin-nucleolus oocytes, perinuclear, cortical alveoli, and vitellogenic oocytes visible in various sizes. The presence of oocytes in different stages and primary spermatocytes indicate that these fish may be fertile. Fish hybridization represents a threat to the conservation of native species.

Considerando a rápida expansão da piscicultura em sistemas intensivos e do uso de híbridos no Brasil, o estudo sobre a capacidade de reprodução do híbrido é de importância ecológica. Caso estes animais sejam férteis, podem afetar negativamente a variabilidade genética da população (espécies parentais em estado selvagem). Fragmentos das gônadas foram coletados e submetidos à avaliação histológica. Os cortes histológicos foram corados com eosina/hematoxilina e toluidina, e selecionados aleatoriamente para observação de três campos de cada animal, através de microscopia de luz. Gônadas de todos os peixes apresentaram-se como estruturas emparelhadas de forma alongada na cavidade abdominal, cobertas por uma túnica albugínea. Juvenis do sexo masculino apresentaram espermatócitos primários, enquanto as fêmeas juvenis apresentaram ovócitos cromatina nucléolo nos ovários. Fêmeas adultas apresentaram ovócitos cromatinanucléolo nos ovários, alvéolo cortical, perinuclear e vitelogênico, visíveis em vários tamanhos. A presença de ovócitos em diferentes fases e espermatócitos primários indicam que estes peixes podem ser férteis. A hibridação de peixes pode representar uma ameaça à conservação das espécies nativas.

Histology of the gonads of the hybrid Pseudoplatystoma punctifer X Leiarius marmoratus / Histologia das gônadas do híbrido Pseudoplatystoma punctifer X Leiarius marmoratus

Considering the rapid expansion of fish farming in intensive systems and the use of hybrids in Brazil, the study regarding the breeding capacity of the most recent hybrid is of ecological importance. If these animals are fertile, they may breed with the parental species in the wild and can negatively affect the genetic variability of the population (parental species in the wild). Fragments of the gonads were collected and submitted to histological evaluation. Histological cuts were stained with eosin/hematoxilin and toluidine, and slides were randomly selected for observation of three fields each animal, through light microscopy. Gonads of all fishes were paired structures of elongated shape in the abdominal cavity, covered by an albuginea tunic. Male juveniles presented primary spermatocytes while juvenile females presented chromatine nucleolus oocytes. Adult females presented chromatin-nucleolus oocytes, perinuclear, cortical alveoli, and vitellogenic oocytes visible in various sizes. The presence of oocytes in different stages and primary spermatocytes indicate that these fish may be fertile. Fish hybridization represents a threat to the conservation of native species.(AU)

Considerando a rápida expansão da piscicultura em sistemas intensivos e do uso de híbridos no Brasil, o estudo sobre a capacidade de reprodução do híbrido é de importância ecológica. Caso estes animais sejam férteis, podem afetar negativamente a variabilidade genética da população (espécies parentais em estado selvagem). Fragmentos das gônadas foram coletados e submetidos à avaliação histológica. Os cortes histológicos foram corados com eosina/hematoxilina e toluidina, e selecionados aleatoriamente para observação de três campos de cada animal, através de microscopia de luz. Gônadas de todos os peixes apresentaram-se como estruturas emparelhadas de forma alongada na cavidade abdominal, cobertas por uma túnica albugínea. Juvenis do sexo masculino apresentaram espermatócitos primários, enquanto as fêmeas juvenis apresentaram ovócitos cromatina nucléolo nos ovários. Fêmeas adultas apresentaram ovócitos cromatinanucléolo nos ovários, alvéolo cortical, perinuclear e vitelogênico, visíveis em vários tamanhos. A presença de ovócitos em diferentes fases e espermatócitos primários indicam que estes peixes podem ser férteis. A hibridação de peixes pode representar uma ameaça à conservação das espécies nativas.(AU)

Robertsonian chromosomes and the nuclear architecture of mouse meiotic prophase spermatocytes

BACKGROUND: The nuclear architecture of meiotic prophase spermatocytes is based on higher-order patterns of spatial associations among chromosomal domains from different bivalents. The meiotic nuclear architecture depends on the chromosome characteristics and consequently is prone to modification by chromosomal rearrangements. In this work, we consider Mus domesticus spermatocytes with diploid chromosome number 2n = 40, all telocentric, and investigate a possible modification of the ancestral nuclear architecture due to the emergence of derived Rb chromosomes, which may be present in the homozygous or heterozygous condition. RESULTS: In the 2n = 40 spermatocyte nuclei random associations mediated by pericentromeric heterochromatin among the 19 telocentric bivalents ocurr at the nuclear periphery. The observed frequency of associations among them, made distinguishable by specific probes and FISH, seems to be the same for pairs that may or may not form Rb chromosomes. In the homozygote Rb 2n = 24 spermatocytes, associations also mediated by pericentromeric heterochromatin occur mainly between the three telocentric or the eight metacentric bivalents themselves. In heterozygote Rb 2n = 32 spermatocytes all heterochromatin is localized at the nuclear periphery, yet associations are mainly observed among the three telocentric bivalents and between the asynaptic axes of the trivalents. CONCLUSIONS: The Rb chromosomes pose sharp restrictions for interactions in the 2n = 24 and 2n = 32 spermatocytes, as compared to the ample possibilities for interactions between bivalents in the 2n = 40 spermatocytes. Undoubtedly the emergence of Rb chromosomes changes the ancestral nuclear architecture of 2n = 40 spermatocytes since they establish new types of interactions among chromosomal domains, particularly through centromeric and heterochromatic regions at the nuclear periphery among telocentric and at the nuclear center among Rb metacentric ones.

Model of chromosome associations in Mus domesticus spermatocytes

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.