Dataset Information

Non-Random Distribution of Reciprocal Translocation Breakpoints in the Pig Genome.

ABSTRACT: Balanced chromosome rearrangements are one of the main etiological factors contributing to hypoprolificacy in the domestic pig. Amongst domestic animals, the pig is considered to have the highest prevalence of chromosome rearrangements. To date over 200 unique chromosome rearrangements have been identified. The factors predisposing pigs to chromosome rearrangements, however, remain poorly understood. Nevertheless, here we provide empirical evidence which sustains the notion that there is a non-random distribution of chromosomal rearrangement breakpoints in the pig genome. We sought to establish if there are structural chromosome factors near which rearrangement breakpoints preferentially occur. The distribution of rearrangement breakpoints was analyzed across three level, chromosomes, chromosome arms, and cytogenetic GTG-bands (G-banding using trypsin and giemsa). The frequency of illegitimate exchanges (e.g., reciprocal translocations) between individual chromosomes and chromosome arms appeared to be independent of chromosome length and centromere position. Meanwhile chromosome breakpoints were overrepresented on some specific G-bands, defining chromosome hotspots for ectopic exchanges. Cytogenetic band level factors, such as the length of bands, chromatin density, and presence of fragile sites, were associated with the presence of translocation breakpoints. The characteristics of these bands were largely similar to that of hotspots in the human genome. Therefore, those hotspots are proposed as a starting point for future molecular analyses into the genomic landscape of porcine chromosome rearrangements.

SUBMITTER: Donaldson B

PROVIDER: S-EPMC6826608 | biostudies-literature | 2019 Sep

REPOSITORIES: biostudies-literature

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Non-Random Distribution of Reciprocal Translocation Breakpoints in the Pig Genome.

Donaldson Brendan B Villagomez Daniel A F DAF Revay Tamas T Rezaei Samira S King W Allan WA

Genes 20190930 10

Balanced chromosome rearrangements are one of the main etiological factors contributing to hypoprolificacy in the domestic pig. Amongst domestic animals, the pig is considered to have the highest prevalence of chromosome rearrangements. To date over 200 unique chromosome rearrangements have been identified. The factors predisposing pigs to chromosome rearrangements, however, remain poorly understood. Nevertheless, here we provide empirical evidence which sustains the notion that there is a non-r ...[more]

PMID: 31575040

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Project description:Balanced constitutional reciprocal translocations are the most common structural chromosomal rearrangements identiﬁed in man and pigs. Carriers are generally phenotypically normal, but such rearrangements frequently lead to reproductive disorders. In reciprocal translocation heterozygotes, the homologous regions of the normal and derivative chromosomes involved in the rearrangement pair during the prophase of the first meiotic division, thanks to the synaptonemal complex (SC), and form a particular structure called quadrivalent. In some cases, chromosomal regions (within the quadrivalent) remain unsynapsed, especially around the breakpoints, which may trigger meiosis checkpoints leading to spermatogenesis arrest at the pachytene stage. Several hypotheses have been proposed to explain such effects of pairing failure on gametogenesis. The first one is an altered transcription of the genes located on the unpaired segments. Indeed, studies conducted in mice revealed a transcriptional repression of unpaired regions by a specific mechanism called “Meiotic Silencing of Unsynapsed Chromatin” (MSUC) in individuals with a partial or total spermatogenesis arrest (Turner et al., 2005). If some genes necessary for the proper course of meiosis are located in such unsynapsed genomic regions, MSUC may result in an arrest of the meiotic division. Secondly, associations between the “quadrivalent” and the XY bivalent which is transcriptionally silenced by a phenomenon known as meiotic sex chromosome inactivation (MSCI, (Turner, 2007) were also observed in individuals with altered semen parameters (azoospermic or oligospemic) (Oliver-Bonet et al., 2005; Sciurano et al., 2007a, 2012). Such an association could result in a partial reactivation of the XY body (XYB) leading to the expression of some genes located on the X chromosome (Lifschytz and Lindsley, 1972), or result in the spreading of the XYB inactivation towards the autosomal segments attached to the XYB, without reactivation of the latter (Jaafar et al., 1993). Beyond the potential spermatogenesis failure mentioned above, reciprocal translocations are systematically responsible for the production of genetically unbalanced gametes. Here we report the detailed analysis of the whole meiotic process (from spermatocytes to spermatozoa) in the case of a constitutional balanced reciprocal translocation responsible for severe oligoasthenoteratospermia.

Project description:Balanced constitutional reciprocal translocations are the most common structural chromosomal rearrangements identiï¬ed in man and pigs. Carriers are generally phenotypically normal, but such rearrangements frequently lead to reproductive disorders. In reciprocal translocation heterozygotes, the homologous regions of the normal and derivative chromosomes involved in the rearrangement pair during the prophase of the first meiotic division, thanks to the synaptonemal complex (SC), and form a particular structure called quadrivalent. In some cases, chromosomal regions (within the quadrivalent) remain unsynapsed, especially around the breakpoints, which may trigger meiosis checkpoints leading to spermatogenesis arrest at the pachytene stage. Several hypotheses have been proposed to explain such effects of pairing failure on gametogenesis. The first one is an altered transcription of the genes located on the unpaired segments. Indeed, studies conducted in mice revealed a transcriptional repression of unpaired regions by a specific mechanism called âMeiotic Silencing of Unsynapsed Chromatinâ (MSUC) in individuals with a partial or total spermatogenesis arrest (Turner et al., 2005). If some genes necessary for the proper course of meiosis are located in such unsynapsed genomic regions, MSUC may result in an arrest of the meiotic division. Secondly, associations between the âquadrivalentâ and the XY bivalent which is transcriptionally silenced by a phenomenon known as meiotic sex chromosome inactivation (MSCI, (Turner, 2007) were also observed in individuals with altered semen parameters (azoospermic or oligospemic) (Oliver-Bonet et al., 2005; Sciurano et al., 2007a, 2012). Such an association could result in a partial reactivation of the XY body (XYB) leading to the expression of some genes located on the X chromosome (Lifschytz and Lindsley, 1972), or result in the spreading of the XYB inactivation towards the autosomal segments attached to the XYB, without reactivation of the latter (Jaafar et al., 1993). Beyond the potential spermatogenesis failure mentioned above, reciprocal translocations are systematically responsible for the production of genetically unbalanced gametes. Here we report the detailed analysis of the whole meiotic process (from spermatocytes to spermatozoa) in the case of a constitutional balanced reciprocal translocation responsible for severe oligoasthenoteratospermia. Total RNA was extracted in 3 replicates from testicular biopsies control animals, from testicular biopsy of an oligospermic boar and from testicular biopsy of a severe oligo-astheno-teratospermic boar carrier of the trcp(1;14) reciprocal translocation.

Project description:Recent comprehensive sequence analysis of the maize genome now permits detailed discovery and description of all transposable elements (TEs) in this complex nuclear environment. Reiteratively optimized structural and homology criteria were used in the computer-assisted search for retroelements, TEs that transpose by reverse transcription of an RNA intermediate, with the final results verified by manual inspection. Retroelements were found to occupy the majority (>75%) of the nuclear genome in maize inbred B73. Unprecedented genetic diversity was discovered in the long terminal repeat (LTR) retrotransposon class of retroelements, with >400 families (>350 newly discovered) contributing >31,000 intact elements. The two other classes of retroelements, SINEs (four families) and LINEs (at least 30 families), were observed to contribute 1,991 and approximately 35,000 copies, respectively, or a combined approximately 1% of the B73 nuclear genome. With regard to fully intact elements, median copy numbers for all retroelement families in maize was 2 because >250 LTR retrotransposon families contained only one or two intact members that could be detected in the B73 draft sequence. The majority, perhaps all, of the investigated retroelement families exhibited non-random dispersal across the maize genome, with LINEs, SINEs, and many low-copy-number LTR retrotransposons exhibiting a bias for accumulation in gene-rich regions. In contrast, most (but not all) medium- and high-copy-number LTR retrotransposons were found to preferentially accumulate in gene-poor regions like pericentromeric heterochromatin, while a few high-copy-number families exhibited the opposite bias. Regions of the genome with the highest LTR retrotransposon density contained the lowest LTR retrotransposon diversity. These results indicate that the maize genome provides a great number of different niches for the survival and procreation of a great variety of retroelements that have evolved to differentially occupy and exploit this genomic diversity.

Dataset Information

Non-Random Distribution of Reciprocal Translocation Breakpoints in the Pig Genome.

Publications

Non-Random Distribution of Reciprocal Translocation Breakpoints in the Pig Genome.

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