Biology subjects

Adams, I. R.

Publications and source records attributed to Adams, I. R..

5 recordsLinked to original sources

bioRxiv2018

Slow transcriptional elongation causes embryonic lethality and perturbs kinetic coupling of long neural genes

Alternative splicing (AS) is a highly regulated process that increases protein diversity and is critical for cell differentiation and development. The rate of RNA Polymerase II (RNAPII) elongation has an important role in the control of AS. We generated mouse embryonic stem cells (ESCs) knocked-in for a slow elongating form of RNAPII and show that a reduced transcriptional elongation rate causes early embryonic lethality in mice and impairs the differentiation of ESCs into the neural lineage. The reduced elongation rate caused changes in splicing and in gene expression in ESCs and along the pathway of neuronal differentiation. In particular, we found a crucial role for RNAPII elongation rate in transcription and splicing of long neuronal genes involved in synapse signaling. The impact of the kinetic coupling of RNAPII elongation rate with AS is more predominant in ESC-differentiated neurons than in pluripotent cells. Our results demonstrate the requirement for an appropriate transcriptional elongation rate to ensure proper gene expression and to regulate AS during development.

molecular biology↗

bioRxiv2017

Tex19.1 Restricts LINE-1 Mobilisation in Mouse Embryonic Stem Cells

Mobilisation of retrotransposons to new genomic locations is a significant driver of mammalian genome evolution. In humans, retrotransposon mobilisation is mediated primarily by proteins encoded by LINE-1 (L1) retrotransposons, which mobilise in pluripotent cells early in development. Here we show that TEX19.1, which is induced by developmentally programmed DNA hypomethylation, can directly interact with the L1-encoded protein L1-ORF1p, stimulate its polyubiquitylation and degradation, and restrict L1 mobilisation. We also show that TEX19.1 likely acts, at least in part, through promoting the activity of the E3 ubiquitin ligase UBR2 towards L1-ORF1p. Moreover, we show that loss of Tex19.1 increases L1-ORF1p levels and mobilisation of L1 reporters in pluripotent mouse embryonic stem cells implying that Tex19.1 prevents new retrotransposition-mediated mutations from arising in the germline genome. These data show that post-translational regulation of L1 retrotransposons plays a key role in maintaining trans-generational genome stability in the epigenetically dynamic developing mammalian germline.

genetics↗

bioRxiv2017

Tex19.1 Regulates Acetylated SMC3 Cohesin and Prevents Aneuploidy in Mouse Oocytes

Age-dependent oocyte aneuploidy, a major cause of Down syndrome, is associated with declining sister chromatid cohesion in postnatal oocytes. Here we show that cohesion in postnatal mouse oocytes is regulated by Tex19.1. We show that Tex19.1-/- oocytes have defects in the maintenance of chiasmata, mis-segregate their chromosomes during meiosis, and transmit aneuploidies to the next generation. By reconstituting aspects of this pathway in mitotic somatic cells, we show that Tex19.1 regulates an acetylated SMC3-marked subpopulation of cohesin by inhibiting the activity of the E3 ubiquitin ligase UBR2 towards specific substrates, and that UBR2 itself has a previously undescribed role in negatively regulating acetylated SMC3. Lastly, we show that acetylated SMC3 is associated with meiotic chromosome axes in oocytes, but that this is reduced in the absence of Tex19.1. These findings indicate that Tex19.1 maintains acetylated SMC3 and sister chromatid cohesion in postnatal oocytes, and prevents aneuploidy in the female germline.

genetics↗

bioRxiv2017

Tex19.1 Regulates Meiotic DNA Double Strand Break Frequency in Mouse Spermatocytes

Meiosis relies on the SPO11 endonuclease to generate the recombinogenic DNA double strand breaks (DSBs) required for homologous chromosome synapsis and segregation. The number of meiotic DSBs needs to be sufficient to allow chromosomes to search for and find their homologs, but not excessive to the point of causing genome instability. Here we report that meiotic DSB frequency in mouse spermatocytes is regulated by the mammal-specific gene Tex19.1. We show that the chromosome asynapsis previously reported in Tex19.1-/- spermatocytes is preceded by reduced numbers of recombination foci in leptotene and zygotene. Tex19.1 is required for the generation of normal levels of Spo11-dependent DNA damage during leptotene, but not for upstream events such as MEI4 foci formation or accumulation of H3K4me3 at recombination hotspots. Furthermore, we show that mice carrying mutations in the E3 ubiquitin ligase UBR2, a TEX19.1-interacting partner, phenocopy the Tex19.1-/- recombination defects. These data show that Tex19.1 and Ubr2 are required for mouse spermatocytes to generate sufficient meiotic DSBs to ensure that homology search is consistently successful, and reveal a hitherto unknown genetic pathway regulating meiotic DSB frequency in mammals.\n\nAuthor SummaryMeiosis is a specialised type of cell division that occurs during sperm and egg development to reduce chromosome number prior to fertilisation. Recombination is a key step in meiosis as it facilitates the pairing of homologous chromosomes prior to their reductional division, and generates new combinations of genetic alleles for transmission in the next generation. Regulating the amount of recombination is key for successful meiosis: too much will likely cause mutations, chromosomal re-arrangements and genetic instability, whereas too little causes defects in homologous chromosome pairing prior to the meiotic divisions. This study identifies a genetic pathway requiredto generate robust meiotic recombination in mouse spermatocytes. We show that male mice with mutations in Tex19.1 or Ubr2, which encodes an E3 ubiquitin ligase that interacts with TEX19.1, have defects in generating normal levels of meiotic recombination. We show that the defects in these mutants impact on the recombination process at the stage when programmed DNA double strand breaks are being made. This defect likely contributes to the chromosome synapsis and meiotic progression phenotypes previously described in these mutant mice. This study has implications for our understanding of how this fundamental aspect of genetics and inheritance is controlled.

genetics↗

bioRxiv2017

Defects in Meiotic Recombination Delay Progression Through Pachytene in Mouse Spermatocytes

During meiosis, recombination, synapsis, chromosome segregation and gene expression are coordinately regulated to ensure successful execution of this specialised cell division. In many model organisms, checkpoint controls can delay meiotic progression to allow defects or errors in these processes to be repaired or corrected. Mouse spermatocytes possess quality control checkpoints that eliminate cells with persistent irreparable defects in chromosome synapsis or recombination, and here we show that a spermatocyte checkpoint regulates progression through pachytene to accommodate delays in meiotic recombination. We have previously show that the appearance of early recombination foci is delayed in Tex19.1-/- spermatocytes during leptotene/zygotene, but some Tex19.1-/- spermatocytes still successfully synapse their chromosomes. Therefore, we have used autosomally synapsed Tex19.1-/- mouse spermatocytes to assess the consequences of delayed recombination on progression through pachytene. We show that these pachytene spermatocytes are enriched for early recombination foci. This skew is not accompanied by cell death and likely reflects delays in the generation and/or maturation of recombination foci. Moreover, patterns of axis elongation, chromatin modifications, and histone H1t expression are also all skewed towards earlier substages of pachytene suggesting these events are co-ordinately regulated. Importantly, the delay in histone H1t expression in response to loss of Tex19.1 does not occur in a Spo11 mutant background, suggesting that histone H1t expression is being delayed by a recombination-dependent checkpoint. These data indicate that a recombination-dependent checkpoint operates in mouse spermatocytes that can alter progression through pachytene to accommodate spermatocytes with some types of recombination defect.

genetics↗