ABSTRACT
Long intergenic non-coding RNAs (lincRNAs) are transcripts longer than 200 nucleotides which are transcribed from regions that do not overlap with protein coding sequences. Reproductive organs express high levels of lincRNAs, yet removal of many lincRNA genes with high and dynamic germline expression did not lead to fertility defects. It was previously suggested this stems from redundant roles of different lincRNA genes. We previously reported engineering C. elegans strains in which we deleted lincRNA genes with high and dynamic expression in the gonad. The individual mutations did not lead to major effects on fertility. Two of those lincRNA genes, linc-9 and linc-20, are highly homologous, suggesting they could perform redundant roles. Here we report that in the double mutant linc-9; linc-20 the brood size and embryonic lethality do not significantly differ from wild-type worms. This could be explained by either lack of fertility roles, or redundancy with other lincRNA genes.
ABSTRACT
During meiosis, gene expression is silenced in aberrantly unsynapsed chromatin and in heterogametic sex chromosomes. Initiation of sex chromosome silencing is disrupted in meiocytes with sex chromosome-autosome translocations. To determine whether this is due to aberrant synapsis or loss of continuity of sex chromosomes, we engineered Caenorhabditis elegans nematodes with non-translocated, bisected X chromosomes. In early meiocytes of mutant males and hermaphrodites, X segments are enriched with euchromatin assembly markers and active RNA polymerase II staining, indicating active transcription. Analysis of RNA-seq data showed that genes from the X chromosome are upregulated in gonads of mutant worms. Contrary to previous models, which predicted that any unsynapsed chromatin is silenced during meiosis, our data indicate that unsynapsed X segments are transcribed. Therefore, our results suggest that sex chromosome chromatin has a unique character that facilitates its meiotic expression when its continuity is lost, regardless of whether or not it is synapsed.
Subject(s)
Caenorhabditis elegans/genetics , Gene Silencing , Meiosis/genetics , X Chromosome/genetics , Animals , Caenorhabditis elegans Proteins/genetics , Caenorhabditis elegans Proteins/metabolism , Cell Cycle Proteins/genetics , Cell Cycle Proteins/metabolism , Chromatin/genetics , Chromosome Pairing/genetics , Female , Germ Cells/cytology , Germ Cells/metabolism , Histones/metabolism , In Situ Hybridization, Fluorescence , Male , Microscopy, Fluorescence , Transcription, GeneticABSTRACT
Long intergenic non-coding RNAs (lincRNAs) are transcripts longer than 200 nucleotides that are transcribed from non-coding loci yet undergo biosynthesis similar to coding mRNAs. The disproportional number of lincRNAs expressed in testes suggests that lincRNAs are important during gametogenesis, but experimental evidence has implicated very few lincRNAs in this process. We took advantage of the relatively limited number of lincRNAs in the genome of the nematode Caenorhabditis elegans to systematically analyse the functions of lincRNAs during meiosis. We deleted six lincRNA genes that are highly and dynamically expressed in the C. elegans gonad and tested the effects on central meiotic processes. Surprisingly, whereas the lincRNA deletions did not strongly impact fertility, germline apoptosis, crossovers, or synapsis, linc-4 was required for somatic growth. Slower growth was observed in linc-4-deletion mutants and in worms depleted of linc-4 using RNAi, indicating that linc-4 transcripts are required for this post-embryonic process. Unexpectedly, analysis of worms depleted of linc-4 in soma versus germline showed that the somatic role stems from linc-4 expression in germline cells. This unique feature suggests that some lincRNAs, like some small non-coding RNAs, are required for germ-soma interactions.
Subject(s)
Caenorhabditis elegans/genetics , Computational Biology , Germ Cells/metabolism , RNA, Long Noncoding/genetics , Animals , Computational Biology/methods , Fertility/genetics , Gene Deletion , Gene Expression Profiling/methods , Gene Expression Regulation , Gonads/metabolism , Meiosis/genetics , TranscriptomeABSTRACT
During meiosis, a series of evolutionarily conserved events allow for reductional chromosome division, which is required for sexual reproduction. Although individual meiotic processes have been extensively studied, we currently know far less about how meiosis is regulated and coordinated. In the Caenorhabditis elegans gonad, mitogen-activated protein kinase (MAPK) signaling drives oogenesis while undergoing spatial activation and deactivation waves. However, it is currently unclear how MAPK activation is governed and how it facilitates the progression of oogenesis. Here, we show that the oocyte and germline-related 2 (ogr-2) gene affects proper progression of oogenesis. Complete deletion of ogr-2 results in delayed meiotic entry and late spatial onset of double-strand break repair. Elevated levels of apoptosis are observed in this mutant, independent of the meiotic canonical checkpoints; however, they are dependent on the MAPK terminal member MPK-1/ERK. MPK-1 activation is elevated in diplotene in ogr-2 mutants and its aberrant spatial activation correlates with stages where meiotic progression defects are evident. Deletion of ogr-2 significantly reduces the expression of lip-1, a phosphatase reported to repress MPK-1, which is consistent with OGR-2 localization at chromatin in germ cells. We suggest that OGR-2 modulates the expression of lip-1 to promote the timely progression of meiosis through MPK-1 spatial deactivation.
