Genes & genetic systems最新文献

Transposons were once thought to be junk repetitive DNA in the genome. However, their importance gradually became apparent as it became clear that they regulate gene expression, which is essential for organisms to survive, and that they are important factors in the driving force of evolution. Since there are multiple transposons in the genomes of all organisms, transposons have likely been activated and increased in copy number throughout their long history. This review focuses on environmental stress as a factor in transposon activation, paying particular attention to transposons in plants that are activated by environmental stresses. It is now known that plants respond to environmental stress in various ways, and correspondingly, many transposons respond to stress. The relationship between environmental stress and transposons is reviewed, including the mechanisms of their activation and the effects of transposon activation on host plants.

Mating-type (P or M) of fission yeast Schizosaccharomyces pombe is determined by the transcriptionally active mat1 cassette and is switched by gene conversion using a donor, either mat2 or mat3, located in an adjacent heterochromatin region (mating-type switching; MTS). In the switching process, heterochromatic donors of genetic information are selected based on the P or M cell type and on the action of two recombination enhancers, SRE2 promoting the use of mat2-P and SRE3 promoting the use of mat3-M, leading to replacement of the content of the expressed mat1 cassette. Recently, we found that the histone H3K4 methyltransferase complex Set1C participates in donor selection, raising the question of how a complex best known for its effects in euchromatin controls recombination in heterochromatin. Here, we report that the histone H2BK119 ubiquitin ligase complex HULC functions with Set1C in MTS, as mutants in the shf1, brl1, brl2 and rad6 genes showed defects similar to Set1C mutants and belonged to the same epistasis group as set1Δ. Moreover, using H3K4R and H2BK119R histone mutants and a Set1-Y897A catalytic mutant, we found that ubiquitylation of histone H2BK119 by HULC and methylation of histone H3K4 by Set1C are functionally coupled in MTS. Cell-type biases in MTS in these mutants suggested that HULC and Set1C inhibit the use of the SRE3 recombination enhancer in M cells, thus favoring SRE2 and mat2-P. Consistent with this, imbalanced switching in the mutants was traced to compromised association of the directionality factor Swi6 with the recombination enhancers in M cells. Based on their known effects at other chromosomal locations, we speculate that HULC and Set1C control nucleosome mobility and strand invasion near the SRE elements. In addition, we uncovered distinct effects of HULC and Set1C on histone H3K9 methylation and gene silencing, consistent with additional functions in the heterochromatic domain.

Continuity of spermatogenesis in mammals is underpinned by spermatogenic (also called spermatogonial) stem cells (SSCs) that self-renew and differentiate into sperm that pass on genetic information to the next generation. Despite the fundamental role of SSCs, the mechanisms underlying SSC homeostasis are only partly understood. During homeostasis, the stem cell pool remains constant while differentiating cells are continually produced to replenish the lost differentiated cells. One of the outstanding questions here is how self-renewal and differentiation of SSCs are balanced to achieve a constant self-renewing pool. In this review, we shed light on the regulatory mechanism of SSC homeostasis, with focus on the recently proposed mitogen competition model in a facultative (or open) niche microenvironment.

Meiosis is a crucial process for spermatogenesis and oogenesis. Initiation of meiosis coincides with spermatocyte differentiation and is followed by meiotic prophase, a prolonged G2 phase that ensures the completion of numerous meiosis-specific chromosome events. During meiotic prophase, chromosomes are organized into axis-loop structures, which underlie meiosis-specific events such as meiotic recombination and homolog synapsis. In spermatocytes, meiotic prophase is accompanied by robust alterations of gene expression programs and chromatin status for subsequent sperm production. The mechanisms regulating meiotic initiation and subsequent meiotic prophase programs are enigmatic. Recently, we discovered MEIOSIN (Meiosis initiator), a DNA-binding protein that directs the switch from mitosis to meiosis. This review mainly focuses on how MEIOSIN is involved in meiotic initiation and the meiotic prophase program during spermatogenesis. Further, we discuss the downstream genes activated by MEIOSIN, which are crucial for meiotic prophase-specific events, from the viewpoint of chromosome dynamics and the gene expression program.