Mutations of the Genomes Uncoupled 4 Gene Cause ROS Accumulation and Repress Expression of Peroxidase Genes in Rice

The Genomes Uncoupled 4 (GUN4) is one of the retrograde signaling genes in Arabidopsis and its orthologs have been identified in oxygenic phototrophic organisms from cyanobacterium to higher plants. GUN4 is involved in tetrapyrrole biosynthesis and its mutation often causes chlorophyll-deficient phenotypes with increased levels of reactive oxygen species (ROS), hence it has been speculated that GUN4 may also play a role in photoprotection. However, the biological mechanism leading to the increased ROS accumulation in gun4 mutants remains largely unknown. In our previous studies, we generated an epi-mutant allele of OsGUN4 (gun4epi), which downregulated its expression to ∼0.5% that of its wild-type (WT), and a complete knockout allele gun4-1 due to abolishment of its translation start site. In the present study, three types of F2 plant derived from a gun4-1/gun4epi cross, i.e., gun4-1/gun4-1, gun4-1/gun4epi and gun4epi/gun4epi were developed and used for further investigation by growing them under photoperiodic condition (16 h/8 h light/dark) with low light (LL, 100 μmol photons m–2 s–1) or high light (HL, 1000 μmol photons m–2 s–1). The expression of OsGUN4 was light responsive and had two peaks in the daytime. gun4-1/gun4-1-F2 seeds showed defective germination and died within 7 days. Significantly higher levels of ROS accumulated in all types of OsGUN4 mutants than in WT plants under both the LL and HL conditions. A comparative RNA-seq analysis of WT variety LTB and its gun4epi mutant HYB led to the identification of eight peroxidase (PRX)-encoding genes that were significantly downregulated in HYB. The transcription of these eight PRX genes was restored in transgenic HYB protoplasts overexpressing OsGUN4, while their expression was repressed in LTB protoplasts transformed with an OsGUN4 silencing vector. We conclude that OsGUN4 is indispensable for rice, its expression is light- and oxidative-stress responsive, and it plays a role in ROS accumulation via its involvement in the transcriptional regulation of PRX genes.

Maintenance of complex I and its super-complexes by NDUF-11 is essential for mitochondrial structure, function and health

Mitochondrial super-complexes form around a conserved core of monomeric complex I and dimeric complex III; wherein subunit NDUFA11, of the former, is conspicuously situated at the interface. We identified B0491.5 (NDUF-11) as the C. elegans homologue, of which animals homozygous for a CRISPR-Cas9 generated knockout allele arrested at the L2 development stage. Reducing (but not eliminating) expression by RNAi allowed development to adulthood, enabling characterisation of the consequences: destabilisation of complex I and its super-complexes, and perturbation of respiratory function. The loss of NADH-dehydrogenase activity is compensated by enhanced complex II activity, with the potential for detrimental ROS-production. Electron cryo-tomography highlight aberrant cristae morphology and inter-membrane-space widening and cristae-junctions. The requirement of NDUF-11 for balanced respiration, mitochondrial morphology and development presumably arises due to its involvement in complex I/ super-complex maintenance. This highlights the importance of respiratory complex integrity for health and the potential of its perturbation for mitochondrial disease.

Zebrafish heme oxygenase 1a is necessary for normal development and macrophage migration

Heme oxygenase function is highly conserved between vertebrates where it plays important roles in normal embryonic development and controls oxidative stress. Expression of the zebrafish heme oxygenase 1 genes are known to be responsive to oxidative stress suggesting a conserved physiological function. Here we generate a knockout allele of zebrafish hmox1a and characterize the effects of hmox1a and hmox1b loss on embryonic development. We find that loss of hmox1a or hmox1b causes developmental defects in only a minority of embryos, in contrast to Hmox1 gene deletions in mice that causes loss of most embryos. Using a tail wound inflammation assay we find a conserved role for hmox1a, but not hmox1b, in normal macrophage migration to the wound site. Together our results indicate zebrafish hmox1a is the most important heme oxygenase 1 gene in zebrafish.

Generation and identification of a conditional knockout allele for the PSMD11 gene in mice

Background Our previous study have shown that the PSMD11 protein was an important survival factor for cancer cells except for its key role in regulation of assembly and activity of the 26S proteasome. To further investigate the role of PSMD11 in carcinogenesis, we constructed a conditional exon 5 floxed allele of PSMD11 (PSMD11flx) in mice. Results It was found that homozygous PSMD11 flx/flx mice showed normal and exhibited a normal life span and fertility, and showed roughly equivalent expression of PSMD11 in various tissues, suggesting that the floxed allele maintained the wild-type function. Cre recombinase could induce efficient knockout of the floxed PSMD11 allele both in vitro and in vivo. Mice with constitutive single allele deletion of PSMD11 derived from intercrossing between PSMD11flx/flx and CMV-Cre mice were all viable and fertile, and showed apparent growth retardation, suggesting that PSMD11 played a significant role in the development of mice pre- or postnatally. No whole-body PSMD11 deficient embryos (PSMD11−/−) were identified in E7.5–8.5 embryos in uteros, indicating that double allele knockout of PSMD11 leads to early embryonic lethality. To avoid embryonic lethality produced by whole-body PSMD11 deletion, we further developed conditional PSMD11 global knockout mice with genotype Flp;FSF-R26CAG − CreERT2/+; PSMD11flx/flx, and demonstrated that PSMD11 could be depleted in a temporal and tissue-specific manner. Meanwhile, it was found that depletion of PSMD11 could induce massive apoptosis in MEFs. Conclusions In summary, our data demonstrated that we have successfully generated a conditional knockout allele of PSMD11 in mice, and found that PSMD11 played a key role in early and postnatal development in mice, the PSMD11 flx/flx mice will be an invaluable tool to explore the functions of PSMD11 in development and diseases.

Depletion of SMC5/6 sensitizes male germ cells to DNA damage

The structural maintenance of chromosomes complex SMC5/6 is thought to be essential for DNA repair and chromosome segregation during mitosis and meiosis. To determine the requirements of the SMC5/6 complex during mouse spermatogenesis we combined a conditional knockout allele for Smc5, with four germ cell–specific Cre-recombinase transgenes, Ddx4-Cre, Stra8-Cre, Spo11-Cre, and Hspa2-Cre, to mutate Smc5 in spermatogonia, in spermatocytes before meiotic entry, during early meiotic stages, and during midmeiotic stages, respectively. Conditional mutation of Smc5 resulted in destabilization of the SMC5/6 complex. Despite this, we observed only mild defects in spermatogenesis. Mutation of Smc5 mediated by Ddx4-Cre and Stra8-Cre resulted in partial loss of preleptotene spermatocytes; however, spermatogenesis progresses and mice are fertile. Mutation of Smc5 via Spo11-Cre or Hspa2-Cre did not result in detectable defects of spermatogenesis. Upon exposure to gamma irradiation or etoposide treatment, each conditional Smc5 mutant demonstrated an increase in the number of enlarged round spermatids with multiple acrosomes and supernumerary chromosome content. We propose that the SMC5/6 complex is not acutely required for premeiotic DNA replication and meiotic progression during mouse spermatogenesis; however, when germ cells are challenged by exogenous DNA damage, the SMC5/6 complex ensures genome integrity, and thus, fertility.

Multiple neurons encode CrebB dependent appetitive long-term memory in the mushroom body circuit

Lasting changes in gene expression are critical for the formation of long-term memories (LTMs), depending on the conserved CrebB transcriptional activator. While requirement of distinct neurons in defined circuits for different learning and memory phases have been studied in detail, only little is known regarding the gene regulatory changes that occur within these neurons. We here use the fruit fly as powerful model system to study the neural circuits of CrebB-dependent appetitive olfactory LTM. We edited the CrebB locus to create a GFP-tagged CrebB conditional knockout allele, allowing us to generate mutant, post-mitotic neurons with high spatial and temporal precision. Investigating CrebB-dependence within the mushroom body (MB) circuit we show that MB α/β and α’/β’ neurons as well as MBON α3, but not in dopaminergic neurons require CrebB for LTM. Thus, transcriptional memory traces occur in different neurons within the same neural circuit.

Onecut-2 knockout mice fail to thrive during early postnatal period and have altered patterns of gene expression in small intestine

Ablation of the mouse genes for Onecut-2 and Onecut-3 was reported previously, but characterization of the resulting knockout mice was focused on in utero development, principally embryonic development of liver and pancreas. Here we examined postnatal development of these Onecut knockout mice, especially the critical period before weaning. Onecut-3 knockout mice develop normally during this period. However, Onecut-2 knockout mice fail to thrive, lagging behind their littermates in size and weight. By postnatal day (d)19, they are consistently 25–30% smaller. Onecut-2 knockout mice also have a much higher level of mortality before weaning, with only ∼70% survival. Interestingly, Onecut-2 knockout mice that are heterozygous for the Onecut-3 knockout allele are diminished even further in their ability to thrive. They are ∼50–60% as large as their normal-sized littermates at d19, and less than half of these mice survive to weaning. As reported previously, the Onecut-2/Onecut-3 double knockout is a perinatal lethal. Microarray technology was used to determine the effect of Onecut-2 ablation on gene expression in duodenum, whose epithelium has among the highest levels of Onecut-2. A subset of intestinally expressed genes showed dramatically altered patterns of expression. Many of these genes encode proteins associated with the epithelial membrane, including many involved in transport and metabolism. Previously, we reported that Onecut-2 was critical to temporal regulation of the adenosine deaminase gene in duodenum. Many of the genes with altered patterns of expression in Onecut-2 knockout mouse duodenum displayed changes in the timing of gene expression.