RNA exosome ribonuclease DIS3 degrades Pou6f1 to promote mouse pre-implantation cell differentiation

Mammalian development is precisely controlled by cell differentiation. Identifying new regulators and investigating their interactions provide insight into genetic networks defining pre-implantation development. We established a knockout mouse model of Dis3, an exosome associated ribonuclease. Homozygous Dis3 null embryos arrest at the morula stage of development. Using single-embryo RNA sequencing (RNA-seq), we observed persistence of Pou6f1 mRNA in homozygous null Dis3 embryos and that the cognate protein represses transcription of Nanog and Cdx2. The resultant defects in cell differentiation disrupt the morula-to-blastocyst transition and are embryonic lethal. Microinjection of Dis3 mRNA into zygotes rescues the phenotype. Point mutations of Dis3 ribonuclease in individual blastomeres prevents their incorporation into embryos. To overcome the paucity of embryos, we derived homozygous Dis3 null mouse embryonic stem cells to identify additional gene targets of POU6F1. Our findings delineate a regulatory pathway of DIS3-POU6F1 in pre-implantation mammalian embryogenesis.

Structural insight into DNA recognition by bacterial transcriptional regulators of the SorC/DeoR family

The SorC/DeoR family is a large family of bacterial transcription regulators that are involved in the control of carbohydrate metabolism and quorum sensing. To understand the structural basis of DNA recognition, structural studies of two functionally characterized SorC/DeoR family members from Bacillus subtilis were performed: the deoxyribonucleoside regulator bsDeoR and the central glycolytic genes regulator bsCggR. Each selected protein represents one of the subgroups that are recognized within the family. Crystal structures were determined of the N-terminal DNA-binding domains of bsDeoR and bsCggR in complex with DNA duplexes representing the minimal operator sequence at resolutions of 2.3 and 2.1 Å, respectively. While bsDeoR_DBD contains a homeodomain-like HTH-type domain, bsCggR_DBD contains a winged helix-turn-helix-type motif. Both proteins form C2-symmetric dimers that recognize two consecutive major grooves, and the protein-DNA interactions have been analyzed in detail. The crystal structures were used to model the interactions of the proteins with the full DNA operators, and a common mode of DNA recognition is proposed that is most likely to be shared by other members of the SorC/DeoR family.

Bacterial Transcription Factors: Regulation by Pick "N" Mix

Transcription in most bacteria is tightly regulated in order to facilitate bacterial adaptation to different environments, and transcription factors play a key role in this. Here we give a brief overview of the essential features of bacterial transcription factors and how they affect transcript initiation at target promoters. We focus on complex promoters that are regulated by combinations of activators and repressors, combinations of repressors only, or combinations of activators. At some promoters, transcript initiation is regulated by nucleoid-associated proteins, which often work together with transcription factors. We argue that the distinction between nucleoid-associated proteins and transcription factors is blurred and that they likely share common origins.

Crystallization and preliminary X-ray analysis of BigR, a transcription repressor from Xylella fastidiosa involved in biofilm formation

BigR (biofilm growth-associated repressor) is a novel repressor protein that regulates the transcription of an operon implicated in biofilm growth in both Xylella fastidiosa and Agrobacterium tumefaciens. This protein binds to a palindromic TA-rich element located in the promoter of the BigR operon and strongly represses transcription of the operon. BigR contains a helix-turn-helix (HTH) domain that is found in some members of the ArsR/SmtB family of metal sensors, which control metal resistance in bacteria. Although functional studies have suggested that BigR does not act as a metal sensor, the presence of two cysteines and a methionine in its primary structure raised the possibility of BigR being a metal-ligand protein. In order to gain new insights into the protein structure and its possible interaction with a metal ion or effector ligand, BigR from X. fastidiosa was crystallized in native and selenomethionine (SeMet) labelled forms using the hanging-drop vapour-diffusion method. X-ray diffraction data were collected from native and SeMet crystals to resolutions of 1.95 and 2.2 A, respectively. Both crystals belong to space group P321 and contain one molecule per asymmetric unit.