Postnatal persistence of hippocampal Cajal-Retzius cells has a crucial role in the establishment of the hippocampal circuit.

Cajal-Retzius (CR) cells are a transient neuron type that populate the postnatal hippocampus. To understand how the persistence of CR cells influences the maturation of hippocampal circuits, we combined a specific transgenic mouse line with viral vector injection to selectively ablate CR cells from the postnatal hippocampus. We observed layer-specific changes in the dendritic complexity and spine density of CA1 pyramidal cells. In addition, transcriptomic analysis highlighted significant changes in the expression of synapse-related genes across development. Finally, we were able to identify significant changes in the expression levels of latrophilin 2, a postsynaptic guidance molecule known for its role in the entorhinal-hippocampal connectivity. These findings were supported by changes in the synaptic proteomic content in CA1 stratum lacunosum-moleculare. Our results reveal a crucial role for CR cells in the establishment of the hippocampal network.

Dynamic features of human mitochondrial DNA maintenance and transcription.

Mitochondria are the primary sites for cellular energy production and are required for many essential cellular processes. Mitochondrial DNA (mtDNA) is a 16.6 kb circular DNA molecule that encodes only 13 gene products of the approximately 90 different proteins of the respiratory chain complexes and an estimated 1,200 mitochondrial proteins. MtDNA is, however, crucial for organismal development, normal function, and survival. MtDNA maintenance requires mitochondrially targeted nuclear DNA repair enzymes, a mtDNA replisome that is unique to mitochondria, and systems that control mitochondrial morphology and quality control. Here, we provide an overview of the current literature on mtDNA repair and transcription machineries and discuss how dynamic functional interactions between the components of these systems regulate mtDNA maintenance and transcription. A profound understanding of the molecular mechanisms that control mtDNA maintenance and transcription is important as loss of mtDNA integrity is implicated in normal process of aging, inflammation, and the etiology and pathogenesis of a number of diseases.

Loss of Mediator complex subunit 13 (MED13) promotes resistance to alkylation through cyclin D1 upregulation.

Alkylating drugs are among the most often used chemotherapeutics. While cancer cells frequently develop resistance to alkylation treatments, detailed understanding of mechanisms that lead to the resistance is limited. Here, by using genome-wide CRISPR-Cas9 based screen, we identify transcriptional Mediator complex subunit 13 (MED13) as a novel modulator of alkylation response. The alkylation exposure causes significant MED13 downregulation, while complete loss of MED13 results in reduced apoptosis and resistance to alkylating agents. Transcriptome analysis identified cyclin D1 (CCND1) as one of the highly overexpressed genes in MED13 knock-out (KO) cells, characterized by shorter G1 phase. MED13 is able to bind to CCND1 regulatory elements thus influencing the expression. The resistance of MED13 KO cells is directly dependent on the cyclin D1 overexpression, and its down-regulation is sufficient to re-sensitize the cells to alkylating agents. We further demonstrate the therapeutic potential of MED13-mediated response, by applying combinatory treatment with CDK8/19 inhibitor Senexin A. Importantly, the treatment with Senexin A stabilizes MED13, and in combination with alkylating agents significantly reduces viability of cancer cells. In summary, our findings identify novel alkylation stress response mechanism dependent on MED13 and cyclin D1 that can serve as basis for development of innovative therapeutic strategies.

Enhanced amphiphilic profile of a short ß-stranded peptide improves its antimicrobial activity.

SB056 is a novel semi-synthetic antimicrobial peptide with a dimeric dendrimer scaffold. Active against both Gram-negative and -positive bacteria, its mechanism has been attributed to a disruption of bacterial membranes. The branched peptide was shown to assume a ß-stranded conformation in a lipidic environment. Here, we report on a rational modification of the original, empirically derived linear peptide sequence [WKKIRVRLSA-NH2, SB056-lin]. We interchanged the first two residues [KWKIRVRLSA-NH2, ß-SB056-lin] to enhance the amphipathic profile, in the hope that a more regular ß-strand would lead to a better antimicrobial performance. MIC values confirmed that an enhanced amphiphilic profile indeed significantly increases activity against both Gram-positive and -negative strains. The membrane binding affinity of both peptides, measured by tryptophan fluorescence, increased with an increasing ratio of negatively charged/zwitterionic lipids. Remarkably, ß-SB056-lin showed considerable binding even to purely zwitterionic membranes, unlike the original sequence, indicating that besides electrostatic attraction also the amphipathicity of the peptide structure plays a fundamental role in binding, by stabilizing the bound state. Synchrotron radiation circular dichroism and solid-state 19F-NMR were used to characterize and compare the conformation and mobility of the membrane bound peptides. Both SB056-lin and ß-SB056-lin adopt a ß-stranded conformation upon binding POPC vesicles, but the former maintains an intrinsic structural disorder that also affects its aggregation tendency. Upon introducing some anionic POPG into the POPC matrix, the sequence-optimized ß-SB056-lin forms well-ordered ß-strands once electro-neutrality is approached, and it aggregates into more extended ß-sheets as the concentration of anionic lipids in the bilayer is raised. The enhanced antimicrobial activity of the analogue correlates with the formation of these extended ß-sheets, which also leads to a dramatic alteration of membrane integrity as shown by 31P-NMR. These findings are generally relevant for the design and optimization of other membrane-active antimicrobial peptides that can fold into amphipathic ß-strands.