Sideroflexin 3 is an α-synuclein-dependent mitochondrial protein that regulates synaptic morphology.

α-Synuclein plays a central role in Parkinson's disease, where it contributes to the vulnerability of synapses to degeneration. However, the downstream mechanisms through which α-synuclein controls synaptic stability and degeneration are not fully understood. Here, comparative proteomics on synapses isolated from α-synuclein-/- mouse brain identified mitochondrial proteins as primary targets of α-synuclein, revealing 37 mitochondrial proteins not previously linked to α-synuclein or neurodegeneration pathways. Of these, sideroflexin 3 (SFXN3) was found to be a mitochondrial protein localized to the inner mitochondrial membrane. Loss of SFXN3 did not disturb mitochondrial electron transport chain function in mouse synapses, suggesting that its function in mitochondria is likely to be independent of canonical bioenergetic pathways. In contrast, experimental manipulation of SFXN3 levels disrupted synaptic morphology at the Drosophila neuromuscular junction. These results provide novel insights into α-synuclein-dependent pathways, highlighting an important influence on mitochondrial proteins at the synapse, including SFXN3. We also identify SFXN3 as a new mitochondrial protein capable of regulating synaptic morphology in vivo.

Evolutionary origin of vertebrate OCT4/POU5 functions in supporting pluripotency.

The support of pluripotent cells over time is an essential feature of development. In eutherian embryos, pluripotency is maintained from naïve states in peri-implantation to primed pluripotency at gastrulation. To understand how these states emerged, we reconstruct the evolutionary trajectory of the Pou5 gene family, which contains the central pluripotency factor OCT4. By coupling evolutionary sequence analysis with functional studies in mouse embryonic stem cells, we find that the ability of POU5 proteins to support pluripotency originated in the gnathostome lineage, prior to the generation of two paralogues, Pou5f1 and Pou5f3 via gene duplication. In osteichthyans, retaining both genes, the paralogues differ in their support of naïve and primed pluripotency. The specialization of these duplicates enables the diversification of function in self-renewal and differentiation. By integrating sequence evolution, cell phenotypes, developmental contexts and structural modelling, we pinpoint OCT4 regions sufficient for naïve pluripotency and describe their adaptation over evolutionary time.

Modeling Parkinson's disease with induced pluripotent stem cells harboring α-synuclein mutations.

Parkinson's disease (PD) is a common neurodegenerative condition affecting more than 8 million people worldwide. Although, the majority of PD cases are sporadic in nature, there are a growing number of monogenic mutations identified to cause PD in a highly penetrant manner. Many of these familial mutations give rise to a condition that is clinically and neuropathologically similar, if not identical, to sporadic PD. Mutations in genes such as SNCA cause PD in an autosomal dominant manner and patients have motor and non-motor symptoms that are typical for sporadic PD. With the advent of reprogramming technology it is now possible to capture these mutations in induced pluripotent stem cells (iPSCs) to establish models of PD in a dish. There are multiple neuronal subtypes affected in PD including the midbrain dopaminergic (mDA) neurons of the substantia nigra. Robust neuronal differentiation into mDA or other relevant neural cell types are critical to accurately model the disease and ensure the findings are relevant to understanding the disease process. Another challenge for establishing accurate models of PD is being met by the generation of isogenic control iPSC lines with precise correction of mutations using advanced gene editing technology. The contributions of ageing and environmental factors present further challenges to this field, but significant progress is being made in these areas to establish highly relevant and robust models of PD. These human neuronal models, used in conjunction with other model systems, will vastly improve our understanding of the early stages of the PD, which will be key to identifying disease-modifying and preventative treatments.

A conserved Oct4/POUV-dependent network links adhesion and migration to progenitor maintenance.

BACKGROUND: The class V POU domain transcription factor Oct4 (Pou5f1) is a pivotal regulator of embryonic stem cell (ESC) self-renewal and reprogramming of somatic cells to induced pluripotent stem (iPS) cells. Oct4 is also an important evolutionarily conserved regulator of progenitor cell differentiation during embryonic development. RESULTS: Here we examine the function of Oct4 homologs in Xenopus embryos and compare this to the role of Oct4 in maintaining mammalian embryo-derived stem cells. Based on a combination of expression profiling of Oct4/POUV-depleted Xenopus embryos and in silico analysis of existing mammalian Oct4 target data sets, we defined a set of evolutionary-conserved Oct4/POUV targets. Most of these targets were regulators of cell adhesion. This is consistent with Oct4/POUV phenotypes observed in the adherens junctions in Xenopus ectoderm, mouse embryonic, and epiblast stem cells. A number of these targets could rescue both Oct4/POUV phenotypes in cellular adhesion and multipotent progenitor cell maintenance, whereas expression of cadherins on their own could only transiently support adhesion and block differentiation in both ESC and Xenopus embryos. CONCLUSIONS: Currently, the list of Oct4 transcriptional targets contains thousands of genes. Using evolutionary conservation, we identified a core set of functionally relevant factors that linked the maintenance of adhesion to Oct4/POUV. We found that the regulation of adhesion by the Oct4/POUV network occurred at both transcriptional and posttranslational levels and was required for pluripotency.

Transcriptional activation by Oct4 is sufficient for the maintenance and induction of pluripotency.

Oct4 is an essential regulator of pluripotency in vivo and in vitro in embryonic stem cells, as well as a key mediator of the reprogramming of somatic cells into induced pluripotent stem cells. It is not known whether activation and/or repression of specific genes by Oct4 is relevant to these functions. Here, we show that fusion proteins containing the coding sequence of Oct4 or Xlpou91 (the Xenopus homolog of Oct4) fused to activating regions, but not those fused to repressing regions, behave as Oct4, suppressing differentiation and promoting maintenance of undifferentiated phenotypes in vivo and in vitro. An Oct4 activation domain fusion supported embryonic stem cell self-renewal in vitro at lower concentrations than that required for Oct4 while alleviating the ordinary requirement for the cytokine LIF. At still lower levels of the fusion, LIF dependence was restored. We conclude that the necessary and sufficient function of Oct4 in promoting pluripotency is to activate specific target genes.