Mitochondrial remodelling is essential for female germ cell differentiation and survival.

Stem cells often possess immature mitochondria with few inner membrane invaginations, which increase as stem cells differentiate. Despite this being a conserved feature across many stem cell types in numerous organisms, how and why mitochondria undergo such remodelling during stem cell differentiation has remained unclear. Here, using Drosophila germline stem cells (GSCs), we show that Complex V drives mitochondrial remodelling during the early stages of GSC differentiation, prior to terminal differentiation. This endows germline mitochondria with the capacity to generate large amounts of ATP required for later egg growth and development. Interestingly, impairing mitochondrial remodelling prior to terminal differentiation results in endoplasmic reticulum (ER) lipid bilayer stress, Protein kinase R-like ER kinase (PERK)-mediated activation of the Integrated Stress Response (ISR) and germ cell death. Taken together, our data suggest that mitochondrial remodelling is an essential and tightly integrated aspect of stem cell differentiation. This work sheds light on the potential impact of mitochondrial dysfunction on stem and germ cell function, highlighting ER lipid bilayer stress as a potential major driver of phenotypes caused by mitochondrial dysfunction.

Mitochondrial DNA quality control in the female germline requires a unique programmed mitophagy.

Mitochondria have their own DNA (mtDNA), which is susceptible to the accumulation of disease-causing mutations. To prevent deleterious mutations from being inherited, the female germline has evolved a conserved quality control mechanism that remains poorly understood. Here, through a large-scale screen, we uncover a unique programmed germline mitophagy (PGM) that is essential for mtDNA quality control. We find that PGM is developmentally triggered as germ cells enter meiosis by inhibition of the target of rapamycin complex 1 (TORC1). We identify a role for the RNA-binding protein Ataxin-2 (Atx2) in coordinating the timing of PGM with meiosis. We show that PGM requires the mitophagy receptor BNIP3, mitochondrial fission and translation factors, and members of the Atg1 complex, but not the mitophagy factors PINK1 and Parkin. Additionally, we report several factors that are critical for germline mtDNA quality control and show that pharmacological manipulation of one of these factors promotes mtDNA quality control.

Plasmalogen loss caused by remodeling deficiency in mitochondria.

Lipid homeostasis is crucial in human health. Barth syndrome (BTHS), a life-threatening disease typically diagnosed with cardiomyopathy and neutropenia, is caused by mutations in the mitochondrial transacylase tafazzin. By high-resolution 31P nuclear magnetic resonance (NMR) with cryoprobe technology, recently we found a dramatic loss of choline plasmalogen in the tafazzin-knockdown (TAZ-KD) mouse heart, besides observing characteristic cardiolipin (CL) alterations in BTHS. In inner mitochondrial membrane where tafazzin locates, CL and diacyl phosphatidylethanolamine are known to be essential via lipid-protein interactions reflecting their cone shape for integrity of respiratory chain supercomplexes and cristae ultrastructure. Here, we investigate the TAZ-KD brain, liver, kidney, and lymphoblast from patients compared with controls. We identified common yet markedly cell type-dependent losses of ethanolamine plasmalogen as the dominant plasmalogen class therein. Tafazzin function thus critically relates to homeostasis of plasmalogen, which in the ethanolamine class has conceivably analogous and more potent molecular functions in mitochondria than diacyl phosphatidylethanolamine. The present discussion of a loss of plasmalogen-protein interaction applies to other diseases with mitochondrial plasmalogen loss and aberrant forms of this organelle, including Alzheimer's disease.

Genome-Wide CRISPR-Cas9 Screens Expose Genetic Vulnerabilities and Mechanisms of Temozolomide Sensitivity in Glioblastoma Stem Cells.

Glioblastoma therapies have remained elusive due to limitations in understanding mechanisms of growth and survival of the tumorigenic population. Using CRISPR-Cas9 approaches in patient-derived GBM stem cells (GSCs) to interrogate function of the coding genome, we identify actionable pathways responsible for growth, which reveal the gene-essential circuitry of GBM stemness and proliferation. In particular, we characterize members of the SOX transcription factor family, SOCS3, USP8, and DOT1L, and protein ufmylation as important for GSC growth. Additionally, we reveal mechanisms of temozolomide resistance that could lead to combination strategies. By reaching beyond static genome analysis of bulk tumors, with a genome-wide functional approach, we reveal genetic dependencies within a broad range of biological processes to provide increased understanding of GBM growth and treatment resistance.