Asymmetric mitochondrial inheritance: Charting mechanism(s) and function(s) during animal development

The ability of cells to divide asymmetrically and generate daughter cells that adopt different fates is fundamentally important to life. However, the mechanisms that enable divergence of daughter cell fates remain incompletely understood and have been challenging to study in intact living animals. In our work, we use the nematode Caenorhabditis elegans, which is exceptionally well suited for studies of developmental phenomena, including asymmetric cell divisions, and is excellent for imaging-based and genetic approaches. In the past funding period, we developed methodology that enabled us to study the partitioning of mitochondria during asymmetric cell divisions that generate a cell, whose fate it is to die through apoptosis (referred to as ‘unwanted’ cells). Specifically, we discovered that during these ‘life/death’ decisions, unwanted cells inherit fewer mitochondria and the mitochondria they inherit are smaller and more spherical. In addition, we found that there is a correlation between mitochondrial density in unwanted cells and the time it takes these cells to die. Specifically, we found that daughter cells that inherit more mitochondria take longer to die and, in some cases, fail to die. With this, we have uncovered a new intrinsic mechanism required for cell fate divergence in C. elegans. In the current application, we propose to capitalize on our findings and to address the following questions: Aim 1. How do unwanted cells inherit fewer and more spherical mitochondria? We have preliminary evidence that it involves localized mitochondrial fission and targeted mitochondrial transport, and we will explore this using imaging-based approaches, endogenously-tagged proteins and targeted genetic manipulations. Aim 2. How do mitochondria antagonize apoptosis in unwanted cells? Using synthetic tools, we will increase mitochondrial density to test whether this is sufficient to antagonize apoptosis. And we will use imaging, endogenously-tagged proteins, sensors and targeted genetic manipulations to identify candidate mitochondrial proteins and attributes with anti-apoptotic function. Aim 3. What additional factors are required for asymmetric mitochondrial inheritance? We will use an unbiased genetic approach to identify additional processes with a role in asymmetric mitochondrial inheritance in the context of life/death decisions. Aim 4. Is asymmetric mitochondrial inheritance a general feature of asymmetric cell divisions in C. elegans? To answer this, we will study mitochondrial inheritance during the asymmetric stem-like divisions of the epidermal seam cells, using imaging-based methodology that we developed. The proposed work will inform us of a novel internal mechanism of cell fate divergence, a process of particular importance to developmental and stem cell biology. It will also increase our understanding of the partitioning of cytoplasmic organelles, which is of general interest to cell biologists. Mitochondria have emerged as critical determinants of apoptosis and aging; however, much remains unclear about their impact on cell fate, which we will address at an unprecedented level of rigour and spatiotemporal resolution. Therefore, researchers working in the areas of mitochondria, apoptosis and aging will benefit from our results. Finally, the C. elegans community will benefit from an increased understanding of life/death decisions, a key aspect of C. elegans development, and from methodology and tools generated as part of the proposed work. The proposed work addresses a fundamental question in biology i.e. asymmetric mitochondrial inheritance in the context of cell fate divergence and can be considered creative, curiosity-driven frontier bioscience. Therefore, it is highly relevant to the BBSRC long-term research and innovation priorities.