mTORC1/AMPK responses define a core gene set for developmental cell fate switching

Cells respond to nutrient availability through signaling networks that control growth and development. mTORC1 and AMPK are central regulators of these processes, but their downstream transcriptional effects remain poorly defined. Prior research has shown that mTORC1 promotes growth while AMPK activates under starvation. However, the specific genes required for developmental transitions remain unclear. Dictyostelium offers a unique model for studying these transitions due to its well-characterized life cycle. While many genes change with nutrient removal, not all are essential for development. This gap motivated a focused search for a core gene set involved in cell fate switching. The study aimed to distinguish between genes that respond to nutrient loss and those that directly regulate developmental decisions. The challenge lies in isolating the minimal gene set that drives development without relying on nutrient withdrawal. This work builds on prior knowledge of mTORC1 and AMPK but introduces a novel approach to identify developmentally essential genes.

The study aimed to identify a core gene set that regulates developmental fate switching in Dictyostelium. The specific problem addressed is the difficulty in distinguishing between genes that respond to nutrient loss and those that directly control developmental decisions. The motivation stems from the observation that many genes change with nutrient removal, yet only a subset is essential for development. The researchers proposed that manipulating mTORC1 activity alone could reveal these essential genes without requiring nutrient withdrawal. This approach allows for a clearer understanding of the transcriptional networks involved in developmental induction. The study sought to determine whether mTORC1 and AMPK activities could drive developmental fate changes independently of nutrient status. By focusing on gene expression changes under controlled conditions, the researchers aimed to identify a minimal set of genes required for development. This work provides a framework for understanding how signaling pathways regulate cell fate decisions in response to metabolic cues.

The researchers used Dictyostelium as a model system to study mTORC1 and AMPK signaling during growth and development. They manipulated mTORC1 activity using rapamycin to induce a growth-to-development switch without nutrient withdrawal. Gene expression profiles were analyzed under conditions of active mTORC1 and AMPK to identify transcriptional changes. The study compared gene expression in cells undergoing development triggered by mTORC1 inactivation versus natural nutrient withdrawal. RNA sequencing was used to measure gene expression changes under different conditions. The researchers focused on genes that changed expression in response to rapamycin treatment but not to nutrient removal. They identified two distinct gene sets: one involved in growth processes and another in developmental signaling. Mutation analysis was performed on selected genes to assess their role in developmental regulation. This approach allowed the researchers to isolate a core gene set essential for developmental induction.

The study found that mTORC1 and AMPK exhibit reciprocal regulation during growth and development in Dictyostelium. Rapamycin treatment, which inhibits mTORC1, induced a growth-to-development switch even in nutrient-rich conditions. Gene expression analysis revealed that approximately 1000 genes were downregulated during this switch. These genes are associated with ribosome biogenesis, protein synthesis, and cell cycle processes. Conversely, about 500 genes were upregulated by rapamycin treatment, forming a network linked to developmental induction. Of these, ~135 genes intersect with the cAMP/PKA signaling pathway. Mutation analyses of five of these genes suggested a novel class of developmentally essential genes. These findings indicate that manipulating mTORC1 activity alone is sufficient to drive developmental fate changes. The results show that developmental induction does not require the full set of starvation-regulated genes. Instead, a smaller subset of genes is sufficient to initiate the developmental program.

The authors concluded that mTORC1 and AMPK activities can drive developmental fate switching in Dictyostelium without nutrient withdrawal. Their findings suggest that a core gene set, rather than the full set of starvation-regulated genes, is essential for developmental induction. The study shows that manipulating mTORC1 activity alone is sufficient to trigger development. The researchers propose that the upregulated genes identified in this study form a signaling network essential for developmental processes. These genes intersect with the cAMP/PKA pathway, which is already known to regulate development in Dictyostelium. Mutation analyses of five genes suggest a novel class of developmentally essential genes. The results indicate that developmental fate decisions can be regulated independently of nutrient status. The study provides a framework for identifying transcriptional networks involved in early development.