Identifying cell non-autonomous factors that coordinate organism-wide growth:

What are the signals that are communicated between different cells, organs and systems of an organism that provide a checkpoint for organismal growth?

Despite our understanding of the fundamental molecular basis of tissue growth and organogenesis, we know very little about how growth is coordinated across multiple systems of an organism. First, we are identifying regulators of cell non-autonomous growth arrest in C. elegans by intensive forward genetic screens in strains that produce both wild-type and homozygous RP& rDNA null cells in precise lineages. Second, to understand tissue specific contributions to organism-wide growth, we are currently optimizing a system that will reversibly block new ribosome synthesis in a tissue and stage-specific way. Overall, this study will shed light onto the cell non-autonomous pathways that regulate organism-wide growth coordination.

1- Characterization of cell non-autonomous factors that coordinate organism-wide growth control

Our goal here is characterize the molecular mechanisms that enable communication between cells to coordinate organismal growth. We will combine with forward genetics screens in RP null/wild- type mosaic individuals with a systems level approach to identify cell non-autonomous regulators of body-wide growth. Combining classical and novel genetics with cutting edge systems analyses tools in C. elegans is enabling us to elucidate the conserved genetic factors that are communicated between different cells, organs and systems to coordinate growth. To identify regulators of cell non-autonomous growth arrest in C. elegans in an unbiased fashion, we are performing targeted and forward genetics with strains that produce mosaic larvae. We are identifying mutations that suppress the cell non-autonomous checkpoint. We monitor lineage-specific characteristics of the mosaic larvae with RP null and wild-type cells using lineage specific patterns labeled with a series
of fluorescent markers as illustrated.

These analyses will reveal novel factors that facilitate communication between cells for coordinating overall organism growth. Since ribosome components and key signaling pathway families are highly conserved between C. elegans and humans, we expect the identified pathways to be informative for humans

2- Delineating the tissue specific contributions to coordination of organism-wide growth

Our goal is to determine the tissue specific contributions to systems level communication for coordination of organismal growth. There is preliminary evidence that tissue specific knockdown of ribosomal proteins could lead to whole body growth arrest and yet we lack a genetic handle to study its mechanism. Our preliminary data established the presence of a cell-non-autonomous signal that provides a checkpoint for new ribosome synthesis and inhibits postembryonic development. However, it is unclear whether the lack of ribosome synthesis in a particular tissue can drive the observed growth effect. To test this hypothesis, we are currently optimizing a system to reversibly block new ribosome synthesis in a tissue and stage-specific way as illustrated below. Specifically, we are using the auxin-inducible degradation system (AID) as a tool to reversibly and tissue-specifically deplete ribosome components. AID system takes advantage of integration of a short degron tag fused the target protein.

Once our studies are completed, we expect to have a roadmap of genetic factors that coordinate growth in different organs and systems of an animal body.