Madaan, U. | bioRxiv Science

bioRxiv2019

Feedback regulation of BMP signaling by C. elegans cuticle collagens

Cellular responsiveness to environmental cues, including changes in extracellular matrix (ECM), is critical for normal processes such as development and wound healing, but can go awry, as in oncogenesis and fibrosis. One type of molecular pathway allowing this responsiveness is the bone morphogenetic protein (BMP) signaling pathway. Due to their broad and potent functions, BMPs and their signaling pathways are highly regulated at multiple levels. In Caenorhabditis elegans, the BMP ligand DBL-1 is a major regulator of body size. We have previously shown that DBL-1/BMP signaling determines body size through transcriptional regulation of cuticle collagen genes. We have now obtained evidence of feedback regulation of DBL-1/BMP by collagen genes. We analyzed four DBL-1-regulated collagen genes that affect body size. Here we show that inactivation of any one of these cuticle collagen genes reduces DBL-1/BMP signaling, as measured by a Smad activity reporter. Furthermore, we find that depletion of these collagens reduces GFP::DBL-1 fluorescence, and acts unexpectedly at the level of dbl-1 transcription. We therefore conclude that cuticle, a type of ECM, impinges on DBL-1/BMP expression and signaling. In contrast to other characterized examples, however, the feedback regulation of DBL-1/BMP signaling by collagens is likely to be contact-independent, due to the physical separation of the cuticle from DBL-1-expressing cells in the ventral nerve cord. Our results provide an entry point into a novel mechanism of regulation of BMP signaling, with broader implications for mechanical regulation of gene expression in general.

developmental biology↗

bioRxiv2017

Caenorhabditis elegans BMP Transcriptional ProgramImplicates Collagen Genes in Body Size Regulation

Body size is a tightly regulated phenotype in metazoans that is dependent on both intrinsic and extrinsic factors. While signaling pathways such as insulin, Hippo, and myostatin are known to control organ and body size, the downstream effectors that mediate their effects are still poorly understood. In the nematode C. elegans, a Bone Morphogenetic Protein (BMP)-related signaling pathway is the major regulator of growth and body size. DBL-1, the BMP-related ligand, is secreted by neurons and body wall muscle, and acts as a dose-dependent regulator of body size. We investigated the transcriptional network through which the DBL-1/BMP pathway regulates body size and identified cuticle collagen genes as major effectors of growth control. Here we demonstrate that cuticle collagen genes can act as positive regulators (col-41), dose-sensitive regulators (rol-6), and negative regulators (col-141, col-142) of body size. Moreover, we show requirement of DBL-1/BMP signaling for stage-specific expression of cuticle collagen genes. We used chromatin immunoprecipitation followed by high throughput sequencing (ChIP-Seq) and electrophoretic mobility shift assays to show that the Smad signal transducers directly associate with conserved Smad binding elements in regulatory regions of col-141 and col-142, but not of col-41. Hence, cuticle collagen genes are directly and indirectly regulated via the DBL-1/BMP pathway. These results provide the first direct regulatory link between this conserved signaling pathway and the collagen genes that act as its downstream effectors in body size regulation. Since collagen mutations and misregulation are implicated in numerous human genetic disorders and injury sequelae, understanding how collagen gene expression is regulated has broad implications.\n\nAuthor SummaryBody size in humans and other animals is determined by the combined influence of genetic and environmental factors. Failure to regulate growth and body size appropriately can lead to a variety of functional impairments and reduced fitness. Progress has been made in identifying genetic determinants of body size, but these have not often been connected into functional pathways. In the nematode model Caenorhabditis elegans, single gene mutations in the BMP signaling pathway have profound effects on body size. Here we have elucidated the BMP transcriptional network and identified cuticle collagen genes as downstream effectors of body size regulation through the BMP pathway. Collagens play diverse roles in biology; mutations are often associated with rare heritable diseases such as osteogenesis imperfecta and Ehlers-Danlos syndrome. Our work thus connects a conserved signaling pathway with its critical downstream effectors, advancing insight into how body size is specified.

genetics↗