Biology subjects

Kaplan, R. E. W.

Publications and source records attributed to Kaplan, R. E. W..

5 recordsLinked to original sources

bioRxiv2018

Developmental fidelity imposed by the RGL-1 balanced switch mediating opposing signals

The six C. elegans vulval precursor cells (VPCs) are induced to form the 30-30-20-{Gamma}-20-3{degrees} pattern of cell fates with high fidelity. In response to EGF signal, the LET-60/Ras-LIN-45/Raf-MEK-2/MEK-MPK-1/ERK canonical MAP kinase cascade is necessary to induce 1{degrees} fate and synthesis of DSL ligands. In turn, LIN-12/Notch signal is necessary to induce neighboring cells to become 2{degrees}. We previously showed that, in response to lower dose of EGF signal, the modulatory LET-60/Ras-RGL-1/RalGEF-RAL-1/Ral signal promotes 2{degrees} fate in support of LIN-12. In this study we identify two key differences between RGL-1 and RAL-1 functions. First, deletion of RGL-1 confers no overt developmental defects, while previous studies showed RAL-1 to be essential for viability and fertility. From this observation we hypothesize that the developmentally essential functions of RAL-1 are independent of upstream activation. Second, RGL-1 plays opposing and genetically separable roles in VPC fate patterning. RGL-1 promotes 2{degrees} fate via canonical GEF-dependent activation of RAL-1 and 1{degrees} fate via a non-canonical GEF-independent activity. Our genetic epistasis experiments are consistent with RGL-1 functioning in the modulatory 1{degrees}-promoting AGE-1/PI3-Kinase-PDK-1-AKT-1 cascade. Additionally, animals without RGL-1 experience 15-fold higher rates of VPC patterning errors compared to the wild type. Yet VPC patterning in RGL-1 deletion mutants is not more sensitive to environmental perturbations. We propose that RGL-1 functions as a \"Balanced Switch\" that orchestrates opposing 1{degrees}- and 2{degrees}-promoting modulatory cascades to decrease inappropriate fate decisions. We speculate that such switches are broadly conserved but mostly masked by paralog redundancy or essential genes.

genetics↗

bioRxiv2018

Ral signals through a MAP4 Kinase-p38 MAP kinase cascade in C. elegans cell fate patterning.

C. elegans vulval precursor cell (VPC) fates are patterned by an EGF gradient. High dose EGF induces 1{degrees} VPC fate, while lower dose EGF contributes to 2{degrees} fate in support of LIN-12/Notch. We previously showed that the EGF 2{degrees}-promoting signal is mediated by LET-60/Ras switching effectors, from the canonical Raf-MEK-ERK MAP kinase cascade that promotes 1{degrees} fate to the non-canonical RalGEF-Ral that promotes 2{degrees} fate. Of oncogenic Ras effectors, RalGEF-Ral is by far the least well-understood. We use genetic analysis to identify an effector cascade downstream of C. elegans RAL-1/Ral, starting with an established Ral binding partner, Exo84 of the exocyst complex. Additionally, RAL-1 signals through GCK-2, a CNH domain-containing MAP4 kinase, and PMK-1/p38 MAP kinase cascade to promote 2{degrees} fate. Our study delineates a Ral-dependent developmental signaling cascade in vivo, thus providing the mechanism by which lower EGF dose is transduced.

developmental biology↗

bioRxiv2018

Intergenerational effects of dietary restriction on insulin/IGF signaling and reproductive development

The roundworm C. elegans transiently arrests larval development to survive extended starvation (1), but such early-life starvation reduces reproductive success (2, 3). Maternal dietary restriction (DR) buffers progeny from starvation, increasing reproductive success (4). It is unknown why early-life starvation decreases reproductive success and how maternal diet modifies this process. We show here that extended starvation in first-stage (L1) larvae followed by unrestricted feeding results in a variety of abnormalities in the reproductive system, including glp-1/Notch-sensitive germ-cell tumors and uterine masses that express neuronal and epidermal markers. We found that maternal DR reduces the penetrance of starvation-induced abnormalities, including tumors. Furthermore, we show that maternal DR reduces insulin/IGF signaling (IIS) in progeny, and that daf-16/FoxO and skn-1/Nrf, transcriptional effectors of IIS, are required in progeny for maternal DR to suppress abnormalities. daf-16/FoxO activity in somatic tissues is sufficient to suppress starvation-induced abnormalities, suggesting cell-nonautonomous regulation of reproductive system development. This work reveals complex inter- and intra-generational effects of nutrient availability mediated by IIS with consequences on developmental integrity and reproductive success.\n\nOne Sentence SummaryIntergenerational effects of diet on IIS

developmental biology↗

bioRxiv2018

Pervasive positive and negative feedback regulation of insulin like signaling in Caenorhabditis elegans

The C. elegans insulin-like signaling network supports homeostasis and developmental plasticity. The genome encodes 40 insulin-like peptides and one receptor. Feedback regulation has been reported, but the extent of feedback and its effect on signaling dynamics during a state transition has not been determined. We measured mRNA expression for each insulin-like peptide, the receptor daf-2, components of the PI3K pathway, and its transcriptional effectors daf-16/FoxO and skn-1/Nrf at high temporal resolution during transition from a starved, quiescent state to a fed, growing state in wild type and mutants affecting daf-2/InsR and daf-16/FoxO. We also analyzed the effect of temperature on insulin-like gene expression. We found that numerous PI3K pathway components and insulin-like peptides are affected by signaling activity, revealing pervasive positive and negative feedback regulation. Reporter gene analysis demonstrated that the daf-2/InsR agonist daf-28 positively regulates its own expression and that other agonists cross-regulate daf-28 transcription through feedback. Our results show that feedback regulation of insulin-like signaling is widespread, suggesting a critical role of feedback in signaling dynamics in this endocrine network and likely others.

genetics↗

bioRxiv2018

Perception of environmental polypeptides in C. elegans activates insulin/IGF signaling and alters lipid metabolism

Food perception affects animal physiology in complex ways. We uncoupled the effects of food perception and ingestion in the roundworm C. elegans. Perception was not sufficient to promote development, but larvae exposed to food without ingestion failed to develop upon return to normal culture conditions. Inhibition of gene expression during perception rescued subsequent development, demonstrating the response to perception without feeding is deleterious. Perception altered DAF-16/FOXO localization, reflecting activation of insulin/IGF signaling (IIS). The insulin-like peptide daf-28 was specifically required, suggesting perception in chemosensory neurons directly regulates peptide secretion. Gene expression and Nile Red staining suggest that perception alters lipid metabolism. Environmental polypeptides are sensed by starved larvae and promote dauer diapause recovery. We conclude that polypeptides are perceived as a food-associated cue, initiating a signaling and gene regulatory cascade that alters metabolism in anticipation of feeding and development, but that this response is detrimental if feeding does not occur.

developmental biology↗