Signal transduction

Summary

Signal transduction is the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events. Most commonly, protein phosphorylation is catalyzed by protein kinases, ultimately resulting in a cellular response. Proteins responsible for detecting stimuli are generally termed receptors, although in some cases the term sensor is used. The changes elicited by ligand binding (or signal sensing) in a receptor give rise to a biochemical cascade, which is a chain of biochemical events known as a signaling pathway. When signaling pathways interact with one another they form networks, which allow cellular responses to be coordinated, often by combinatorial signaling events. At the molecular level, such responses include changes in the transcription or translation of genes, and post-translational and conformational changes in proteins, as well as changes in their location. These molecular events are the basic mechanisms controlling cell growth, prolifer

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https://en.wikipedia.org/wiki/Signal_transduction

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In this study, the fission yeast Schizosaccharomyces pombe was used as a model system to study the cellular signaling that underlies cell cycle progression. Phosphorylation plays an important part in the regulation of this process. Kinases catalyze the transfer of a phosphate group to a substrate, which may regulate its activity. Protein phosphatases oppose the activity of protein kinases; the balance of their activities regulates signaling flux in many signaling pathways. The Septation Initiation Network (SIN) is a signaling cascade that regulates cytokinesis in fission yeast. SIN signaling is triggered by a GTPase and is transduced by three protein kinases; phosphorylation plays an important role in controlling SIN signalling. Numerous genetic screens and biochemical analyses have identified phosphatases and kinases that regulate the SIN. The protein phosphatases Calcineurin/Protein Phosphatase 2B (PP2B) and Flp1p promote SIN signaling, while PP2A is a SIN inhibitor. PP2A is conserved and is activated by the chaperone Phosphatase Two A Phosphatase Activator (PTPA). S. pombe has two PTPA-related genes, ypa1 and ypa2; the deletion mutant of the latter rescues SIN mutants which cannot undergo cytokinesis, consistent with PP2A opposing SIN signaling. The phenotype of the deletion mutant of ypa2, indicates that it is involved in the control of cell polarity, cell growth, mitotic commitment and cytokinesis. In this study, we characterized the hypomorphic allele ypa2-S2 which rescues SIN mutants, but is otherwise largely normal. ypa2-s2 was used as bait in a synthetic genetic array screen, to identify genes whose products compensate for reduced function of Ypa2p. A large number of hits were identified, of which approximately ninety percent are novel genetic interactors of ypa2. Validation studies indicated that eighty percent of the interactions seen in the high-throughput screen can be reconstructed. The identified genes regulate several biological processes, including signal transduction and protein phosphorylation. This prompted us to further characterize the roles of Ckb1p and Flp1p, in regulating cytokinesis signaling. Ckb1p is a regulatory subunit for Casein Kinase II (CK II), which was previously implicated in polar growth. The phenotype of the mutant ypa2-S2 ckb1-â indicates that Ckb1p, similar to Ypa2p, contributes to the regulation of mitotic commitment and cytokinesis signaling. Furthermore, ckb1-â showed negative genetic interaction with PP2A and SIN mutants. Flp1p is a protein phosphatase that was reported to regulate mitotic commitment and to promote SIN signaling. The double mutant between ypa2-S2 and flp1-â showed cell separation defects and phenotypic analysis of double mutants between flp1-â and PP2A mutants indicates that these phosphatases cooperate in cell separation. Overall, this work has uncovered novel facets of the regulation of cytokinesis in S. pombe, implicating CK II in controlling SIN signaling, and uncovering cooperative interactions between different phosphatases in controlling cytokinesis.

EPFL2016

Epithelial stem cells and mechanical signal transduction

Vincent Bernard Cattin

Hair follicles are cutaneous structures characteristic of mammals. These sensitive organs cycle and contain multipotent epithelial stem cells which are implicated in hair growth and hair cycle. A single whisker follicle of the rat hosts up to 1500 stem cells, many more than necessary to regenerate the entire follicle throughout the animal's life. These cells are preferentially located in the most innervated region of the hair follicle. We hypothesised that stem cells might have an additional function aside from tissue renewal: stem cells may be involved in the mechanical signal transduction between hair follicle and afferent nervous system. This supplemental role may either take place through the interaction of the multipotent epithelial stem cells with nerve endings, or through neuroepithelial Merkel cells acting as intermediates. Merkel cells are located in the basal layer of the whisker follicle outer root sheath (ORS) and share a close relationship with their neighbouring nerve endings. These cells specifically express the transcription factor Math1 and their function is poorly understood. We demonstrate here by clonal analysis and transplantation assays that Merkel cells are not derived from epithelial stem cells. In addition, Math1-expressing cells isolated from the epidermis are unable to form colonies and to participate in the generation epidermal lineages when transplanted, failing to show stemness properties. Furthermore, when cultured in conditions that favour the growth of neurospheres, they are unable to proliferate, revealing a different behaviour than that of skin-derived neural crest cells. We also demonstrate that multipotent epithelial stem cells express several proteins implicated in glutamate neurotransmission, as well as other molecules usually found in the nervous system. The expression of NMDAR and AMPAR subunits, as well as their scaffolding proteins and neurotransmitter vesicular transport-implicated proteins are uncovered for the first time in the multipotent epithelial stem cells from the bulge. Our results support the mechanical signal transduction hypothesis and confirm the increasingly important role of the recently described neural-like structures of the skin. This work paves the way for a better comprehension of multipotent epithelial stem cell behaviour and stem cell-related pathologies.

EPFL2008

First Biopotential Recordings from a Liquid Crystal Optrode

Han Wang

One of the goals of the Neural Engineering System Design (NESD) program in the United States and of similar programs around the world is to develop an interface able to read from one million neurons in parallel. This is well beyond the capabilities of traditional multi-electrode arrays (MEAs), which are inherently limited in both spatial resolution and number of channels, due to issues with power dissipation and wiring.(1,2) To overcome these roadblocks our group has proposed a novel optrode array that measures electrical activity and uses light for both signal transduction and transmission, thus decoupling the bio-potentials from the signal acquisition circuitry.(3) The technology relies on the sensitivity of a particular class of liquid crystals (LCs) to small electric fields and is analogous to a LC display, where the intensity of each pixel (optrode, in our case) is controlled by the electrical activity of the biological tissue. Here, we present the first use of such a transduction mechanism to record from cardiac tissue and investigate stimulus artifact suppression in rabbit sciatic nerve. Our results pave the way to the development of high-density high-channel-count optrode arrays for electrophysiology studies and brain-machine interfaces.

SPIE-INT SOC OPTICAL ENGINEERING2019

EPFL2016

Epithelial stem cells and mechanical signal transduction

Vincent Bernard Cattin

EPFL2008