Biology subjects

Hörning, M.

Publications and source records attributed to Hörning, M..

4 recordsLinked to original sources

bioRxiv2022

The GEF-GAP pair Solo and DLC3 balances Rho activity during endocytic transport

The control of intracellular membrane trafficking by Rho GTPases is central to cellular homeostasis. How defined pairs of guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs) come together to locally balance GTPase activation cycles in this process is nevertheless largely unclear. By performing a microscopy-based RNAi screen we here identify the RhoGEF protein Solo as a counterpart of DLC3, a RhoGAP protein with established roles in membrane trafficking. Biochemical, imaging and optogenetics assays further uncover Solo as a novel regulator of endosomal RhoB. Remarkably, we find that the interplay between Solo and DLC3 controls not only the activity but also total protein levels of RhoB. Together, the results of our study uncover the first functionally connected RhoGAP-RhoGEF pair at endomembranes and place the Solo-DLC3 axis at the core of endocytic trafficking.

cell biology↗

bioRxiv2021

Galvanotaxis of ciliates: Spatiotemporal dynamics of Coleps hirtus under electric fields

Galvanotaxis describes the functional response of organisms to electric fields. In ciliates, the electric field influences the electrophysiology and thus the cilia beat dynamics. This leads to a change of the swimming direction towards the cathode. The dynamical response to electric fields of Coleps hirtus has not been studied since the observations of Verworn in 1890 (1). While galvanotaxis has been studied in other cilitates, C. hirtus exhibit properties not found elsewhere, such as biomineralization-processes of alveolar plates with impact on the intracellular calcium regulation and a bimodal resting membrane potential, which leads unique electrophysiological driven bimodal swimming dynamics. Here, we statistically analyze the galvanotactic dynamics of C. hirtus by automated cell tracking routines. We found that the number of cells that show a galvanotactic response, increases with the increase of the applied electric field strength with a mean at about 2.1 V/cm. The spatiotemporal swimming dynamics change and lead to a statistical increase of linear elongated cell trajectories that point toward the cathode. Further, the increase of the electric fields decreases the mean velocity variance for electric fields larger than about 1.3 V/cm, while showing no significant change in the absolute velocity for any applied electric field. Fully functional galvanotactic responses were observed at a minimum extracellular calcium concentration of 20 {micro}M. The results add important insights to the current understanding of cellular dynamics of ciliates and suggest that the currently accepted model lags the inclusion of the swimming dynamics and the complex calcium regulatory system of the cell. The results of this study do not only extend the fundamental understanding of C. hirtus dynamics, but also open possibilities for technical applications, such as biosensors or microrobots in the future.

biophysics↗

bioRxiv2021

Correlation of mitochondrial TOM core complex stop-and-go and open-closed channel dynamics

The role of lateral diffusion of proteins in the membrane in the context of function has not been examined extensively. Here, we explore the relationship between protein lateral diffusion and channel activity of the general protein import pore of mitochondria (TOM-CC). Optical ion flux sensing through single TOM-CC molecules shows that TOM-CC can occupy three ion permeability states. Whereas freely diffusing TOM-CC molecules are preferentially found in a high permeability state, physical tethering to an agarose support causes the channels to transition to intermediate and low permeability states. This data shows that combinatorial opening and closing of the two pores of TOM-CC correlates with lateral protein diffusion in the membrane plane, and that the complex has mechanosensitive-like properties. This is the first demonstration of {beta}-barrel protein mechanosensitivity, and has direct conceptual consequences for the understanding of the process of mitochondrial protein import. Our approach provides a novel tool to simultaneously study the interplay of membrane protein diffusion and channel dynamics.

biophysics↗

bioRxiv2018

Three-dimensional cell geometry controls excitable membrane signaling in Dictyotelium cells

Phosphatidylinositol (3,4,5)-trisphosphate (PtdInsP3) is known to propagate as waves on the plasma membrane and is related to the membrane protrusive activities in Dictyostelium and mammalian cells. While there have been a few attempts to study the three-dimensional dynamics of these processes, most studies have focused on the dynamics extracted from single focal planes. However, the relation between the dynamics and three-dimensional cell shape remains elusive, due to the lack of signaling information about the unobserved part of the membrane. Here we show that PtdInsP3 wave dynamics are directly regulated by the three-dimensional geometry - size and shape - of the plasma membrane. By introducing an analysis method that extracts the three-dimensional spatiotemporal activities on the entire cell membrane, we show that PtdInsP3 waves self-regulate their dynamics within the confined membrane area. This leads to changes in speed, orientation and pattern evolution, following the underlying excitability of the signal transduction system. Our findings emphasize the role of the plasma membrane topology in reaction-diffusion driven biological systems and indicate its importance in other mammalian systems.

biophysics↗