Biology subjects

Grosshans, J.

Publications and source records attributed to Grosshans, J..

5 recordsLinked to original sources

bioRxiv2018

Automated Segmentation of Epithelial Tissue Using Cycle-Consistent Generative Adversarial Networks

A central problem in biomedical imaging is the automated segmentation of images for further quantitative analysis. Recently, fully convolutional neural networks, such as the U-Net, were applied successfully in a variety of segmentation tasks. A downside of this approach is the requirement for a large amount of well-prepared training samples, consisting of image - ground truth mask pairs. Since training data must be created by hand for each experiment, this task can be very costly and time-consuming. Here, we present a segmentation method based on cycle consistent generative adversarial networks, which can be trained even in absence of prepared image - mask pairs. We show that it successfully performs image segmentation tasks on samples with substantial defects and even generalizes well to different tissue types.

bioinformatics↗

bioRxiv2018

Optochemical control of cell contractility at single cell resolution during tissue morphogenesis

AbstractsThe spatial and temporal dynamics of cell contractility plays a key role in tissue morphogenesis, wound healing and cancer invasion. Here we report a simple, single cell resolution, optochemical method to induce reversible minute-scale cell contractions in vivo during morphogenesis. We employed the photolabile Ca2+ chelator o-nitrophenyl EGTA to induce bursts of intracellular free Ca2+ by laser photolysis. Ca2+ bursts appear within seconds and are restricted to individual target cells. Cell contraction reliably followed within a minute, to about half of the cross-sectional area. Increased Ca2+ levels and contraction were reversible and the target cells further participated in tissue morphogenesis. Cell contractions are paralleled with non-muscle myosin-II accumulation in the apico-medial cortex, indicating that Ca2+ bursts trigger non-muscle myosin II activation. Our approach can be easily adapted to many experimental systems and species, as no specific genetic elements are required and a widely used reagent is employed.

developmental biology↗

bioRxiv2017

A "molecular guillotine" reveals an interphase function of Kinesin-5

Motor proteins are important for transport and force generation in a variety of cellular processes and morphogenesis. Here we design a general strategy for conditional motor mutants by inserting a protease cleavage site at the \"neck\" between the head domain and the stalk of the motor protein, making the protein susceptible to proteolytic cleavage at the neck by the corresponding protease. To demonstrate the feasibility of this approach, we inserted the cleavage site of TEV protease into the neck of the tetrameric motor Kinesin-5. Application of TEV protease led to a specific depletion and functional loss of Kinesin-5 in Drosophila embryos. By this, we revealed that Kinesin-5 stabilized the microtubule network during interphase in syncytial embryos. The \"molecular guillotine\" can potentially be applied to many motor proteins due to the conserved structures of kinesin, dynein and myosin with accessible necks.\n\nAuthor summaryWe design a general strategy for conditional motor mutants by inserting a protease cleavage site between head and stalk domain of the motor protein, making it susceptible to specific proteolytic cleavage. We demonstrate the feasibility of the approach with the motor Kinesin-5 and the protease TEV in Drosophila embryos. This approach can potentially be applied to motor proteins kinesin, dynein and myosin due to the conserved structures.

developmental biology↗

bioRxiv2017

Expression of lamina proteins Lamin Dm0 and Kugelkern suppresses stem cell proliferation

The nuclear lamina is involved in numerous cellular functions, such as gene expression, nuclear organization, nuclear stability, and cell proliferation. The mechanism underlying the involvement of lamina is often not clear, especially in physiological contexts. Here we investigate how the farnesylated lamina proteins Lamin Dm0 and Kugelkern are linked to proliferation control of intestinal stem cells (ISCs) in adult Drosophila flies by loss-of-function and gain-of-function experiments. We found that ISCs mutant for Lamin Dm0 or Kugelkern proliferate, whereas overexpression of Lamin Dm0 or Kugelkern strongly suppressed proliferation. The anti-proliferative activity is, at least in part, due to suppression of Jak/Stat but not Delta/Notch signalling. Lamin Dm0 expression suppresses Jak/Stat signalling by normalization of about 50% of the Stat target genes in ISCs.\n\nAuthor summaryThe nuclear lamina is a protein meshwork that lies beneath the inner side of the nuclear membrane and interacts with nuclear pores, chromatin and the cytoskeleton. Changes in proteins of the nuclear lamina cause a wide range of diseases which are often not well understood. It is hypothesized that impairment of stem cell function, as a result of lamina changes, might play a key role in some of those diseases. Here we use the well characterized Drosophila midgut as a system to investigate the role of lamina proteins Lamin Dm0 and Kugelkern on stem cell proliferation.

developmental biology↗

bioRxiv2017

Protein phosphatase V ensures timely cell cycle remodeling during the mid-blastula transition in Drosophila

Cell cycle remodeling from fast nuclear cycles to a generic cell cycle mode is a major feature of the mid-blastula transition (MBT) in Drosophila. Remodeling occurs when Twine/Cdc25 falls below a critical threshold. Timing is based on Twine destabilization induced by zygotic transcription. It is conceivable that appropriate starting levels are also important for timely reaching the threshold. Mechanisms for controlling Twine levels at the onset of MBT are unknown. Here we identify a function of the protein phosphatase V in this mechanism. Twine was increased in PpV mutants, whereas the decay rate was comparable to wildtype. PpV mutants frequently underwent an extra nuclear division. We detected PpV-dependent phosphosites in Twine. Phosphosite mutants contain higher Twine levels and frequently underwent an extra nuclear division, comparable to PpV mutants. Our data support a model that the cell cycle remodeling is controlled by induced destabilization and PpV-d ependent control of Twine levels.

developmental biology↗