Geisler, Florian et al. (2021) International Worm Meeting "Perturbed intermediate filament regulation causes aggregate toxicity"

Leube, Rudolf, Remmelzwaal, Sanne, Richardson, Christine, Geisler, Florian, Boxem, Mike

[International Worm Meeting, 2021]

Intermediate filaments are major components of the metazoan cytoskeleton. A long-standing debate concerns the question whether intermediate filament network organization only reflects or also determines cell and tissue function and dysfunction. This is particularly relevant for aggregate-forming diseases involving intermediate filaments. Using C. elegans as a genetic model organism, we have recently described mutants of signaling and stress response pathways with perturbed intermediate filament network organization. In a mutagenesis screen, we now identify the intermediate filament polypeptide IFB-2 as a highly efficient suppressor of these phenotypes restoring not only intestinal morphology but also rescuing compromised development, growth, reproduction and stress resilience. Ultrastructural analyses show that downregulation of IFB-2 leads to depletion of the aggregated intermediate filaments. The findings provide compelling evidence for the toxic function of deranged intermediate filaments and reveal novel insights into the cross talk between signaling and structural functions of the intermediate filament cytoskeleton.

Geisler, Florian et al. (2010) C. elegans: Development and Gene Expression, EMBL, Heidelberg, Germany "The intermediate filament organizer IFO-1 is a multifunctional linker of the intestinal cytoskeleton"

Geisler, Florian, Bonn, Barbara, Leube, Rudolf, Bossinger, Olaf, Felkl, Marco, Keul, Dominik

[C. elegans: Development and Gene Expression, EMBL, Heidelberg, Germany, 2010]

The lumen of the C. elegans intestine is surrounded by the resilient endotube that is mainly composed of F-actin and six different intermediate filament proteins (e.g. IFC-2 and IFB-2). The conspicuous intestine-specific expression pattern of IFB-2::CFP translational fusion makes this organ ideally suited to identify intermediate filament organizers (IFO). After chemical mutagenesis, we succeeded in the identification of several alleles of ifo-1, which are associated with a highly impaired organization of intestinal intermediate filaments and also display defects in the organization of F-actin. To elucidate the mechanism of ifo-1 function in vivo, we performed a classical suppressor screen, used yeast two hybr id analyses, accomplished RNAi by feeding against several F-actin organizers and generated anti-IFO-1 antibodies. In this way, we isolated suppressor strains, identified potential binding partners of IFO-1, determined cross-talk between the actin and intermediate filament cytoskeleton and examined IFO-1 expression. Taken together, we conclude that IFO-1 is a versatile and multifunctional cytoskeletal linker in the C. elegans intestine.

Remmelzwaal, Sanne et al. (2021) International Worm Meeting "BBLN-1 is essential for intermediate filament organization and apical membrane morphology"

Jarosinska, Olga, Leube, Rudolf, van der Horst, Suzanne, Boxem, Mike, Altelaar, Maarten, Ramalho, Joao, Pasolli, Milena, Akhmanova, Anna, Stucchi, Riccardo, Remmelzwaal, Sanne, Richardson, Christine, Geisler, Florian, Kroll, Jason

[International Worm Meeting, 2021]

Epithelial tubes are essential components of metazoan organ systems that control the flow of fluids and the exchange of materials between body compartments and the outside environment. The size and shape of the central lumen confer important characteristics to tubular organs and need to be carefully controlled. Here, we identify the small coiled-coil protein BBLN-1 as a regulator of lumen morphology in the C. elegans intestine. Loss of BBLN-1 causes the formation of bubble-shaped invaginations of the apical membrane into the cytoplasm of intestinal cells, and abnormal aggregation of the subapical intermediate filament (IF) network. BBLN-1 interacts with IF proteins and localizes to the IF network in an IF-dependent manner. The appearance of invaginations is a result of the abnormal IF aggregation, indicating a direct role for the IF network in maintaining lumen homeostasis. Finally, we identify bublin (BBLN) as the mammalian ortholog of BBLN-1. When expressed in the C. elegans intestine, bublin recapitulates the localization pattern of BBLN-1 and can compensate for the loss of BBLN-1. In mouse intestinal organoids, bublin localizes subapically, together with the IF protein keratin 8. Our results therefore may have implications for understanding the role of IFs in regulating epithelial tube morphology in mammals.

Meng, J. et al. (2017) International Worm Meeting "A two-pore potassium channel regulates C. elegans locomotor behaviors."

Boulin, T., Mercier, M., Zhen, M., Hung, W., Mouridi, S., Meng, J.

[International Worm Meeting, 2017]

The resting membrane potential (RMP) is a key determinant of neuronal excitability1. The two-pore potassium (K2P) channel family has been shown to affect the RMP by conducting the background potassium current2. While many subfamilies of K2P channels have been identified molecularly, less is known about their modulation and physiological functions. C. elegans genome has 47 encoding K2P channel genes, providing an excellent experimental platform to examine and compare the diversity of cellular and physiological functions of K2P family channels. We have identified loss-of-function mutations in a putative two-pore potassium channel, TWK-40, that lead to exaggerated body bends, and increased reversals during locomotion. We find that TWK-40 is expressed and functionally required primarily in premotor interneurons to regulate the motor patterns. We further discover that optogenetical activation of the premotor interneurons may only partially mimic the effect of the endogenous changes of the RMP. I will present ongoing studying on how TWK-40 regulates locomotor behaviors in C. elegans. Reference 1. Hille, Bertil. Ion channels of excitable membranes. Vol. 507. Sunderland, MA: Sinauer, 2001. 2. Lesage, Florian, and Michel Lazdunski. "Molecular and functional properties of two-pore-domain potassium channels." American Journal of Physiology-Renal Physiology 279.5 (2000): F793-F801.

Ozdemir, Isa et al. (2021) International Worm Meeting "Regulation of transgenerational epigenetic H3K27me3 inheritance"

Steiner, Florian, Delaney, Kamila, Wenda, Joanna, Ozdemir, Isa

[International Worm Meeting, 2021]

A crucial process in life is the ability of cells to pass on information to their descendants. This transmission can occur at several levels from genetics to epigenetics. Epigenetic inheritance refers to the heritable phenotypes affected by gene expression without altering the DNA sequence and occurs through various factors including histone modifications. Interruption of this transmission process can lead to severe developmental defects and fertility diseases. Methylation of histone H3 at position 27 (H3K27me3) is an epigenetic mark that is associated with heterochromatin and repressed gene expression. Several studies have demonstrated that the genomic patterns of H3K27me3 can be inherited from one generation to the next by depositing H3K27me3 histones and PRC21. However, the limits of this inheritance are difficult to test because PRC2 mutants are maternal-effect sterile in C. elegans. We have recently shown that the expression of an H3.3K27M mutant acts in a dominant-negative manner and alters genomic H3K27me3 patterns and distribution of PRC2 and results in infertility phenotypes in C. elegans2. We used this strain to follow the trans-generational inheritance of the H3.3K27M-induced phenotypes. Strikingly, we observed that the altered patterning of H3K27me3 and the fertility defects are heritable for multiple generations after the H3.3K27M mutation is lost. These findings were also validated in a tetracycline-inducible system where we can abruptly switch on and off the H3.3K27M expression. We performed a targeted RNAi screen in our tetracycline-inducible system and detected several enhancer and suppressor modifiers of H3.3K27M defects such as chromatin remodeling complexes, the nuclear RNAi pathway, and histone writer and reader complexes. Overall, our results revealed that the transmission of H3K27me3 is an epigenetically programmed event that can last for generations and that several biological pathways seem to be involved in the regulation of transmission of H3K27me3 patterns across generations. 1. L. J. Gaydos, W. Wang, S. Strome. H3K27me and PRC2 transmit a memory of repression across generations and during development. Science 345, 1515-1518 American Association for the Advancement of Science (AAAS), 2014. 2. Kamila Delaney, Maude Strobino, Joanna M. Wenda, Andrzej Pankowski, Florian A. Steiner. H3.3K27M-induced chromatin changes drive ectopic replication through misregulation of the JNK pathway in C. elegans. Nature Communications 10 Springer Science and Business Media LLC, 2019.