The nucleus remains intact in the plasma

research

The genetic information is separated from the rest of the cell in eukaryotes in the cell nucleus. This spatial separation is given by the nuclear envelope, which consists of two membranes, the inner and outer nuclear membrane. Embedded in this two-membrane system are nuclear pore complexes, the transport openings of the nuclear envelope. These are high-molecular protein complexes - 125 MDa in vertebrates - which bring about the molecular exchange between the cytoplasm and the inside of the cell nucleus.

Schematic representation of the cell nucleus and the nuclear envelope

While in yeast cells the nuclear envelope remains intact during cell division, in animal cells the nuclear envelope collapses when it enters mitosis. At the end of mitosis, it builds up again around the chromatin of the daughter cells. We investigate the molecular mechanisms of the reconstruction of the nuclear envelope and nuclear pore complexes as well as chromatin decondensation. With egg extracts from Xenopus laevis we can simulate, biochemically manipulate and examine these processes in the test tube. This is how we identify key components, define their function in the processes and how they are regulated.

Frogs in our aquariums and the eggs they lay

Nuclear pore structure and function

Nuclear pores mediate protein, RNA and metabolite transport between the cytoplama and the cell nucleus. With a mass of 125 MDa, they are the largest protein complexes we know. The step-by-step coordination of these megastructures from more than 500 individual proteins and how they integrate into the nuclear envelope is a fascinating example of cellular self-organization. Using biochemical and cell biological methods, we define the blueprint for these complexes and their function in the various transport processes. We study the membrane interaction of nuclear pore proteins and how this contributes to the structure of the nuclear pore.

Although nuclear pores have an essential function in all cells, some mutations in nuclear pore proteins cause very specific pathologies, e.g. B. arterial fibrillation, nephrotic syndrome with fatal kidney failure in children or the AAA syndrome, in which the patients show achalsia, alacrima and Addinson’s disease. We characterize how specific mutations in nuclear pore proteins affect very specific cell types and define the molecular mechanisms of the pathologies described.

Formation of a nuclear envelope and nuclear pore complexes in the test tube

further reading

Vollmer B, Lorenz M, Moreno-Andres D, Bodenhöfer M, De Magistris P, Astrinidis SA, Schooley A, Flötenmeyer M, Leptihn S, and Antonin W (2015). Nup153 recruits the Nup107-160 complex to the inner nuclear membrane for interphasic nuclear pore complex assembly. Developmental Cell, 33 (6): 717-728.

Braun DA, Sadowski CE, Kohl S, Lovric S, Astrinidis SA, Pabst WL, Gee HY, Ashraf S, Lawson JA, Shril S, Airik M, Tan W, Schapiro D, Rao J, Choi WI, Hermle T, Kemper MJ , Pohl M, Ozaltin F, Konrad M, Bogdanovic R, Büscher R, Helmchen U, Serdaroglu E, Lifton RP, Antonin W, Hildebrandt F (2016). Mutations in nuclear pore genes NUP93, NUP205 and XPO5 cause steroid-resistant nephrotic syndrome. Nature Genetics, 48 ​​(4): 457-465.

Weberruss M and Antonin W (2016). Perforating the nuclear boundary - how nuclear pore complexes assemble. Journal of Cell Science 129 (24): 4439-4447

Chromatin decondensation at the end of mitosis

In animal cells, the mitotic chromatin is packed fifty times more densely in chromosomes than in the interphase. At the end of mitosis, when a cell nucleus forms again, the chromatin has to be unpacked again so that it can be transcribed and replicated. Although this is an essential process in the life cycle of cells, little is known about it. Using a cell-free system, we identify and characterize chromatin decondensation factors.

Chromatin decondensation in the test tube

Through life cell imaging, often in combination with RNAi-based screening methods, we identify key components of chromatin decondensation, the dynamics of chromatin decondensation and how it is coordinated with other cellular processes that take place over time.

Chromatin decondensation in cells

Further reading:

Magalska, A, Schellhaus, AK, Moreno-Andres, D, Zanini, F, Schooley, A, Sachdev, R, Schwarz, H, Madlung, J, Gerken, J and Antonin, W (2014). RuvB-like ATPases function in chromatin decondensation at the end of mitosis. Developmental Cell, 31 (3): 305-318.

Schellhaus, AK, Magalska, A, Schooley, A, and Antonin, W (2015). A cell free assay to study chromatin decondensation at the end of mitosis. Journal of Visual Experiments (JoVE), 106: doi: 10.3791 / 53407.

Antonin W and Neumann H (2016). Chromosome condensation and decondensation during mitosis. Current Opinion in Cell Biology, 40: 15-22.

Vesicle formation in the nuclear envelope by herpes viruses

Although nuclear pore complexes represent the actual transport channels of the nuclear envelope, herpesviruses ignore this path. They leave the nucleus by forming vesicles on the inner nuclear membrane. These vesicles constrict in the space between the inner and outer nuclear membrane and fuse with the outer nuclear membrane. The virus particle is released in the cytosol. Using minimal membrane systems such as GUVs (giant unilammelar vesicles), we investigate which proteins mediate vesicle formation and constriction and how they accomplish this.

Herpes viruses form nuclear membrane vesicles

Further reading:

Lorenz M, Vollmer B, Unsay JD, Klupp BG, García-Sáez AJ, Mettenleiter TC, and Antonin W (2015). A single herpesvirus protein can mediate vesicle formation in the nuclear envelope. Journal of Biological Chemistry, 290 (11): 6962-6974.

Zeev-Ben-Mordehai, T, Weber soot, M, Lorenz, M, Cheleski, J, Hellberg, T, Whittle, K, El-Omari, K, Vasishtan, D, Dent, KC, Harlos, K, Hagen, W, Klupp, BG, Antonin, W, Mettenleiter, TC, and Grünewald, K (2015). Crystal structure of the herpesvirus nuclear egress complex provides insights into inner nuclear membrane remodeling. Cell Reports, 13 (12): 2645-2652.