Biology subjects

Schnittger, A.

Publications and source records attributed to Schnittger, A..

24 records · Page 2Linked to original sources

bioRxiv2020

Closure motif-mediated state changes of the HORMA protein ASY1

Meiotic HORMA domain-containing proteins (HORMADs) are key components of the chromosome axis and play an essential role in meiosis in many organisms. The meiotic HORMADs, including yeast Hop1, mouse HORMAD1 and HORMAD2, and Arabidopsis ASY1, assemble along chromosomes at early prophase and the closure motif at their C-termini has been hypothesized to be instrumental for this step by promoting HORMAD oligomerization. In late prophase, ASY1 and its homologs are progressively removed from synapsed chromosomes promoting chromosome synapsis and recombination. The conserved AAA+ ATPase PCH2/TRIP13 has been intensively studied for its role in removing HORMADs from synapsed chromosomes. In contrast, not much is known about how HORMADs are loaded onto chromosomes. Here, we reveal that the PCH2-mediated dissociation of the HORMA domain of ASY1 from its closure motif is important for the nuclear targeting and subsequent chromosomal loading of ASY1. This indicates that the promotion of ASY1 to an unlocked state is a prerequisite for its nuclear localization and chromosomal assembly. Likewise, we find that the closure motif is also necessary for the removal of ASY1 by PCH2 later in prophase. Our work results in a grand unified model for PCH2 and HORMADs function in meiosis.

cell biology↗

bioRxiv2020

Functional analysis of the chromosomal passenger complex in Arabidopsis

A key regulator of cell division in all eukaryotes is the kinase Aurora B, which is encoded by the Aurora 3 (AUR3) gene in Arabidopsis. Aurora B has at least two central functions during cell division. On the one hand, it is essential for the correct, i.e. balanced, segregation of chromosomes in mitosis and meiosis by controlling kinetochore function. On the other hand, Aurora B acts at the division plane, where it is necessary to complete cytokinesis. To accomplish these two spatially distinct functions, Aurora B in animals is guided to its sites of action by Borealin, INCENP, and Survivin that build together with Aurora B the chromosome passenger complex (CPC). However, besides Aurora homologs, only a candidate gene with restricted homology to INCENP has so far been described in Arabidopsis raising the question whether there exists a full complement of the CPC in plants and how Aurora homologs are targeted subcellularly. Here, we have identified and functionally characterized a Borealin homolog, BOREALIN RELATED (BORR), in Arabidopsis. This, together with detailed localization studies including the putative Arabidopsis INCENP homolog, supports the existence of a CPC in plants.

cell biology↗

bioRxiv2019

Patronus is the elusive plant securin, preventing chromosome separation by antagonizing separase

Chromosome distribution at anaphase of mitosis and meiosis is triggered by separase, an evolutionarily conserved protease. Separase must be tightly regulated to prevent the untimely release of chromatid cohesion and disastrous chromosome distribution defects. Securin is the key inhibitor of separase in animals and fungi, but has not been identified in other eukaryotic lineages. Here, we identified PATRONUS1 and PATRONUS2 (PANS1 and PANS2) as the Arabidopsis homologues of securin. Disruption of PANS1 is known to lead to the premature separation of chromosomes at meiosis, and the simultaneous disruption of PANS1 and PANS2 is lethal. Here, we show that PANS1 targeting by the anaphase-promoting-complex is required to trigger chromosome separation, mirroring the regulation of securin. We showed that PANS1 acts independently from Shugosins. In a genetic screen for pans1 suppressors, we identified SEPARASE mutants, showing that PANS1 and SEPARASE have antagonistic functions in vivo. Finally, we showed that the PANS1 and PANS2 proteins interact directly with SEPARASE. Altogether, our results show that PANS1 and PANS2 act as a plant securin. Remote sequence similarity was identified between the plant patronus family and animal securins, suggesting that they indeed derive from a common ancestor. Identification of patronus as the elusive plant securin illustrates the extreme sequence divergence of this central regulator of mitosis and meiosis.

cell biology↗

bioRxiv2019

SWITCH 1/DYAD is a novel WINGS APART-LIKE antagonist that maintains sister chromatid cohesion in meiosis

Mitosis and meiosis both rely on cohesin, which embraces the sister chromatids and plays a crucial role for the faithful distribution of chromosomes to daughter cells. Prior to the cleavage by Separase at anaphase onset, cohesin is largely removed from chromosomes by the non-proteolytic action of WINGS APART-LIKE (WAPL), a mechanism referred to as the prophase pathway. To prevent the premature loss of sister chromatid cohesion, WAPL is inhibited in early mitosis by Sororin. However, Sororin homologs have only been found to function as WAPL inhibitors during mitosis in vertebrates and Drosophila. Here we show that SWITCH 1/DYAD defines a novel WAPL antagonist that acts in meiosis of Arabidopsis. Crucially, SWI1 becomes dispensable for sister chromatid cohesion in the absence of WAPL. Despite the lack of any sequence similarities, we found that SWI1 is regulated and functions in a similar manner as Sororin hence likely representing a case of convergent molecular evolution across the eukaryotic kingdom.

cell biology↗

bioRxiv2018

Efficient reverse breeding by VIGS-mediated transient crossover reduction

F1 heterozygotes are traditionally generated by crossing homozygous parental lines. The opposite is achieved through reverse breeding, in which parental lines are generated from a heterozygote. Reverse breeding can be used to develop new F1 hybrid varieties without having prior access to homozygous breeding lines. For successful reverse breeding, the heterozygotes homologous chromosomes must be divided over two haploid complements, which is achieved by suppression of meiotic crossover (CO) recombination. We here show two innovations that facilitate efficient reverse breeding. Firstly, we demonstrate that downregulation of CO rates can be accomplished using virus-induced gene silencing (VIGS). We obtain transgene-free parental lines for a heterozygote in just two generations. Secondly, we show that incomplete CO suppression opens up several alternative strategies for the preservation of hybrid phenotypes through reverse breeding.

plant biology↗

bioRxiv2018

Live cell imaging of meiosis in Arabidopsis thaliana - a landmark system

Meiosis is essential for sexual reproduction and key to the generation of genetic diversity. To reveal the robustness of meiocyte differentiation and progression through meiosis, we have here established a live cell imaging setup to follow the dynamics of individual male meiocytes in Arabidopsis. Our method is based on the concomitant visualization of microtubules and a meiotic cohesion subunit that allowed following five cellular parameters: cell shape, nucleus position, nucleolus position, chromatin condensation and microtubule array. We find that the states of these parameters are not randomly associated and identify 11 states, referred to as landmarks, that occur much more frequently than closely related states, indicating that they are convergent points of meiotic progression. With this, the here-presented landmark system represents a novel method to analyze meiosis not only allowing a high-temporal dissection but also providing new criteria to evaluate mutants or environmental effects on meiosis.

cell biology↗