Finally, an enormous thank you to everyone involved! It has been a wonderful collaboration. Thanks also to the @mrclmb.bsky.social core staff. And thanks to Arthur for sharing reagents and data prior to publication and to Steve Bell for coordinating submission. We appreciate it!

In this sense, Sulfolobus cells use a regulatory decision point (analogous to a eukaryotic cell cycle checkpoint) to ensure that they only trigger DNA segregation once they are ready to divide.

Taken together, our data suggest a new model for Sulfolobus cell division: First, CdvA forms a ring. This isn't enough to trigger DNA segregation, though, since this requires the recruitment of a medial ESCRT-III ring, which triggers DNA segregation and defines the axis of DNA segregation.

Nevertheless, using live imaging we observed that while mutant cells can still segregate their DNA in the absence of SegA or SegB, they often suffer serious DNA compaction errors, leading to constricting cells with bridging DNA.

We also used a knockout strategy. SegA, SegB and SegAB deletion strains only observed modest division defects by flow cytometry, implying redundancy in the system.

To explore how ring assembly and DNA segregation might be coupled, we turned our attention to the ParA homologue, SegA, and its partner SegB, using antibodies kindly gifted by @acharlesorszag.bsky.social (see www.biorxiv.org/content/10.1...)

Furthermore, blocking ESCRT-III ring recruitment prevented DNA segregation. These data show that the completion of ESCRT-III ring formation is necessary for cells to segregate their DNA and divide. In addition, ring position determines the axis of DNA segregation.

To do this, we quantified DNA segregation in cells with different ring compositions. While there was little to no DNA segregation in cells with a CdvA-only ring, once cells had recruited a medial ESCRT-III-positive division ring, they tended to have segregated their DNA.

Using coarse-grain molecular dynamic simulations they showed that DNA mobility followed by rapid compaction can aid entropic DNA segregation, even in spherical cells like Sulfolobus. Next, we assessed the relative timing of DNA segregation and division ring formation.

In interphase DNA was associated with the membrane. Then, just before DNA segregation, the DNA became diffuse and mobile, before rapidly compacting into two spatially separated foci. To determine a possible role for these changes, we teamed up with @vsorichetti.bsky.social and Andela Saric.

Like eukaryotic cells, Sulfolobus has an ordered cell cycle with distinct non-overlapping phases. But they lack CDK-cyclins. So how is DNA segregated in archaea? To find out, we imaged DNA and membrane in live dividing cells at 75°C. Unexpectedly, this revealed dynamic changes in DNA organisation.