Field of Science

Sunday Protist - Choreocolax:
Shooting nuclei into foreign cytoplasm

The cell, the fundamental unit of life, consists of a package of information-bearing molecules (DNA) wrapped in some material that delineates it from the outer world (lipid membrane). Basically, a cell is a highly organised and compartmentalised bag of fat and acid. Nothing much to see here...

The story is not so simple however. Multiple nuclei occupying one cytoplasm is a fairly common situation, as are holes (channels) between cells in multicellular organisms. This has even led to discussions about using an alternative "Cell Body" concept instead of the conventional cell (Baluska et al. 2004 Annals Bot. (free access)) - although perhaps it's not worth the bother to panic over redefining everything.

Apparently, some coenocytic algal nuclei can survive plasma-membrane-less upon release from a wounded cell. The nucleoplasm is then surrounded by a gelatinous envelope and subsequently forms a plasma membrane and cell wall. (Ram & Babbar 2002, BioEssays). That could be just a special case, a byproduct of coenocytic wound repair mechanisms.

But there is an organism that specialises in firing its nuclei into the host to take it over! (kinda like installing trojans on your computer...) Meet Choreocolax, a filamentous red algal parasite that leeches off Polysiphonia (another red alga).

(Goff & Coleman 1984 PNAS; free access)

It forms 'planetic' nuclei which are then injected into Polysiphonia by forming pit connections. These planetic nuclei then multiply vigorously in the host cytoplasm and 'take over' the cell:
(PN - planetic nucleus; HN - host nucleus)

The molecular aspect of this process must be pretty awesome -- would love to see that thing's genome sequence (sadly unlikely; this thing isn't particularly popular or well-known. Yet.) and hear about the various pathways involved in taking over the host... and how the nucleus can survive in a foreign cytoplasm in the first place!

There's only one lab studying Choreocolax, it appears. That needs to change...


  1. Neat stuff! A couple quick responses:

    For one thing, "foreign" cytoplasm is probably not a relevant concept here. There are plenty of intracellular symbioses, from viruses through prokaryotes through eukaryotes, the latter including secondary plastids as well as parasites. Now, this is not to downplay the amazement factor in discovering individual eukaryotic nuclei acting as life stages for whole organisms, but I think probably the only major biochemical issues in the way of this system evolving are signalling ones, which (both organisms being red algae) are probably not that substantial.

    That being said, I readily admit to speculation here; granting your wish for whole-genome sequencing could well help resolve that. Fortunately, the age of the cheap genome project is not too far off! And in the interim, we are already in the age of the almost-cheap EST project, so the next best thing isn't too unlikely to happen....

  2. Well, being in a foreign cytoplasm as a whole cell (being separated by a membrane) is rather mundane (even prokaryote endosymbiosis of other prokaryotes, as I just read today! O_O! But no one's really looking into that because cancer is cooler, or something); but rather the idea of a naked nucleus in just a nuclear envelope alone somehow surviving in a cytoplasm different from its own. Although they're not that far apart - there's this trend of parasitism of close family members among the red algae, apparently (kinda like H.sapiens...); and that is perhaps quite relevant to cases like this. But meh, still cool!

    So did you just volunteer yourself to do an EST project for Choreocolax? Thanks! =D ^.^

    I'm exempt for I am terrible at anything involving nucleotides. Like genotyping. Fuck genotyping. I swear PCR is controlled by some undetectable forces of voodoo...


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