Unicellular to multicellular transitions

[Pythagorean]

Are there any other examples besides slime molds? It's already quite impressive that slime molds even exhibit cell differentiation!

Are there other cellular communities that exhibit cell differentiation (without necessarily forming a multicellular organism, persay)?

 

[mishrashubham]

Are there other cellular communities that exhibit cell differentiation (without necessarily forming a multicellular organism, persay)?

Volvox is the thing you are looking for then. Perfectly fits your description.
http://www.microscopy-uk.org.uk/mag/artdec03/volvox.html

 

[Pythagorean]

thanks mishra

just two such organisms are well known enough for the Physicsforums sample size?

 

[mishrashubham]

Volvox is quite popular actually. Anyways after some googling I found this.

Organized patterns of cell differentiation occur even in some procaryotes. For example, many kinds of cyanobacteria remain together after cell division, forming filamentous chains that can be as much as a meter in length. At regular intervals along the filament, individual cells take on a distinctive character and become able to incorporate atmospheric nitrogen into organic molecules. These few specialized cells perform nitrogen fixation for their neighbors and share the products with them. But eucaryotic cells appear to be very much better at this sort of organized division of labor; they, and not procaryotes, are the living units from which all the more complex multicellular organisms are constructed.

And this might also help.
http://www.wired.com/wiredscience/2008/07/primitive-micro/

 

[Pythagorean]

Volvox is quite popular actually.

I used bad language. I just meant that I'm surprised there were only two examples of differentiating single-cell communities, but also considering the sample size of physicsforums (it is, after all, not called biologyforums).

 

[mishrashubham]

This time I found names of the specific cyanobacteria which I mentioned earlier.

http://en.wikipedia.org/wiki/Heterocyst

http://en.wikipedia.org/wiki/Anabaena

 

[Pythagorean]

Thanks again! From the wired article, here's the paper. Interesting stuff

http://kinase.com/monosiga/PNAS_proof.pdf

Tyrosine kinase signaling has long been considered a hallmark of
intercellular communication, unique to multicellular animals. Our
genomic analysis of the unicellular choanoflagellate Monosiga brevicollis discovers a remarkable count of 128 tyrosine kinases, 38 tyrosine
phosphatases, and 123 phosphotyrosine (pTyr)-binding SH2 proteins,
all higher counts than seen in any metazoan. This elaborate signaling
network shows little orthology to metazoan counterparts yet displays many innovations reminiscent of metazoans. These include
extracellular domains structurally related to those of metazoan receptor kinases, alternative methods for membrane anchoring and
phosphotyrosine interaction in cytoplasmic kinases, and domain combinations that link kinases to small GTPase signaling and transcription. These proteins also display a wealth of combinations of known
signaling domains. This uniquely divergent and elaborate signaling
network illuminates the early evolution of pTyr signaling, explores
innovative ways to traverse the cellular signaling circuitry, and shows
extensive convergent evolution, highlighting pervasive constraints
on pTyr signaling.

(terrible copypasta job)

 

[Pythagorean]

Found another one:

The Portuguese man o' war is not actually a jellyfish "but a colonial organism made up of many highly specialized minute individuals called zooids." (according to wiki)

http://en.wikipedia.org/wiki/Portuguese_man_o'_war

 

[Enigman]

The portugese man O' wars belong to Siphonophores (which includes Praya Dubia, really long and cool*) which are composed of both polyps and medusae forms of zooids (cnidaria).

some other colonial animals are Bryozoa (moss animals;) and Corals(polyps).

But in all cases the zooids are multicellular AFAIK.
----------
*But portugese Man O' Wars are cooler...enough to be included in Age[/PLAIN] of Mythology: Titans. But that unit can be commanded to move...PMOWs can't move independently...or shoot lightning for that matter.

 

[Enigman]

A Nature article:[URL]http://www.nature.com/scitable...nd-the-evolution-of-multicellularity-14433403
Volvox, Chlamydomonas, and the Evolution of Multicellularity[/URL]

And:

The choanoflagellates are a group of free-living unicellular and colonial flagellate eukaryotes considered to be the closest living relatives of the animals.

http://en.wikipedia.org/wiki/Choanoflagellate
Edit: OK choanoflagellates have already mentioned in the pasta, I see...bah too lazy to delete.

 

[Pythagorean]

Cool, thanks! The evolution of multicellularity was kind of the holy grail of this thread when I first made it 2+ years ago. Never thought to search for that simple combination of words.

Always likes this video, too:



Of course, I don't think "intelligence" is required to explain their behavior as the video implies. Could just be good ol' chemotaxis:
http://www.sciencedirect.com/science/article/pii/S0167278910002617

 

[Ygggdrasil]

Researchers have done laboratory evolution experiments that have gotten unicelular yeast to evolve multicelularity:

Multicellularity was one of the most significant innovations in the history of life, but its initial evolution remains poorly understood. Using experimental evolution, we show that key steps in this transition could have occurred quickly. We subjected the unicellular yeast Saccharomyces cerevisiae to an environment in which we expected multicellularity to be adaptive. We observed the rapid evolution of clustering genotypes that display a novel multicellular life history characterized by reproduction via multicellular propagules, a juvenile phase, and determinate growth. The multicellular clusters are uniclonal, minimizing within-cluster genetic conflicts of interest. Simple among-cell division of labor rapidly evolved. Early multicellular strains were composed of physiologically similar cells, but these subsequently evolved higher rates of programmed cell death (apoptosis), an adaptation that increases propagule production. These results show that key aspects of multicellular complexity, a subject of central importance to biology, can readily evolve from unicellular eukaryotes.

Ratcliff et al. 2012 Experimental evolution of multicellularity. Proc. Natl. Acad. Sci. USA 109: 1595. http://dx.doi.org/10.1073/pnas.1115323109Biofilm formation by bacteria could also be seen as a simple version of the phenomenon you're discussing.

 

[Borek]

I believe I have read somewhere (but won't find it now) that yeast is not a best organism for such a research, as it may have traces of being multicellular in the past, and becoming unicellular back again. Or at least some yeast species do show some multicellular behavior.

 

[Pythagorean]

I believe I have read somewhere (but won't find it now) that yeast is not a best organism for such a research, as it may have traces of being multicellular in the past, and becoming unicellular back again. Or at least some yeast species do show some multicellular behavior.

Apparently, the authors responded to the criticism:

http://blogs.discovermagazine.com/loom/2012/01/18/evolving-bodies-a-storify-follow-up/#.Ush-PvRDuMM