WEBVTT

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We are now in our laboratory in Canberra. 
The sponges have spent the night 


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equilibrating to the conditions in the 
aquarium. We are using a mixture of 


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natural and artificial sea water and maintain
 the tanks at 16 to 18°C depending on the 


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 time of the year. While <i>Sycon capricorn</i> does
not reproduce in our tanks, we can maintain


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 the sponges for several months so we
 always have sponges for experiments.


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You can clearly see the two different 
morphotypes, branching and nonbranching,


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 which we believe are both<i> Sycon capricorn</i>.

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I am picking a nonbranching sponge
 for our regeneration experiment. 


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This sponge has a clear radial symmetry
 with only one osculum at the apical end.


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Its basal end has previously been
 attached to the holdfast of kelp


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 or to a rock at the sea bottom. But in the 
aquarium it was simply pressed into the sand. 


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The sponge is placed in a Petri dish in sea
 water using very simple tools, a pair of 


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foreceps and a sharp scalpel blade. 
I will cut it into rings of tissue. 


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It is very much like slicing a carrot.

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Each of these slices is capable of regenerat-
ing a new osculum at the top and a new


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 base at its bottom as you have seen for <i>Sycon</i>
<i> ciliatum</i> in the lecture on sponge regeneration.


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But sponges are capable of more
 than regeneration from slices.


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We can dissociate these slices into single cells
 and they will aggregate to rebuild new sponges.


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 We are using a 40 micron cell strainer. 
The slices are placed in a bit of sea water 


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and a pestle is used to 
push the cells through it.


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This rather brutal method produces a
 suspension of cells, cell clusters, and 


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some broken spicules. We will now use a
 microscope to see how the cells look and 


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what are they trying to do.

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As expected, we can see some cell clusters, 
some single cells, and some spicules in the mix,


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 and if we zoom in on some of these 
cells, we can see a beating flagellum.


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 This is a choanocyte, although we cannot 
see the colour at this resolution.


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This is a real-time video.

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And this is a time-lapse video which was
 started 20 minutes after disassociation.


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The cells lost flagella already and they
 became amoeboid. You can see very active


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 movement of the cells. As they meet each 
other, they remain attached to each other, 


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forming larger and larger aggregates.

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And this is a one week-old aggregate. 
You can see it is a smooth sphere with


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 the surface made of pinacocytes. 
They have either migrated there when


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 the aggregate cells were sorting or are 
derived from cells that have previously 


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been choanocytes and have transdifferent-
iated based on their position in the aggregate. 


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Note that there are no 
spicules visible at this stage.


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And after another week, many aggregates
 such as this one have formed spicules. 


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At this stage they are only
 simple diactine spicules.


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 The aggregates at this stage clearly 
resemble juveniles developing from larvae.


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It still needs a few days to become a
 functional sponge, but what we could 


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clearly observe is that dissociating 
sponges into single cells does not kill them.


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 They have an amazing capacity 
of self-organisation.


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 I wish we humans 
were able to do it too.