Hello,
Amphibians eggs are surrounded of a jelly coat constituted by one to several layers depending on the considered species. The composition of these layers depends on the considered layer and species. The functions of this layers are multiple. Indeed, the jelly coat is for instance known to be involved in fertilization, to avoid polyspermy, to act as a sperm chemoattractant and to play an important role of barrier against UV, infection and contaminants. But, the role of barrier against contaminants is not so clear. Indeed, the complex structure of the jelly coat provides to it an affinity to specific molecules. Therefore, certains molecules are stopped by the layers while others penetrate to the embryos.
In spite of this, most protocole for testing effect of toxicants on amphibians suggest to dejelly the eggs before the exposure. From my point of view, this recommendation lead to a loss of ecological relevance and I'm wondering if dejellying should not be reconsidered.
How about you ? Is there something that I don't see ?
Hi Laurent,
The ASTM FETAX guideline for amphibian developmental toxicity testing states that the jelly coating should be removed immediately following egg-laying by stirring in 2 % v/v L-cystein solution (pH 8.1). The procedure should be stopped the moment the jelly coat has been dissolved, as not to damage the embryos.
The guideline does not specifically describe why we should de-jelly the eggs before testing. However, handling of the (Xenopus) eggs before de-jellying is difficult because they tend to stick to all surfaces. Individual handling of eggs tends to be nearly impossible.
I agree that removing the jelly coat before chemical testing decreases the ecological relevance of the test, because - as you write - the jelly coat has many protective properties. Perhaps other amphibian species have less sticky egg jelly-coats which could be used for individual testing. Or you could attempt to expose whole egg clutches.
Good luck!
Hi Johannes,
Thanks for your reply.
I recently tried to individualize eggs without dejellying and it worked quite easily using two thin forceps. Of course it was sticky but not enough for loosing my patience.
Another way could be to individualize them when jelly coat is more altered like after 2 days.
I think I definitely won't dejelly eggs for my experiments.
Best
Hi Laurent,
Sounds promising! A very interesting study could be to compare toxic responses after exposure to a chemical with either "jellied" or "un-jellied" eggs. Looking forward to hear more about it!
Kind regards
Here is a good example of increased toxicity in presence of jelly. But there is counter examples as well.
Hi Laurent ,I agree that removing the jelly reduces ecological relevance in the toxicity testing. However, one reason could be to create a worst-case (tier 1) laboratory experiment with enhanced exposure. For increasing realism, the next step could be to test eggs with jelly (tier 2). This of course would assume that jelly protects the embryo by lowering exposure.
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