I am currently working with Atlantic salmon from egg to post-smolt. To keep options open in regard to RNA conservation I have chosen to use the relatively new fixative PAXgene Tissue Fix and tissue stabilizor.
The litterature I have found testing PAXgene (vs formalin etc) use tissues from humans or rodents, i.e. warm tissues. Going from 37oC to room temperature slows down the cellular processes, while going from 4-12oC in the case of coldwater fish will in turn increase the speed of the cellular processes. Does anyone have experience with fixating cold tissue?
In the protocol PAXgene fixative is claimed to penetrate the tissue with a speed of 1 mm per 30 minutes. We have, however, seen some separation of the layers of the gill and intestine that we did not observe in fomalin fixed fish that were otherwise handeled the same. These fish (2 cm long and max 4 mm thick across the scull) were fixated for 24 h in PAXgene fix before the stabilizer were added and the tissue stored at -20oC. Formalin fixed fish were stored in formalin for more than a month in room temperature. I have also fixed eggs (5-6 mm) in PAXgene for minimum 2 h, but worry now that this is not enough. I did see a colour change (whitening) of the embryo quicky after the egg were added to the fixative, and took this as an indication of the fixative penetrating the eggshell.
There are of course differences between tissue fixated with different fixatives. As formalin is the gold standard PAXgene fixed tissue is often judged as better or worse than formalin. Effort is taken to reveal exactly how the difference in fixative manifests in different tissue using different techniques (dyes, IHC, FISH etc). In these tests mammalian tissues are used. Do you think fish tissue would behave significantly different?
Does anyone have experience with fixating fish tissue with PAXgene tissue fix?
Any thoughts would be appreciated!
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