I think they can be clubs cells or alarm substance cell but they have lost their contents during the histological processing.

I can suggest to you to observe the skin in fresh smear, or make microtome cryostat sections to stain the material inside.

These types of structures are usually some type of storage.  There would be more vascularization if there was some type of exchange (osmoregulation) function.  I would lean towards mucus storage or something like that.  Are lumpfish capable of producing large amounts of mucous in a short time period?  If there is an analogous structure in hagfish that would make sense.  I'm not sure what else they might use for storage in the skin. 

I think Christopher may be right. I have no experience with fishes, but this section seems to be stained with Ehrlich hematoxylin and eosin (very nice section!). But how was it fixed? Try a PAS stain and use a fixative that does not solve the mucus (Bouin's fluid may be OK for this purpose).

I agree with them but try more sections to confirm if u get nucleus. also the content of the vacuoles should be subjected to further stains. is there any report of eosinophillic club cells in this species?

I think they can be clubs cells or alarm substance cell but they have lost their contents during the histological processing.

I can suggest to you to observe the skin in fresh smear, or make microtome cryostat sections to stain the material inside.

Almost definitely  "club" or alarm substance cells. You have already identified the mucous glands, so you can exclude that option. I doubt the cells are poison glands associated with the spines due to lack of staining with H and E as seen in poisonous amphibians for eg.

I would agree that they are likely mucus cells of some type...I would try serially sectioning through the block to see if  you can pick up more detail of the cytoplasm. I think you have sectioned all the way through from your image. I have seen similar structures in winter flounder skin. Also try Alcian blue or Schiffs reagent to help identify the mucus cells more difinitively. Mucus has been shown to be a good source of antimicrobial peptide in some species..it would be interesting to look at that in lumps. Good luck.

Hi Adrien,

Reminds me a reedfish club cells. Serial sections will be needed to see whether there is a nucleus or cytoplasm fragments.  How regular do you see these structures in triplet? Can you also shoot a lower magnification from the same sample to give us a bit more idea how larger portion of the sample looks like. BTW, nice section!

Best regards,

Ivan

I agree that they are likely epidermal club cells or alarm substance cell.

it may be club or alarm cells

I believe it is one kind of mucus storage structure. However, you should use other types of histology label. I suggest PAS staining!

It is also possible that these are sacciform cells, which can have a cyst-like appearance in some fish species (e.g., in gadoids). The precise functions of these cells are unknown, but they may produce toxic or repellent anti-predator substances in some species, and regulatory peptides or infraspecific alarm pheromones in others.

For references, see e.g.:

Bereiter-Hahn, Matoltsy, and Richard (2013) Biology of the Integument 2: vertebrates, Springer.

Elliott, DG (2011) Functional anatomy of the integument, p.p. 476-488 In Farrell, A.P. (ed.) Encyclopedia of Fish Physiology,: From Genome to Environment, Academic Press.

I agree with dr .Diane Elliot that the function of these cells is unclear. But in my practice I observed such pictures in fish in stressful conditions of environment.

Aren't these structures a little too big to be just club cells? (Compare with the surrounding cells and nuclei.) I have the impression that these are the swollen terminal parts of ducts of glands lying under the stratum compactum. You should find the glands there and the opening of the ducts in neighboring sections. If the content is mucous, PAS may give an indication (also suggested by Diogenes). I do not speculate on fuction…

Dear all,

I think it is time to ask Adrian about the primary fixation technique he used.

As of my experience this perhaps could help in determination of the nature of the already empty "hole", or "lumen / lumina" (if one adopts Ernest Schockaerts opinion of "cross sections of gland ducts",  *)see bottom line ).

Depending on primary fixation (which most probably only was   FA/Formalin (hopefully at least NBF(neutral buffered Formalin),  if not ) there is to be expected: 

1) not all tissue components will be fixed= conserved AND permanently stabilized (retained) satisfactorily (this e.g. for sure matters for certain glycoconjugates as well as lipids) and hence will not be included during OR will not  withstand the following dehydration and other harsh processing steps into paraffin.

 2) of many (mostly the ) substances (fixed most weakly by only  Formalin/FA/PFA)  during dehydration (especially in the higher alcohol steps), as well as in xylene (or similar organic clearing solvents) takes place.

So everybody knows e.g. about the "emptiness" of lipid droplets/lipid vacuoles in tissue sections of histologically processed specimens.

Therefore it would be advisable (because this IMHO is the possibly most rapid technique for a proof) to perform cryofixation and cryosectioning, followed by mucin and or glycoconjugates' stains but including also stain(s) for lipidic material.

If there then is found / retained "distinct material" left in the "sacs" "holes" "lumina" or "empty spaces" one should be able to get some clue about the nature of that "secretions" Adrian (we) don't see in the image attached to the request. 

If the round structures also in cryosections are , it points perhaps to an only hydrous or highly watersoluble (protein-free?) component / content (whatever that would  / could be then).

For evaluation of the nature of these sacciform structures after "chemical fixation" I recommend to compare at least two if not three different fixatives  (perhaps one acidic, another Bouin's or Zamboni's, and as third fixative it might be of benefit to use a combination of phosphate-buffered (e.g. KARNOVSKY-fixative as used for TEM-spec-preparation + some lipid-retentive mordanting agent like PPD ) or even acrolein-containing fixative combinations.

Cave: Acrolein is a very effective and therefore also hazardous chemical which is to be handled and used  very carefully and cautiously. But it is a very effective and most rapidly penetrating (simplest unsaturated aldehyde) fixative which is brought into play when trying to localize certain fragile or highly soluble enzymes.

My two cents,

Best regards and best wishes.

*) IMHO Adrian for sure would have  indicated (if he had seen a series of consecutive sections, did he?) the existence of gland cells around the periphery of the empty "sacs" shown in the enclosed image. These optically "empty" spaces (only at two tiniest places one has an impression there might have been left some kind of pink stained material adhering to the inner layer) are not lined by definite epi- or even endothelial cell layers one might expect in case of e.g. gland duct(s), or any kind of vasculature (venous, lymphatic):....I don't see in any place a simple circumferential cell layer except not fully circumferential denser red-pink band like structure (which is reminiscent of collagenous strands....or condensed matter comparable to the layers in the basal layer of the epidermis)

As Dr W. Muss said, it looks like that  lipid droplets have probably been lost in the process prior to embedment by the use of xylene, for example. To make sure, try to use a histochemical technique in this same tissue.

I agree that these structures can be channels of glands, though as I mentioned before the reedfish club cells look quite the same and  one has to make quite some sections to see a nucleus. I've seen so large club cells only in reedfish and not in any other fish species. Therefore additional explanation, examples etc will be really helpful.

Best,

Ivan

I think we are not going to solve the "problem" with one single micrograph of one single section;-). A tissue is after all a 3D structure. IF these "spaces" are the terminal parts of gland ducts, Adrian will find these ducts pierce the basal layer somewhere as well as an exit pore. I was thinking of something similar to the ducts of e.g. the sweat glands of humans which have no “own” cellular lining, but are lined by the cells of the epidermis. The glands themselves may be rather deep in the hypodermis. This doesn’t say anything of WHAT the content may be, but Adrian got enough suggestions how to find out;-). Fixation and staining is crucial of course.

Succes!