What do Wolverine, Deadpool and Medusa have in common? All of them have an amazing feature - regeneration. Of course, in comics and movies, this ability, common among a very limited number of real living organisms, is slightly (and sometimes greatly) exaggerated, but it remains quite real. And what is real can be explained, which is what scientists from Tohoku University (Japan) decided to do in their new study. What cellular processes in the body of a jellyfish are associated with regeneration, how does this process proceed, and what other super-powers do these jelly-like creatures have? The report of the research group will tell us about this. Go.
Research basis
First of all, scientists explain why they decided to focus their attention on jellyfish. The fact is that most research in the field of biology is carried out with the participation of so-called model organisms: mice, fruit flies, worms, fish, etc. But there are millions of species on our planet, each of which has one or another unique ability. Therefore, it is impossible to fully evaluate the process of cellular regeneration by studying only one species, and to assume that the studied mechanism will be common to all creatures on Earth.
As for jellyfish, these creatures, by their appearance alone, speak of their uniqueness, which cannot but attract the attention of scientists. Therefore, before proceeding with the dissection of the study itself, I got acquainted with its main character.
The word "jellyfish", which we used to call a creature as such, actually refers only to the stage of the life cycle of the stinger from the subtype medusozoa. Cnidaria got such an unusual name due to the presence of stinging cells (cnidocyte) in their body, which are used for hunting and self-defense. Simply put, when you are stung by a jellyfish, you can thank these cells for the pain and suffering.
Cnidocytes contain cnidocyst, an intracellular organelle responsible for the "stinging" effect. According to their appearance and, accordingly, the method of application, several types of cnidocytes are distinguished, among which we can distinguish:
- penetrants - threads with pointed ends that pierce the body of a victim or offender like spears, injecting a neurotoxin;
- glutinants - sticky and long threads that envelop the victim (not the most pleasant hugs);
- Volvents are short threads in which the victim can easily become entangled.
Such non-standard weapons are explained by the fact that jellyfish, although graceful, are not particularly nimble creatures. The neurotoxin that enters the body of the prey instantly paralyzes it, which gives the jellyfish a lot of time for a lunch break.
Medusa after a successful hunt.
In addition to the unusual method of hunting and defense, jellyfish have a very unusual reproduction. Males produce spermatozoa, and females produce eggs, after the fusion of which planulas (larvae) are formed, settling on the bottom. After a while, a polyp grows out of the larva, from which, upon reaching its maturity, young jellyfish literally break off (in fact, budding occurs). Thus, there are several stages of the life cycle, one of which is the jellyfish or jellyfish generation.
Hairy cyanide, also known as "lion's mane".
If the hairy cyanide were asked how to increase the efficiency of hunting, she would answer - more tentacles. There are about 60 of them in total (clusters of 15 tentacles on each corner of the dome). In addition, this type of jellyfish is considered the largest, because the diameter of the dome can reach 2 meters, and the tentacles during the hunt can stretch up to 20 meters. The good thing is that this species is not particularly βpoisonousβ, therefore it is not fatal to humans.
The sea wasp, in turn, would add quality to the quantity. This species of jellyfish also has 15 tentacles (3 m long) on ββeach of the four corners of the dome, but their poison is many times stronger than that of a large-sized relative. It is believed that the neurotoxin in the body of a sea wasp is enough to kill 60 people in 3 minutes. This thunderstorm lives in the coastal zone of northern Australia and New Zealand. According to data from 1884 to 1996, 63 people died in Australia, but these data may be inaccurate, and the number of fatal encounters between a person and a sea wasp may be much higher. However, according to data for 1991-2004, among 225 cases, only 8% of the victims were hospitalized, among which there was one fatal outcome (a three-year-old child).
Sea wasp
Now back to our study today.
From the point of view of cells, the most important process of the entire life of any organism is cell proliferation - the process of growth of body tissues through the reproduction of cells by division. During the growth of the organism, this process regulates the increase in body size. And when the body is fully formed, the proliferating cells regulate the physiological exchange of cells and the replacement of damaged ones with new ones.
Cnidaria, being a related group of bilateral and early branches of the development of multicellular organisms, have been used to study evolutionary processes for many years. Therefore, cnidarians are no exception in terms of proliferation. For example, during the embryonic development of the sea anemone nematostella vectensis cell proliferation is coordinated with the organization of the epithelium and is involved in the development of tentacles.
nematostella vectensis
Among other things, cnidarians, as we already know, are known for their regenerative abilities. Hydra polyps (a genus of freshwater sessile coelenterates from the hydroid class) have been considered the most popular among researchers for hundreds of years. Proliferation, activated by dying cells, starts the process of regeneration of the basal hydra head. The very name of this creature alludes to a mythical creature known for its regeneration - the Lernean Hydra, which Hercules was able to defeat.
Although regenerative abilities have been linked to proliferation, it remains unclear exactly how this cellular process proceeds under normal conditions at different stages of organism development.
Jellyfish, which have a complex life cycle consisting of two stages of reproduction (vegetative and sexual), serve as an excellent model for studying proliferation.
In this work, the role of the main studied individual was played by the jellyfish of the species Cladonema pacificum. This species lives off the coast of Japan. Initially, this jellyfish has 9 main tentacles, which begin to branch and increase in size (like the whole body) during development to an adult. This feature allows you to study in detail all the mechanisms that are involved in this process.
In addition to the Cladonema pacificum the study also looked at other types of jellyfish: Cytaeis uchidae ΠΈ Rathkea octopunctata.
Results of the study
To understand the spatial pattern of cell proliferation in Cladonema medusa, the scientists used 5-ethynyl-2'-deoxyuridine (EdU) staining, which marks cells in S-phase* or cells that have already passed it.
S-phase* phase of the cell cycle in which DNA replication occurs.
Given that Cladonema increases dramatically in size and exhibits branching of the tentacles during development (1Aβ1C), the distribution of proliferating cells may change throughout maturation.
Image #1: Features of cell proliferation in young Cladonema.
Due to this feature, it was possible to study the mechanism of cell proliferation in both young (day 1) and mature (day 45) jellyfish.
In young jellyfish, EdU-positive cells were found in large numbers throughout the body, including the umbel, manubrium (the supporting organ of the mouth in jellyfish), and tentacles, regardless of the time of EdU exposure (1D-1K ΠΈ 1N-1O, EdU: 20 Β΅M (micromolar) after 24 hours).
Quite a few EdU-positive cells were found in the manubrium (1F ΠΈ 1G), but in the umbrella their distribution was very uniform, especially in the outer shell of the umbrella (exumbrella, 1Hβ1K). In the tentacles, EdU-positive cells were highly clustered (1N). The use of a mitotic marker (PH3 antibody) made it possible to verify that EdU-positive cells are proliferating cells. PH3-positive cells have been found in both the umbrella and the tentacle bulb (1L ΠΈ 1P).
In tentacles, mitotic cells were mainly found in the ectoderm (1P), while in the umbrella proliferating cells were located in the surface layer (1M).
Image #2: Features of cell proliferation in sexually mature Cladonema.
As in juveniles, so in mature individuals, EdU-positive cells were found in large numbers throughout the body. In the umbrella, EdU-positive cells were more often located in the surface layer than in the lower one, which is similar to the observations in juveniles (2Aβ2D).
But in the tentacles, the situation was somewhat different. EdU-positive cells clustered at the base of the tentacle (bulb), where two clusters were found on either side of the bulb (2E ΠΈ 2F). In young individuals, similar clusters were also observed (1N), i.e. the bulbs of the tentacles may be the main zone of proliferation throughout the medusoid stage. Interestingly, in the manubrium of adults, the number of EdU-positive cells was significantly higher than in young ones (2G ΠΈ 2H).
The intermediate result is that cell proliferation can occur uniformly in the umbrella of a jellyfish, and in the tentacles this process is very localized. Therefore, it can be assumed that uniform cell proliferation can control body growth and tissue homeostasis, while clusters of proliferating cells near tentacle bulbs are involved in tentacle morphogenesis.
In terms of the development of the body as such, proliferation plays an important role in the growth of the body.
Image #3: The importance of proliferation in the growth of the body of a jellyfish.
In order to test this in practice, scientists followed the growth of the body of jellyfish, starting with young individuals. It is easiest to determine the size of a jellyfish's body by its dome, since it grows evenly and in direct proportion to the entire body.
Under normal feeding under laboratory conditions, the size of the dome increases sharply by 54.8% during the first 24 hours, from 0.62 Β± 0.02 mm2 to 0.96 Β± 0.02 mm2. During the next 5 days of observations, the size increased slowly and smoothly up to 0.98 Β± 0.03 mm2 (3Πβ3S).
Jellyfish from the other group, which were deprived of food, did not grow, but decreased (red line on the graph 3S). Cellular analysis of starving jellyfish showed the presence of an extremely low number of EdU cells: 1240.6 Β± 214.3 in jellyfish from the control group and 433.6 Β± 133 in starving ones (3Dβ3H). This observation may be direct evidence that nutrition directly influences the proliferation process.
To test this hypothesis, the scientists conducted a pharmacological analysis during which they blocked the progression of the cell cycle using hydroxycarbamide (CH4N2O2), a cell cycle inhibitor that causes G1 arrest. As a result of this intervention, the S-phase cells previously detected using EdU disappeared (3Iβ3L). Thus, jellyfish exposed to CH4N2O2 did not show body growth, unlike the control group (3M).
The next stage of the study was a detailed study of the branching tentacles of jellyfish in order to confirm the assumption that local cell proliferation in the tentacles contributes to their morphogenesis.
Image #4: Effect of local proliferation on the growth and branching of jellyfish tentacles.
The tentacles of a young jellyfish have one branch, but over time their number increases. Under laboratory conditions, branching increased 3 times on the ninth day of observations (4Π ΠΈ 4S).
Again, when using CH4N2O2, branching of the tentacles was not observed, and there was only one branch (4B ΠΈ 4C). Curiously, the removal of CH4N2O2 from the body of jellyfish restored the process of branching of the tentacles, which indicates the reversibility of drug intervention. These observations clearly indicate the importance of proliferation for tentacle development.
Cnidaria would not be cnidarians without nematocytes (cnidocytes, i.e. cnidarians). In the jellyfish species Clytia hemisphaerica, stem cells in the bulbs of the tentacles supply nematocysts to the tips of the tentacles precisely by cell proliferation. Naturally, scientists decided to test this statement.
To detect any association between nematocysts and proliferation, a nuclear stain was used that can mark poly-Ξ³-glutamate synthesized in the nematocyst wall (DAPI, ie 4',6-diamidino-2-phenylindole).
Poly-Ξ³-glutamate staining made it possible to estimate the size of nematocytes, varying from 2 to 110 ΞΌm2 (4Dβ4G). A number of empty nematocysts were also detected, i.e. such nematocytes were depleted (4Dβ4G).
Proliferation activity in jellyfish tentacles was tested by examining voids in nematocytes after blocking the cell cycle with CH4N2O2. The proportion of empty nematocytes in jellyfish after medical intervention was higher than in the control group: 11.4% Β± 2.0% in jellyfish from the control group and 19.7% Β± 2.0% in jellyfish with CH4N2O2 (4Dβ4G ΠΈ 4H). Therefore, even after depletion, nematocytes continue to be actively supplied with proliferation precursor cells, which confirms the influence of this process not only on the development of tentacles, but also on nematogenesis in them.
The most interesting stage was the study of the regenerative abilities of jellyfish. Given the high concentration of proliferative cells in the tentacle bulb in mature jellyfish Cladonema, scientists decided to study the regeneration of the tentacles.
Image #5: Effect of proliferation on tentacle regeneration.
After dissection of the tentacles at the base, a regeneration process was observed (5A-5D). During the first 24 hours, healing occurred in the area of ββthe incision (5B). On the second day of observations, the tip began to lengthen and branching appeared (5S). On the fifth day, the tentacle was fully branched (5D), therefore, tentacle regeneration may follow normal tentacle morphogenesis after elongation.
To better understand the initial stage of regeneration, the scientists analyzed the distribution of proliferating cells using PH3 staining to visualize mitotic cells.
While dividing cells were often observed near the amputated area, mitotic cells were dispersed in uncut tentacled control bulbs (5E ΠΈ 5F).
Quantification of PH3-positive cells present in tentacle bulbs revealed a significant increase in PH3-positive cells in tentacle bulbs in amputees compared to controls (5G). As a conclusion, the initial regenerative processes are accompanied by an active increase in cell proliferation in the tentacle bulbs.
The influence of proliferation on regeneration was verified by blocking the cells with CH4N2O2 after cutting off the tentacle. In the control group, the lengthening of the tentacle after its amputation occurred normally, as expected. However, in the CH4N2O2 group, there was no elongation despite normal wound healing (5H). In other words, healing will occur anyway, but proliferation is necessary for proper regeneration of the tentacle.
Finally, scientists decided to study proliferation in other types of jellyfish, namely in Cytaeis ΠΈ Rathkea.
Image #6: Comparison of proliferation in Cytaeis (left) and Rathkea (right) jellyfish.
Π£ Cytaeis medusa EdU-positive cells were observed in the manubrium, tentacle bulbs, and in the upper part of the umbrella (6Π ΠΈ 6V). Location of identified PH3-positive cells in Cytaeis very similar to Cladonema, however, there are some differences (6C ΠΈ 6D). But at Rathkea EdU-positive and PH3-positive cells were found almost exclusively in the region of the manubrium and tentacle bulbs (6Eβ6H).
It is also curious that proliferating cells were often detected in the kidneys of jellyfish Rathkea (6Eβ6G), which reflects the asexual reproduction of this species.
Given the information obtained, it can be assumed that cell proliferation occurs in tentacle bulbs not only in one species of jellyfish, although there are differences due to the difference in physiology and morphology.
For a more detailed acquaintance with the nuances of the study, I recommend looking at .
Finale
One of my favorite literary characters is Hercule Poirot. The astute detective always paid special attention to small details that seemed unimportant to others. Scientists are a lot like detectives who collect all the evidence they can find in order to answer all the questions of the investigation and figure out the "culprit".
No matter how obvious it may sound, but the regeneration of jellyfish cells is directly related to proliferation - an integral process in the development of cells, tissues and, as a result, the whole organism. A more meticulous study of this comprehensive process will allow a better understanding of the molecular mechanisms that underlie it, which, in turn, will expand not only the range of our knowledge, but also directly affect our lives.
Friday off-top:
The march of the Aurelia jellyfish, disturbed by a predator with the unusual name "fried egg jellyfish", i.e. scrambled egg jellyfish (Planet Earth, voice-over - David Attenborough).
It does not apply to jellyfish, but this deep-sea creature (pelican-shaped largemouth) is not often photographed (the reaction of researchers is simply touching).
Thanks for watching, stay curious and have a great weekend everyone! π
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Source: habr.com