by Jeya Chelliah B.Vsc Ph.D
Placozoans, at first glance, might be mistaken for simple amoebas under the microscope. However, these seemingly basic creatures are genuine animals, more closely related to cnidarians like sea anemones and vertebrate-inclusive bilaterians than to ctenophores or poriferans. Their body structure, reminiscent of a sandwich, boasts a distinct top-bottom polarity and houses at least nine differentiated somatic cell types. This includes upper and lower epithelial cells, fiber cells, and three types of gland cells, with more yet to be described. Their locomotion, facilitated by interconnected fiber cells, occasionally pauses for extracellular digestion of food particles.
One of the most captivating attributes of placozoans is their exceptional regenerative abilities. Any partial mechanical disruptions in their body can heal within minutes. Furthermore, while many animals have neuron-driven nervous systems, placozoans rely on peptidergic cells. These cells release short amino acid chains that activate surrounding cells, hinting at the evolution of early nervous systems as cell networks connected through chemical signals.
The Phylum Placozoa comprises only two species: Treptoplax reptans and Trichoplax adhaerens. The latter, discovered on an Australian marine aquarium’s walls in 1883, is found in tropical and subtropical marine waters globally. These organisms have differentiated dorsal and ventral epithelial cell layers enclosing a mesenchymal syncytial net. They move via gliding, aided by ciliated cells, and feed by engulfing organic detritus particles. Placozoans reproduce both asexually and sexually, with environmental factors like water temperature influencing the mode of reproduction.
In recent times, Trichoplax adhaerens has garnered attention for its remarkable properties. This marine-dwelling creature can tolerate high radiation doses that would be lethal to most life forms. More intriguingly, T. adhaerens exhibits a unique ability to resist cancer. Through aggressive DNA repair and damaged cell ejection, this organism engages in continual bodily renewal, remaining cancer-free. This discovery has profound implications for understanding natural cancer suppression mechanisms. Given that T. adhaerens can withstand radiation doses up to 218.6 Gy (compared to the 3-7 Gy that damages mammalian cells), it offers a promising model for studying radiation tolerance and DNA repair mechanisms.
However, it’s essential to approach these findings with caution. While the cancer suppression mechanism in T. adhaerens is fascinating, it could have adverse effects in humans if mutated cells are extruded into the bloodstream and migrate elsewhere.
In conclusion, placozoans, particularly T. adhaerens, present a promising avenue for cancer research. Their unique characteristics, combined with their simplicity, make them invaluable for understanding fundamental regeneration processes and potential applications in medical research. As we delve deeper into the mysteries of these microscopic wonders, their potential role in shaping the future of cancer research becomes increasingly evident.