Abstract
Trichoplax adhaerens is the simplest multicellular animal with tissue differentiation and somatic cell turnover. Like all other multicellular organisms, it should be vulnerable to cancer, yet there have been no reports of cancer in T. adhaerens or any other placozoan. We investigated the cancer resistance of T. adhaerens, discovering that they are able to tolerate high levels of radiation damage (218.6 Gy). To investigate how T. adhaerens survive levels of radiation that are lethal to other animals, we examined gene expression after the X-ray exposure, finding overexpression of genes involved in DNA repair and apoptosis including the MDM2 gene. We also discovered that T. adhaerens extrudes clusters of inviable cells after X-ray exposure. T. adhaerens is a valuable model organism for studying the molecular, genetic, and tissue-level mechanisms underlying cancer suppression.
Highlights
MethodsLab culturesWe grew T. adhaerens [47] in glass Petri dishes 100 mm diameter × 20 mm high in 30 ml of artificial seawater (ASW) made in the laboratory by adding 32.5 grams of Instant Ocean sea salt (Prod. n. 77 SS15-10) per liter of distilled water (pH 8), at constant and controlled temperature (23 ̊C) and humidity (60%) with a photoperiod of 14 hours/10 hours light/dark cycle in an environmental chamber (Thermo Fisher Scientific, mod. 3940)
We found that T. adhaerens are able to tolerate high levels of radiation and are resilient to DNA damage
We found that radiation exposure induced the overexpression of genes involved in DNA repair and apoptosis
Summary
Lab culturesWe grew T. adhaerens [47] in glass Petri dishes 100 mm diameter × 20 mm high in 30 ml of artificial seawater (ASW) made in the laboratory by adding 32.5 grams of Instant Ocean sea salt (Prod. n. 77 SS15-10) per liter of distilled water (pH 8), at constant and controlled temperature (23 ̊C) and humidity (60%) with a photoperiod of 14 hours/10 hours light/dark cycle in an environmental chamber (Thermo Fisher Scientific, mod. 3940). We grew T. adhaerens [47] in glass Petri dishes 100 mm diameter × 20 mm high in 30 ml of artificial seawater (ASW) made in the laboratory by adding 32.5 grams of Instant Ocean sea salt We fed T. adhaerens with diatom algae (Pyrenomonas helgolandii) ab libitum. Each plate can contain hundreds of animals. When their numbers increase and when food is depleted, T. adhaerens detach from the plate surface and float on the water’s surface. We gently collected the floating T. adhaerens with a loop and transferred them to new plates, along with 3 ml of ASW from the old plate. This step is required for the animals to successfully grow in the new plates. The animal and algae cultures are assembled in a sterile environment using a biological hood and using sterile materials so that the cultures are protected from parasites and other microorganisms that might interfere with the maintenance of healthy cultures and experiments
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