Regeneration: Organizing the Blastema in Planarians

Theoretical insights, degradation, and sub-lethal toxicity of thiamethoxam to the planarian Girardia tigrina

Advanced oxidative processes, such as Photo-Fenton, transform organic contaminants due to the attack by radicals. In this context, the lethal and sub-lethal effects of the Cruiser® 350FS (CRZ) with the active ingredient thiamethoxam (TMX) were investigated using the planarian Girardia tigrina. Degradation of thiamethoxam by the Fenton process was also assessed by using theoretical studies and the efficiency of Solar-Fenton versus Fenton. The 48 h LC50 value of CRZ for planarians was 478.6 mg L-1. The regeneration of planarians was significantly affected for concentrations ≥ 17 mg·L-1 of TMX (24 h). The Solar-Fenton showed a high degradation percentage reaching ~70%. The theoretical model showed the atoms of the TMX molecule that will suffer attacks from the formed radicals. Current results open new perspectives concerning the treatment of TMX in the aquatic environment because the 70% degradation seems to be sufficient to reach concentrations that do not induce sub-lethal effects in planarians. Further studies should determine if the by-products generated might be toxic for planaria or other organisms.

Cadmium sulfate induces apoptosis in planarians

With rapid socio-economic development, heavy metal pollution in water has become common and affects both environment and human health. Cadmium (Cd) has been recognized as one of the heavy metals which cause acute or chronic toxic effects if ingested. Although its toxicity is undisputed, the underlying molecular mechanisms in vivo are not fully understood. Planarians, a model organism famous for their regenerative prowess, have long been utilized to study the effects of chemical exposure. In this study, we observed apoptosis with TUNEL assay in planarians induced by cadmium sulfate (CdSO₄) in a dose-dependent manner. The apoptosis-related genes were detected with quantitative RT-PCR. Significant changes in c-Myc, P53, and BcL-2 were indicated, which may play a partial role in the regulation of the process of apoptosis in the planarians. H&E staining showed that Cd had obvious biological toxicity in the planarians. Here, new insights on metal toxicity mechanisms are provided, contributing to understand how CdSO₄ induces the pathological and physiological processes of apoptosis in the living bodies. Meanwhile, planarians are proved to be a freshwater pollution indicator and toxicological research model.

Autophagic dedifferentiation induced by cooperation between TOR inhibitor and retinoic acid signals in budding tunicates

Asexual bud development in the budding tunicate Polyandrocarpa misakiensis involves transdifferentiation of multipotent epithelial cells, which is triggered by retinoic acid (RA), and thrives under starvation after bud isolation from the parent. This study aimed to determine cell and molecular mechanisms of dedifferentiation that occur during the early stage of transdifferentiation. During dedifferentiation, the numbers of autophagosomes, lysosomes, and secondary lysosomes increased remarkably. Mitochondrial degradation and exosome discharge also occurred in the atrial epithelium. Autophagy-related gene 7 (Atg7) and lysosomal proton pump A gene (PumpA) were activated during the dedifferentiation stage. When target of rapamycin (TOR) inhibitor was administered to growing buds without isolating them from the parent, phagosomes and secondary lysosomes became prominent. TOR inhibitor induced Atg7 only in the presence of RA. In contrast, when growing buds were treated with RA, lysosomes, secondary lysosomes, and mitochondrial degradation were prematurely induced. RA significantly activated PumpA in a retinoid X receptor-dependent manner. Our results indicate that in P. misakiensis, TOR inhibition and RA signals act in synergy to accomplish cytoplasmic clearance for dedifferentiation.