Abstract
Planarians are bilaterally symmetric metazoans of the phylum Platyhelminthes. They have well-defined anteroposterior and dorsoventral axes and have a highly structured true brain which consists of all neural cell types and neuropeptides found in a vertebrate. Planarian flatworms are famous for their strong regenerative ability; they can easily regenerate any part of the body including the complete neoformation of a functional brain within a few days and can survive a series of extreme environmental stress. Nowadays, they are an emerging model system in the field of developmental, regenerative, and stem cell biology and have offered lots of helpful information for these realms. In this review, we will summarize the response of planarians to some typical environmental stress and hope to shed light on basic mechanisms of how organisms interact with extreme environmental stress and survive it, such as altered gravity, temperature, and oxygen, and this information will help researchers improve the design in future studies.
Highlights
Planarians are bilaterally symmetric metazoans of the phylum Platyhelminthes. They have well-defined anteroposterior and dorsoventral axes and have an anterior cephalic region which contains the brain and a pair of eyespots, a central region which includes the pharynx and the mouth, and a posterior tail region. Despite their relatively simple morphology, planarians have a highly structured central nervous system (CNS) and feature a true brain which consists of all neural cell types and neuropeptides found in vertebrates [1,2,3]
In space-exposed worms, the number of colonies of Variovorax, Herminiimonas, and the unknown Comamonadaceae decreased and the number of Chryseobacterium colonies significantly increased. Their results indicate that space travel can change bacterial community composition of D. japonica, and this difference can exist for a few years. They analyzed the samples of the water of the space-exposed worms and the Earth-only with liquid chromatographymass spectrometry (LC-MS); the results revealed that both samples contained a large number of small organic molecules/metabolites
Tsushima et al found that the protein of DJ-1 is conversed from human to planarian, especially the important residues for function execution; they knock down the DJ-1 gene in vivo through RNAi, and the results showed that planarian DJ-1 has antioxidant and neuroprotective functions; it indicates that planarian can be a reliable model for study oxidative stress-introduced disorders and offer the chance to explore the mechanisms [53]
Summary
They have well-defined anteroposterior and dorsoventral axes and have an anterior cephalic region which contains the brain and a pair of eyespots, a central region which includes the pharynx and the mouth, and a posterior tail region Despite their relatively simple morphology, planarians have a highly structured central nervous system (CNS) and feature a true brain which consists of all neural cell types and neuropeptides found in vertebrates [1,2,3]. The bad news is that astronauts on a long-term mission have problems upon returning to Earth, such as bone density loss; muscle atrophy; cardiovascular and hematic changes; metabolic, endocrine, and sleep disturbances; and rapid senescence [11, 12] These actual and potential physical effects on the body mainly come from extreme environmental stress outside the Earth, such as altered gravity, temperature, and oxygen. This information will help researchers understand the basic mechanisms and improve the design in future studies
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