Abstract
Regeneration of body parts and their interaction with the immune response is a poorly understood aspect of earthworm biology. Consequently, we aimed to study the mechanisms of innate immunity during regeneration in Eisenia andrei earthworms. In the course of anterior and posterior regeneration, we documented the kinetical aspects of segment restoration by histochemistry. Cell proliferation peaked at two weeks and remitted by four weeks in regenerating earthworms. Apoptotic cells were present throughout the cell renewal period. Distinct immune cell (e.g., coelomocyte) subsets were accumulated in the newly-formed blastema in the close proximity of the apoptotic area. Regenerating earthworms have decreased pattern recognition receptors (PRRs) (e.g., TLR, except for scavenger receptor) and antimicrobial peptides (AMPs) (e.g., lysenin) mRNA patterns compared to intact earthworms. In contrast, at the protein level, mirroring regulation of lysenins became evident. Experimental coelomocyte depletion caused significantly impaired cell divisions and blastema formation during anterior and posterior regeneration. These obtained novel data allow us to gain insight into the intricate interactions of regeneration and invertebrate innate immunity.
Highlights
The regeneration capacity is a poorly understood aspect of biology and explaining its variation among animals remains elusive [1]
The role of the immune system is crucial in the regeneration process and to the best of our knowledge, the regeneration capacity is inversely proportional to the development of the immune system
Several cellular and molecular alterations of innate immunity were observed in regenerating E. andrei earthworms
Summary
The regeneration capacity is a poorly understood aspect of biology and explaining its variation among animals remains elusive [1]. The extensive regeneration ability initially flourished at the dawn of animal evolution presumably coinciding with the origin of multicellularity; limitations or loss of regeneration capability have been widespread across the phylogenesis [2]. It is hypothesized that in higher developed vertebrates’ the regeneration of whole organs and body parts is hampered by the evolution of the adaptive immune system that determines only wound-healing and scarring following the tissue injury. In this light, the transition into warm-blooded vertebrates required prompt responses instead of whole-body part or organ regeneration [2,3,4,5,6,7]
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