Bipolar head regeneration induced by artificial amputation inEnchytraeus japonensis (Annelida, Oligochaeta)

Abstract

The Enchytraeida Oligochaeta Enchytraeus japonensis propagates asexually by spontaneous autotomy. Normally, each of the 5-10 fragments derived from a single worm regenerates a head anteriorly and a tail posteriorly. Occasionally, however, a head is formed posteriorly in addition to the normal anterior head, resulting in a bipolar worm. This phenomenon prompted us to conduct a series of experiments to clarify how the head and the tail are determined during regeneration in this species. The results showed that (1) bipolar head regeneration occurred only after artificial amputation, and not by spontaneous autotomy, (2) anesthesia before amputation raised the frequency of bipolar head regeneration, and (3) an extraordinarily high proportion of artificially amputated head fragments regenerated posterior heads. Close microscopic observation of body segments showed that each trunk segment has one specific autotomic position, while the head segments anterior to the VIIth segment do not. Only the most posterior segment VII in the head has an autotomic position. Examination just after amputation found that the artificial cutting plane did not correspond to the normal autotomic position in most cases. As time passed, however, the proportion of worms whose cutting planes corresponded to the autotomic position increased. It was suspected that the fragments autotomized after the artificial amputation (corrective autotomy). This post-amputation autotomy was probably inhibited by anesthesia. The rate at which amputated fragments did not autotomize corresponded roughly to the rate of bipolar regeneration. It was hypothesized then that the head regenerated posteriorly if a fragment was not amputated at the precise autotomic position from which it regenerated without succeeding in corrective autotomy.

Re-membering the body: applications of computational neuroscience to the top-down control of regeneration of limbs and other complex organs

“…Specifically: (1) the development of improved methods for reading/writing bioelectrical state information into somatic tissues and sculpting non-neural bioelectric circuits (advances in optogenetics beyond excitable cells and in the synthetic biology of gap junction and neurotransmitter signaling) 32d , (2) continued work on cracking the bioelectric code (understanding how bioelectric state information maps onto the topology of various patterning outcomes in tractable model systems such as planaria) 16a , (3) formulation and testing of quantitative, molecular models of LTP, habituation, sensitization, and synaptic plasticity applied to slow bioelectric signaling in non-neural cell groups regulating regenerative growth 96b , (4) use of reagents that impact cognition (hallucinogens, anesthetics 131 , stimulants, nootropics/cognitive enhancers, etc.) in developmental and regenerative patterning assays to probe conservation of pathways between neuroscience and morphogenesis, (5) in silico study and synthetic implementation of biophysics models of circuits which can stably store bioelectric state information as attractor states of ion channel activity in arbitrary cell types 132 , (6) creation of larger-scale computational models of regeneration and functional experiments in morphogenesis based on goal-seeking and error minimization algorithms with molecularly-specified metrics 133 , (7) exploration of molecular models of cognitive concepts (attention, autism spectrum, sleep, visual illusions/hallucinations, addiction) in specific patterning and mispatterning contexts, (8) experimental examination of learning and complex behavior 134 in non-neural in vitro constructs to understand the cognitive powers of non-excitable cell networks 135 , (9) bioengineering platforms that reward and punish in vitro patterning systems for specific changes in growth and morphogenesis (seeking to demonstrate instrumental learning and top-down control of shape in developmental or regenerative contexts), and (10) a mechanistic investigation of the mechanism of persistence of memories through massive brain regeneration, which is likely to reveal the interface between somatic and neural memories 136 .…”

Stem cell system in asexual and sexual reproduction of Enchytraeus japonensis (Oligochaeta, Annelida)

“…2000). Decapitated worms placed on agar plates autotomize within 24 h. Fragments can also be obtained artificially by cutting with a surgical blade (amputation) or by electrical stimulus (Christensen 1964; Kawamoto et al. 2005).…”

“…During the fragmentation process, the circular body wall muscles contract near one of these neuromuscular junctions in the middle of the segment (fission zone), which causes constriction and results in fission of the body (Yoshida‐Noro et al. 2000; Kawamoto et al. 2005).…”

“…2000). In addition, we failed to obtain autotomy in decapitated or electrically stimulated worms that were anesthetized (Kawamoto et al. 2005).…”

Functional analysis of grimp, a novel gene required for mesodermal cell proliferation at an initial stage of regeneration in Enchytraeus japonensis (Enchytraeidae, Oligochaete)

“…An enchytraeid worm Enchytraeus japonensis has been cultured asexually in our laboratory as described previously (Kawamoto et al, 2005). All fragments were cut artificially using a disposable surgical blade to contain about 10 segments.…”