Differential tissue development during embryogenesis and regeneration in an annelid

Abstract

The fragmenting potworm Enchytraeus japonensis (Oligochaeta, Annelida) reproduces asexually by dividing the body into several fragments that then regenerate to complete individuals in 4 -5 days. Such large-scale regeneration, however, occurs only in some invertebrates. To better our understanding of why regeneration is so limited in many animals, despite their ability to undergo embryonic development from the single cell of a fertilized egg, comparisons were made between regeneration and embryonic development of E. japonensis by using two methods: histochemistry for alkaline phosphatase (ALP) and immunohistochemistry with an antibody against acetylated tubulin that visualizes nervous system development. The analyses revealed that both ALP expression patterns and central nervous system development differ between embryogenesis and the regeneration, suggesting that regeneration is not a simple reiteration of embryogenesis but involves different regulatory mechanisms. The study provides a basis for the elucidation of mechanisms that are unique and crucial to regeneration.

Molecular approach to annelid regeneration: cDNA subtraction cloning reveals various novel genes that are upregulated during the large‐scale regeneration of the oligochaete, Enchytraeus japonensis

“…3). The data revealed that the expression levels of all of these genes were highest in the regenerating fragments at around 12-24 hr after amputation, i.e., at the blastema formation stage (Myohara et al, 1999;Myohara, 2004) (see the top panels of Fig. 1A).…”

“…As epimorphic regeneration involves certain unique processes, such as wound healing and blastema formation, neither of which are involved in embryogenesis, it is most likely that regeneration requires the activation of unique genes that have not yet been identified in the course of previous developmental studies. In fact, comparisons between regeneration and embryogenesis of E. japonensis have indicated that regeneration is not a simple reiteration of embryonic development, but involves different regulatory mechanisms (Myohara, 2004). Thus, as an initial strategy towards the elucidation of the molecular mechanism of annelid regeneration, we performed suppression subtractive hybridization (Diatchenko et al, 1996) using cDNAs that were derived from regenerating fragments of E. japonensis and from the intact animals.…”

“…The worms were reared at 24°C in 1.1% (w/v) plain agar medium in disposable Petri dishes, and were fed with powdered rolled oats as previously described (Myohara, 2004). Under these conditions, E. japonensis grows continuously to about 10 mm long, consisting of 50 -60 segments, and reproduces asexually by fragmentation every two weeks.…”

The dynamics of alkaline phosphatase activity during operculum regeneration in the polychaete Pomatoceros lamarckii

“…Invertebrate alkaline phosphatases appear to have a similar association with transport: ALP activity has been reported in excretory organs of insects and annelids, salivary glands of insect larvae, and the guts of diverse species (Myohara, 2004;Eguchi, 1995;Hasse et al, 2010;Kitamura and Shimizu, 2000).…”

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

“…Moreover, it is possible to induce sexual reproduction by changing the culture condition. This enables research into embryonic development complementary to the study of regeneration (Myohara, 2004). Compared to hydras and planarians, which have been widely used in research into the regeneration of invertebrates, Annelida Oligochaeta is a more advanced triploblastic animal, as it has a well-developed ladder-like central nervous system, a closed blood-vascular system, a highly developed endocrine system, a coelom, and segmentation.…”