Abstract
BackgroundProseriates (Proseriata, Platyhelminthes) are free-living, mostly marine, flatworms measuring at most a few millimetres. In common with many flatworms, they are known to be capable of regeneration; however, few studies have been done on the details of regeneration in proseriates, and none cover cellular dynamics. We have tested the regeneration capacity of the proseriate Monocelis sp. by pre-pharyngeal amputation and provide the first comprehensive picture of the F-actin musculature, serotonergic nervous system and proliferating cells (S-phase in pulse and pulse-chase experiments and mitoses) in control animals and in regenerates.ResultsF-actin staining revealed a strong body wall, pharynx and dorsoventral musculature, while labelling of the serotonergic nervous system showed an orthogonal pattern and a well developed subepidermal plexus. Proliferating cells were distributed in two broad lateral bands along the anteroposterior axis and their anterior extension was delimited by the brain. No proliferating cells were detected in the pharynx or epidermis.Monocelis sp. was able to regenerate the pharynx and adhesive organs at the tip of the tail plate within 2 or 3 days of amputation, and genital organs within 8 to 10 days. Posterior pieces were not able to regenerate a head.The posterior regeneration blastema was found to be a centre of cell proliferation, whereas within the pharynx primordium, little or no proliferation was detected. The pharynx regenerated outside of the blastema and was largely, but not solely formed by cells that were proliferating at the time of amputation.ConclusionsOur findings suggest that proliferating cells or their offspring migrated to the place of organ differentiation and then stopped proliferating at that site. This mode of rebuilding organs resembles the mode of regeneration of the genital organs in another flatworm, Macrostomum lignano. Pharynx regeneration resembles embryonic development in Monocelis fusca and hints at the vertically directed pharynx being plesiomorphic in proseriates.Proliferation within the regeneration blastema has been detected in anterior and posterior blastemas of other flatworms, but is notably missing in triclads. The phylogenetic relationships of the flatworms studied indicate that proliferation within the blastema is the plesiomorphic condition in Platyhelminthes.Electronic supplementary materialThe online version of this article (doi:10.1186/2041-9139-5-37) contains supplementary material, which is available to authorized users.
Highlights
Proseriates (Proseriata, Platyhelminthes) are free-living, mostly marine, flatworms measuring at most a few millimetres
Phylogenetic analysis Our phylogenetic tree based on 18S and 28S ribosomal RNA genes suggests a close relationship between the Monocelis species from the present study and Monocelis lineata, followed by Monocelis fusca and Monocelis longistyla (Additional file 2)
Intact animals To provide a baseline for the regeneration studies, we first investigated the general anatomy of intact Monocelis sp. with a focus on the musculature, the nervous system and proliferating cells
Summary
Proseriates (Proseriata, Platyhelminthes) are free-living, mostly marine, flatworms measuring at most a few millimetres. Proseriates represents a species-rich (over 400 species have been described), widespread, and predominantly marine group of hermaphroditic free-living flatworms (Platyhelminthes) [1] It is split into the Unguiphora (without a statocyst) and the Lithophora Apart from triclads, other taxa of the free-living flatworms are known to regenerate, to different extents [7] Many of these flatworm groups are understudied and lack the application of more contemporary methods, such as visualization of their stem cell system by 5-bromo-2′-deoxyuridine (BrdU) labelling, which could provide comparative insights into the regeneration processes of free-living flatworms. This lack of information holds true for flatworms of the order Proseriata, in which the most recent overview of their powers of regeneration was published almost 50 years ago [8]
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