Freshwater Annelids Research Articles

Investment in regeneration versus asexual reproduction is resource‐dependent in a freshwater annelid

Abstract The post‐embryonic developmental processes of regeneration and asexual agametic reproduction are widespread and often co‐occur in animals. These traits are of great ecological significance, but their physiological dynamics within species are not well understood. In naid annelids, regeneration and asexual reproduction via fission are evolutionarily related and mechanistically similar yet distinct, making these animals useful systems in which to study resource allocation strategies between the two processes. How asexual reproductive investment varies as a function of somatic investment demands was tested in the naid Pristina leidyi by repeatedly amputating the heads of individual worms, allowing regeneration to proceed, and measuring reproductive output over time. Treatments were replicated under high and low food levels to determine to what extent the investment dynamic between regeneration and fission is affected by the resource pool. Reproductive output was affected by injury and regeneration frequency in a resource‐dependent manner, such that only worms with less food availability exhibited reproductive deficits; injury and regeneration did not affect reproductive output of worms under the high food condition. When reproductive output was decreased, this occurred not through a reduction in offspring quantity but a reduction in offspring quality. In the offspring of experimental animals, body size and fission speed were dependent on parental feeding level and to a lesser and inconsistent extent on parental injury history, but regeneration speed was unaffected by parental treatment. These findings suggest that, in a species capable of both regeneration and asexual reproduction: (1) the resource pool is a key factor mediating the resource investment pattern between regeneration and fission; (2) sacrificing per‐offspring investment rather than fecundity may be an optimal strategy if resources are limiting; (3) regeneration and fission have evolved distinct resource allocation pathways. This work prompts further questions about the physiological dynamics between regeneration and asexual reproduction in animals, such as whether and to what extent these have evolved adaptively, including in response to injury and resource pressures. Read the free Plain Language Summary for this article on the Journal blog.

Characterization of novel aurantiactinomyxon types (Cnidaria, Myxosporea) from the oligochaete Ilyodrilus templetoni (Southern, 1909), with a comprehensive phylogeny of the collective group

Three new aurantiactinomyxon types are described from the oligochaete Ilyodrilus templetoni (Southern, 1909) (Naididae) collected from a northern Portuguese estuary, based on light microscopy and sequencing of the 18S rDNA. The addition of I. templetoni to the group of freshwater annelids known to be permissive for aurantiactinomyxon development reinforces the crucial role of naidids in the evolution and settlement of myxozoans in estuarine environments. Maximum likelihood and Bayesian inference analyses of a comprehensive 18S rDNA dataset placed the novel types within the Paramyxidium clade. This positioning suggests them as probable life cycle counterparts to Paramyxidium spp. that most likely infect the European eel Anguilla anguilla, as the sole representative of Elopomorpha in Portuguese rivers. Although distance estimation revealed a genetic difference of only 0.4 % between Aurantiactinomyxon types 1 and 3, this value was determined to be representative of interspecific variability based on the consistent matching of both genotypes with distinct actinospore morphologies, and potential richness of closely related species of Paramyxidium infecting the European eel in Portuguese waters. The clustering of aurantiactinomyxon types within distinct myxosporean lineages, representative of the suborders Variisporina and Platysporina, demonstrates that the aurantiactinomyxon morphotype is highly functional in promoting myxozoan infections in estuarine environments.

Toxicity of environmentally relevant concentration of PFAS chemicals in Lumbriculus variegatus (Oligochaeta, Lumbriculidae) – A multi-bioindicator study

PFAS, or per- and polyfluoroalkyl substances, are a family of man-made chemicals found in a variety of products from non-stick cookware and food wrappers to firefighting foams. PFAS are persistent and widely distributed in the environment, including aquatic environments. In this study we examined the impact of PFAS chemicals on the physiological and behavioral endpoints of Lumbriculus variegatus (i.e., blackworms). Lumbriculus variegatus is a species of freshwater annelid worm that plays key roles in shallow freshwater ecosystems. At an environmentally relevant concentration of 1 μg/L, 12-day aqueous exposure to long chain PFAS, including PFOA, PFOS and PFDA, each markedly slowed the pulse rate of the dorsal blood vessel in L. variegatus, indicating a suppressive effect on blood circulation. The mean pulse rate was reduced from 9.6 beats/minute to 6.2 and 7.0 beats/min in PFOA and PFOS, respectively (P < 0.0001). Further, PFOA, PFOS and PFDA reduced the escape responsiveness of L. variegatus to physical stimulation. The percentage of worms showing normal escape behavior was reduced from 99.0% in control to 90.6% in the PFOS exposed group (P < 0.01). In a chronic (4 week) growth study, exposure to overlying water and sediment spiked with PFOA, PFOS or PFDA reduced the total biomass and the number of worms, indicating a suppressive effect on worm population growth. For instance, PFOA and PFDA reduced the total dry biomass by 26.3% and 28.5%, respectively, compared to the control (P < 0.05). The impact of PFAS on blackworm physiology is accompanied by an increase in lipid peroxidation. The level of malondialdehyde (MDA), an indicator of lipid peroxidation, and catalase, a major antioxidant enzyme, were markedly increased in PFOA, PFOS and PFDA exposed groups. Interestingly, exposure to PFHxA, a short chain PFAS, had no detectable effect on any of the measured endpoints. Our results demonstrate that L. variegatus is highly sensitive to the toxic impact of long chain PFAS chemicals as measured by multiple endpoints including blood circulation, behavior, and population growth. Such toxicity may have a detrimental impact on L. variegatus and the freshwater ecosystems where it resides.

Cryptic carnivores: Intercontinental sampling reveals extensive novel diversity in a genus of freshwater annelids

Freshwater annelids are globally widespread in aquatic ecosystems, but their diversity is severely underestimated. Obvious morphological features to define taxa are sparse, and molecular phylogenetic analyses regularly discover cryptic diversity within taxa. Despite considerable phylogenetic work on certain clades, many groups of freshwater annelids remain poorly understood. Included among these are water nymph worms of the genus Chaetogaster (Clitellata: Tubificida: Naididae: Naidinae). These worms have diverged from the detritivorous diet of most oligochaetes to become more predatory and exist as omnivores, generalist predators, parasites, or symbionts on other invertebrates. Despite their unusual trophic ecology, the true diversity of Chaetogaster and the phylogenetic relationships within the genus are uncertain. Only three species are commonly referenced in the literature (Chaetogaster diaphanus, Chaetogaster limnaei, and Chaetogaster diastrophus), but additional species have been described and prior molecular data suggests that there is cryptic diversity within named species. To clarify the phylogenetic diversity of Chaetogaster, we generated the first molecular phylogeny of the genus using mitochondrial and nuclear sequence data from 128 worms collected primarily across North America and Europe. Our phylogenetic analyses suggest that the three commonly referenced species are a complex of 24 mostly cryptic species. In our dataset, Chaetogaster “diaphanus” is represented by two species, C. “limnaei” is represented by three species, and C. “diastrophus” is represented by 19 species. North American and European sequences are largely interspersed across the phylogeny, with four pairs of clades involving distinct North American and European sister groupings. Overall, our study demonstrates that the species diversity of Chaetogaster has been underestimated and that carnivory has evolved at least twice in the genus. Chaetogaster is being used as a model for symbiotic evolution and the loss of regenerative ability, and our study indicates that researchers must be careful to identify which species of Chaetogaster they are working with in future studies.

Journey beyond the embryo: The beauty of Pristina and naidine annelids for studying regeneration and agametic reproduction.

Regeneration, asexual agametic reproduction, and other forms of postembryonic development are ecologically important and widely variable across animals, yet our understanding of this important aspect of animal diversity remains limited. A significant limitation has been the dearth of adequate study systems for exploring the mechanisms and evolution of these processes. Here I describe key parts of our journey in developing naid annelids as a study system for investigating the evolution and development of regeneration and fission. Naids are small freshwater annelids that provide numerous advantages for studying postembryonic development: they are small and reproduce readily by fission, they include species with diverse regenerative abilities, and many species are easy to culture. Among the naids, Pristina leidyi is a particularly useful study species, being largely transparent and quite robust to a variety of experimental manipulations. Building on a sparse but long history of past research on these animals, we have developed this system by establishing methods and generating resources for working with them. Naids are yielding novel insights into the evolution of regeneration and fission, providing one of many examples of the value of developing new study species to enable the exploration of fundamental and understudied questions in biology. Establishing new study systems comes with challenges but is exciting and rewarding, and I provide perspectives from my own experiences with the hope of encouraging the further expansion of study systems in biology.

Studying Annelida Regeneration in a Novel Model Organism: The Freshwater Aeolosoma viride.

Aeolosoma viride, a globally distributed freshwater annelid, has a semitransparent appearance with 10 to 12 segments, about 2 to 3mm in length. It is easy to raise and handle in laboratory conditions. Due to its robust regenerative capacity and applicability of various molecular tools including EdU labeling, whole-mount in situ hybridization (WISH), and RNA interference (RNAi), it rises as a promising model for studying whole-body regeneration.

Molecular taxonomy and description of a new species of Limnodrilus (Naididae, Clitellata, Annelida) in China.

The freshwater annelid worm genus Limnodrilus, including the widely distributed L. claparedianus Ratzel, 1868, is common in Chinese freshwater ecosystems. One species, previously recognized as morphologically intermediate between L. claparedianus and the North American taxon L. cervix Brinkhurst, 1963, is here described as a new species, L. paraclaparedianus Zhou Cui n. sp., using both molecular and traditional taxonomy. Comparisons of sequences of the Cytochrome Oxidase subunit I (COI) mtDNA in a sample of Limnodrilus species showed that the distances between species were generally higher than the divergences within them. Phylogenetic analysis of COI as well as 16S mtDNA and Internal Transcribed Spacer 2 (ITS2) nDNA confirmed that the new species is an independent lineage. Moreover, morphological differences in the prostomium, characteristics of the chaetae and internal genitalia support the separation of the species.

Reducing River Flows to Control a Parasitic Salmonid Disease in the Klamath River: Simulations Question the Efficacy of Desiccation as a Management Tool

AbstractAquatic parasites cause disease in economically and culturally important Klamath River salmonids Oncorhynchus spp., and the myxozoan parasite Ceratonova shasta has been linked to high juvenile salmonid mortality. Because C. shasta requires the freshwater annelid Manayunkia occidentalis to complete its life cycle, management approaches have focused on disrupting annelid populations to reduce C. shasta and disease risk for salmonids. Previous studies have demonstrated that manipulating river discharge to achieve short‐term, high‐flow events is effective for disturbing annelids. There is also interest in the efficacy of manipulating river discharge to desiccate annelids to reduce disease risk. To investigate the efficacy of reducing streamflow to desiccate annelids, we simulated the amount of annelid habitat, categorized by quality, that would be dewatered as discharge was incrementally reduced. Simulations were accomplished by coupling two‐dimensional hydrodynamic models with an annelid presence/absence model. Simulations were conducted for three study sites located on the Klamath River main stem downstream of Iron Gate Dam, where discharge can be manipulated. Reductions in discharge from June base flow (31.2 m3/s or 1,100 ft3/s) to the lowest simulated discharge rate (17.0 m3/s; approximately half of base flow) resulted in an 11.8% reduction of the total wetted area of the river across all three study sites combined. For the same discharge simulation, reductions in annelid habitat differed based on the quality of habitat, with low‐ quality (&lt;0.20 probability of annelids) to moderate‐quality (0.20–0.80 probability of annelids) habitat reduced by 8.3% (95% credible interval = 7.5–10.3) and 23.7% (10.7–27.5), respectively, while high‐quality habitat (&gt;0.80 probability of annelids) was never desiccated. These results suggest that desiccation is unlikely to offer an effective solution for managing myxozoan parasites of salmonids that are transmitted by annelids because reducing streamflow had minimal effects on the amount of annelid habitat.

Caspase dependent apoptosis is required for anterior regeneration in Aeolosoma viride and its related gene expressions are regulated by the Wnt signaling pathway

Although apoptosis has been widely observed during the regenerative process, the mechanisms by which it is regulated and its roles in regeneration remained unclear. In this study, we introduced Aeolosoma viride, a fresh water annelid with an extraordinary regenerative ability as our model organism to study the functions and regulations of apoptotic caspases. Here we showed that major events of apoptosis were detected near the wounded area and showed spatial correlation with the expression patterns of caspase gene namely Avi-caspase X and two apoptosis regulators namely Avi-Bax and Avi-Bcl-xL. Next, we investigated how Avi-caspase X gene expression and apoptosis influence regeneration following head amputation. RNA interference of Avi-caspase X reduced the amounts of apoptotic cells, as well as the percentage of successful regeneration, suggesting a critical role for apoptosis in anterior regeneration of A. viride. In addition, we also discovered that the expression of apoptotic caspases was regulated by the canonical Wnt signaling pathway. Together, our study showed that caspase dependent apoptosis was critical to the anterior regeneration of A. viride, and could be regulated by the canonical Wnt signaling pathway.

The invertebrate host of salmonid fish parasites Ceratonova shasta andParvicapsula minibicornis (Cnidaria: Myxozoa), is a novel fabriciid annelid, Manayunkia occidentalis sp. nov. (Sabellida: Fabriciidae).

Myxosporea (Cnidaria: Myxozoa) are common fish parasites with complex life cycles that involve annelid hosts. Two economically important salmonid-infecting myxosporeans from rivers of the northwestern United States, Ceratonova shasta (Noble, 1950) and Parvicapsula minibicornis Kent et al., 1997, have life cycles that require a freshwater annelid host, identified previously as Manayunkia speciosa Leidy, 1859. This species was described originally from Pennsylvania, with subsequent records from New Jersey, the Great Lakes and west coast river basins. Despite apparent widespread distributions of both suitable fish hosts and the nominal annelid host, both parasites are restricted to river basins in the northwestern US and have never been recorded from the Great Lakes or the eastern US. In this study, we sampled 94 infected and uninfected annelids from two northwestern US rivers to confirm the identity of the host. We found these new specimens had mitochondrial COI sequences with no more than 4.5% distance from each other, but with at least 11% divergence from M. speciosa sampled from near the type locality (New Jersey) and Lake Superior. We did not recover any M. speciosa from either west coast river. The annelid from the Klamath and Willamette rivers showed marked sexual dimorphism that has not been reported in any Manayunkia described to date, though it is apparent that this had been missed in M. speciosa. Accordingly, we describe a new taxon, Manayunkia occidentalis sp. nov., and show that it can host both C. shasta and P. minibicornis. We suspect that previous records of Manayunkia from Pacific Northwest watersheds are likely to be M. occidentalis sp. nov. and not M. speciosa. Sampling of Manayunkia from additional localities is underway to test if the novel Manayunkia species is the only freshwater fabriciid annelid present across the Pacific Northwest.

&lt;p class="HeadingRunIn"&gt;&lt;strong&gt;The aquatic oligochaete fauna of Lake Çıldır, Ardahan-Kars, Turkey, including an updated checklist of freshwater annelids known to occur in the country&lt;/strong&gt;&lt;/p&gt;

In this paper, we present the results of the first survey for aquatic oligochaetes in Lake Çıldır, northeastern Turkey, during which 22 oligochaete species were recorded from the lake. The results of this survey were integrated into an updated and annotated list of oligochaetes and other aquatic annelids occurring in the country, summarized from historical and recent publications. Currently, the freshwater annelid fauna of Turkey includes 150 species of oligochaetes (1 Crassiclitellata, 21 Enchytraeidae, 1 Propappidae, 1 Haplotaxidae, 4 Lumbriculidae, 56 Naidinae, 64 Tubificinae, 2 Lumbricidae), 1 species of Branchiobdellida, and 6 species of Aphanoneura (1 Potamodrilidae and 5 Aeolosomatidae). Although studies focusing on the aquatic oligochaete fauna of Turkey have increased over the past 15–20 years, species diversity still remains unclear.

General characterization of regeneration in Aeolosoma viride (Annelida, Aeolosomatidae)

AbstractRegeneration has long been the focus of scientific interest for its potential to restore lost, damaged, or aged tissues and organs. A wide range of regenerative studies have been conducted on different vertebrate and invertebrate model organisms. Annelids are known for their regenerative capacities, and because of their relatively complex organ systems, they are an ideal organism for regeneration study. Our present work focused on the freshwater annelid Aeolosoma viride, an asexually reproducing annelid capable of regenerating both anteriorly and posteriorly. Even though regenerative ability has been documented in this animal in previous studies, detailed characterization of the process is still unavailable. The objective of this study was to evaluate the regenerative ability of A. viride. We described the sequential morphological events during the process of regeneration, such as wound healing and the formation of blastema, mouth, and pygidium. In order to clarify the capacity and type of regeneration, we conducted a series of observations and experiments using a cell proliferation assay. Massive proliferation and the absence of cell migration indicated that the animal regenerates primarily through epimorphosis. Our study of the epimorphic regenerative process of A. viride provides a clearer picture of the evolutionary origin of regeneration in annelids.

Telomere maintenance during anterior regeneration and aging in the freshwater annelid Aeolosoma viride

Aging is a complex process involving declines in various cellular and physical functionalities, including regenerative ability. Telomere maintenance is thought to be necessary for regeneration, and telomere attrition is one mechanism that contributes to aging. However, it is unclear if aging affects regeneration owing to deterioration of telomeric maintenance. We introduce Aeolosoma viride—a freshwater annelid with strong regenerative abilities—as a new model for studying the effects of aging on telomere functions and regeneration. We show that the anterior regenerative ability of A. viride declines with age. We characterized the A. viride telomere sequence as being composed of TTAGGG repeats and identifyied the telomerase gene Avi-tert. In adult A. viride, telomerase was constantly active and telomere lengths were similar among different body sections and stably maintained with age. Notably, we found that regeneration did not result in telomere shortening at regenerating sites. Moreover, transient up-regulation of Avi-tert expression and telomerase activity was observed at regenerating sites, which might promote telomere lengthening to counteract telomere erosion resulting from cell proliferation. Our study suggests that although aging affects A. viride regeneration independent of steady-state telomere length, timely regulation of telomerase functions is critical for the regeneration process in A. viride.

Impact of common environmental chemicals bisphenol A and bisphenol S on the physiology of Lumbriculus variegatus

Bisphenol A (BPA) is a component of polycarbonate plastics and a near ubiquitous environmental endocrine disrupting chemical. Bisphenol S (BPS), a substitute of BPA, is also hormonally active. This study examines the effects of aqueous exposure to BPA and BPS on the freshwater annelids Lumbriculus variegatus, a keystone species in shallow water ecosystems. Both BPA and BPS, at both low dose (10−9 M) and high dose (10-6 M), retarded the initial phase of body regrowth after cutting/fragmentation, which is the main mode of reproduction of L. variegatus. Both acute and five day exposure to BPA and BPS increased pulse rate of the dorsal blood vessel. For all the measured endpoints, the effects of BPA and BPS were nearly indistinguishable. These results indicate that BPA and BPS have similar and significant effects on the physiology of L. variegatus. These findings have implication for the potential impact of these bisphenols on invertebrates in the ecosystem.

Discordant population histories of host and its parasite: A role for ecological permeability of extreme environment?

Biogeographical and ecological barriers strongly affect the course of micro-evolutionary processes in free living organisms. Here we assess the impact of a recently emerged barrier on populations of limnic fauna. Genetic diversity and population structure in a host-parasite system (Wenyonia virilis tapeworm, Synodontis schall catfish) are analyzed in the recently divided Turkana and Nile basins. The two basins, were repeatedly connected during the Holocene wet/dry climatic oscillations, following late Pleistocene dessication of the Turkana basin. Mitochondrial DNA sequences for cytochrome oxidase I gene (cox I) and a whole genome scanning method—amplified fragment length polymorphism (AFLP) were employed. A total of 347 cox I sequences (representing 209 haplotypes) and 716 AFLP fragments, as well as 120 cox I sequences (20 haplotypes) and 532 AFLP fragments were obtained from parasites and hosts, respectively. Although results indicate that host and parasite populations share some formative traits (bottlenecks, Nilotic origin), their population histories/patterns differ markedly. Mitochondrial analysis revealed that parasite populations evolve significantly faster and show remarkably higher genetic variability. Analyses of both markers confirmed that the parasites undergo lineage fission, forming new clusters specific for either freshwater or saline parts of Lake Turkana. In congruence with the geological history, these clusters apparently indicate multiple colonisations of Lake Turkana from the Nile. In contrast, the host population pattern indicates fusion of different colonisation waves. Although fish host populations remain connected, saline habitats in Lake Turkana (absent in the Nile), apparently pose a barrier to the gene flow in the parasite, possibly due to its multihost lifecycle, which involves freshwater annelids. Despite partially corroborating mitochondrial results, AFLP data was not sufficiently informative for analyzing populations with recently mixed biogeographic histories.

Larval stages of Neoplagioporus elongatus (Goto and Ozaki, 1930) (Opecoelidae: Plagioporinae), with notes on potential second intermediate hosts

The morphology of sporocysts and cercariae of Neoplagioporus elongatus (Goto and Ozaki, 1930) is described for the first time. A cotylomicrocercous cercaria obtained from the sorbeoconch snail Semisulcospira nakasekoae was confirmed to be the cercaria of N. elongatus, based on the degree of sequence identity of the COI gene to that of adult worms. Freshwater annelids (oligochaetes and leeches) and some aquatic insects (odonates) were demonstrated experimentally to be potential second intermediate hosts.

Flow cytometry analysis of DNA ploidy levels and protein profiles distinguish between populations of Lumbriculus (Annelida: Clitellata)

AbstractVariations in DNA ploidy have been observed in Lumbriculus, a freshwater annelid, as well as in other clitellates. Interpretation and application of experimental results using these animals may be impacted as ploidy levels affect the protein expression, reproductive behavior, and response to stressors. Ploidy is typically determined by chromosome spreads, a time‐consuming and inefficient method. We adapted flow cytometry protocols used on vertebrates and plants to determine the ploidy levels in different populations of Lumbriculus, including a laboratory strain (Environmental Protection Agency), a commercial strain (Aquatic Foods), and worms collected from natural habitats. To isolate nuclei, worms were homogenized, filtered to remove cell debris, and centrifuged through Optiprep™ density gradients. Nuclei were recovered, treated with RNAse, and stained with propidium iodide. Flow cytometry of the labeled nuclei showed that Lumbriculus from natural habitats in Minnesota and Iowa were diploid, with an estimated genome size of 2.7 pg. Populations from natural habitats in California and Oregon were highly polyploid, as were the laboratory and commercial strains. Chromosome spreads verified the high ploidy levels indicated by flow cytometry results, but also suggested that flow cytometry may be underestimating the DNA content levels. Staining of nuclei with diamidino‐2‐phenylindole indicated that this may be due to high levels of heterochromatin in nuclei from polyploid forms of Lumbriculus. To further compare the populations, proteins in worm homogenates were subjected to isoelectrofocusing gel electrophoresis. Distinct protein profiles were seen; one was shared in common by the diploid worms, the other was characteristic of polyploid populations. Diploid worms could also be distinguished from polyploid worms based on differences in hemoglobin linker proteins. The results further support taxonomic classification of the diploid and polyploid forms of Lumbriculus as distinct species.

Faunistic survey on freshwater annelids from Korea

Faunistic survey on freshwater annelids from Korea

The Roles of Matrix Metalloproteinases in Anterior Regeneration in Aeolosoma viride

Matrix metalloproteinases (MMPs) play key roles in turnover of extracellular matrix (ECM) and serve as important regulators of cell‐ECM interaction during development and regeneration. In previous studies, MMP‐2, MMP‐9 and MMP‐14 are found involved in regenerative processes in vertebrates. However, in invertebrates, no MMP‐2 or MMP‐9 has been found. So, the function of MMPs in the regenerative ability of invertebrates is an interesting question. In this research, a fresh water annelid, Aeolosoma viride, with high regenerative ability, was used to solve out this question. In the NGS transcriptome data of A. viride, only four matrix metalloproteinases, named as AviMMP1, AviMMP2, AviMTMMP1 and AviMTMMP2, were found. GM6001, MMPs inhibitor, had been treated during regeneration in A. viride and found that inhibiting MMPs activities at the early stage of anterior regeneration could delay the whole regenerative process, which means MMPs play some roles at the early stage of regeneration. The sequences of MMPs had been cloned and, in phylogenetic tree, they grouped with MMPs of other species. The qPCR data of blastema at different regenerative time point showed that Avimmp2 and Avimtmmp2 expressed highly at the early stage of anterior regeneration, but Avimmp1 and Avimtmmp1 showed no differences in expression during anterior regeneration. In situ hybridization analysis also indicated that high expression of Avimmp2 in blastema at 12, 24 and 48 hours post amputation (hpa). These data suggested that the AviMMP2 might be involved in the early stage of regeneration. On the other hand, SDS‐PAGE gelatin zymography showed the highest protease activity at 24 hpa blastema. These data suggested that MMPs have some effects on early stage of anterior regeneration, and AviMTMMP2 and AviMMP2 might be the key factors in the processes. The relationship between MMPs and the regulation of MMPs need further research to resolve.

Cloning, Identification And Characterization of Two MyD88s during Anterior Regeneration in Aeolosoma viride

A 2 mm long freshwater annelid, belonging to Aeolosomatidae, with an exceptional regenerative ability, called Aeolosoma viride, serves as an excellent model for regenerative research. Additional reasons are its small size and semi‐transparent color, which allow manageable culture and experimentation. A. viride can regenerate its amputated head with a functional brain within 5 days. The regeneration process includes several steps, starting with wound repair followed by blastema formation and tissue remodeling. In addition, the immune system and inflammatory responses associated with injury to prevent deadly infections have been implicated as critical modulators during wound healing and regeneration. The aim of our study is to unravel the involvement of immune responses in A. viride regeneration. The Toll‐like receptor (TLR) signaling pathway is one of many pathogen recognition mechanisms, which initiates by ligand binding to the receptors and then recruits myeloid differentiation factor 88 (MyD88) to serve as an adaptor molecule to activate the transcription factor NF‐κB. Two MyD88 sequences have been cloned from A. viride. Based on blasting results, one of the sequences has two regular functional domains of MyD88, namely Toll/IL‐1R (TIR) domain and death domain. However, the other one lacks the TIR domain, responsible for TLR binding. Furthermore, we identified and analyzed their gene expressions during the regenerative process. Real‐time PCR results of blastemal tissue showed different expression patterns of these two genes. One is down‐regulated during blastema formation, while the other is up‐regulated during wound healing. Therefore, we propose the two MyD88s may play different roles during regeneration in A. viride. Avi‐MyD88a and Avi‐MyD88i may activate or inactive the TLR pathway.