Djrho2 is involved in regeneration of visual nerves in Dugesia japonica

DjFARP Contributes to the Regeneration and Maintenance of the Brain through Activation of DjRac1 in Dugesia japonica

FERM, RhoGEF, and Pleckstrin domain protein (FARP) mediated RhoGTPase pathways are involved in diverse biological processes, such as neuronal development and tumorigenesis. However, little is known about their role in neural regeneration. We uncovered for the first time that FARP-Rac1 signaling plays an important role in neural regeneration in Dugesia japonica, a planarian that possesses unparalleled regenerative capacities. The planarian FARP homolog DjFARP was primarily expressed in both intact and regenerating brain and pharynx tissue. Functional studies suggested that downregulation of DjFARP with dsRNA in Dugesia japonica led to smaller brain sizes, defects in brain lateral branches, and loss of cholinergic, GABAergic, and dopaminergic neurons in both intact and regenerating animals. Moreover, the Rho GTPase DjRac1 was shown to play a similar role in neural regeneration and maintenance. Rac1 activation assay showed that DjFARP acts as a guanine nucleotide exchange factor (GEF) for DjRac1. Together, these findings indicate that the brain defects seen in DjFARP knockdown animals may be attributable to DjRac1 inactivation. In conclusion, our study demonstrated that DjFARP-DjRac1 signaling was required for the maintenance and proper regeneration of the brain in Dugesia japonica.

Proteomics and systems biology in optic nerve regeneration

We present an overview of current state of proteomic approaches as applied to optic nerve regeneration in the historical context of nerve regeneration particularly central nervous system neuronal regeneration. We present outlook pertaining to the optic nerve regeneration proteomics that the latter can extrapolate information from multi-systems level investigations. We present an account of the current need of systems level standardization for comparison of proteome from various models and across different pharmacological or biophysical treatments that promote adult neuron regeneration. We briefly overview the need for deriving knowledge from proteomics and integrating with other omics to obtain greater biological insight into process of adult neuron regeneration in the optic nerve and its potential applicability to other central nervous system neuron regeneration.

A novel RhoA-related gene, DjRhoA, contributes to the regeneration of brain and intestine in planarian Dugesia japonica

A small GTPase, RhoA, plays a variety of functions in the regulation of cellular and developmental events via its downstream effectors, including cytokinesis, cell migration, and phagocytosis. In this study, a novel RhoA-related gene from the planarian Dugesia japonica, DjRhoA, was cloned and characterized. The full-length cDNA of DjRhoA is 869 bp, and the open reading frame encodes a poly-peptide of 194 amino acids. Phylogenetic analysis revealed that DjRhoA clustered with another RhoA-related protein, DjRho2, and located on the base of phylogenetic tree. Whole-mount in situ hybridization results indicated that DjRhoA was expressed in the brain primordia and intestine during regeneration. Knockdown of DjRhoA induces defects in the brain and intestine. These results suggested that DjRhoA was responsible for the regeneration of brain and intestine in Dugesia japonica.

Unusually Large Number of Mutations in Asexually Reproducing Clonal Planarian Dugesia japonica

We established a laboratory clonal strain of freshwater planarian (Dugesia japonica) that was derived from a single individual and that continued to undergo autotomous asexual reproduction for more than 20 years, and we performed large-scale genome sequencing and transcriptome analysis on it. Despite the fact that a completely clonal strain of the planarian was used, an unusually large number of mutations were detected. To enable quantitative genetic analysis of such a unique organism, we developed a new model called the Reference Gene Model, and used it to conduct large-scale transcriptome analysis. The results revealed large numbers of mutations not only outside but also inside gene-coding regions. Non-synonymous SNPs were detected in 74% of the genes for which valid ORFs were predicted. Interestingly, the high-mutation genes, such as metabolism- and defense-related genes, were correlated with genes that were previously identified as diverse genes among different planarian species. Although a large number of amino acid substitutions were apparently accumulated during asexual reproduction over this long period of time, the planarian maintained normal body-shape, behaviors, and physiological functions. The results of the present study reveal a unique aspect of asexual reproduction.

Inhibition of planar cell polarity extends neural growth during regeneration, homeostasis, and development

The ability to stop producing or replacing cells at the appropriate time is essential, as uncontrolled growth can lead to loss of function and even cancer. Tightly regulated mechanisms coordinate the growth of stem cell progeny with the patterning needs of the host organism. Despite the importance of proper termination during regeneration, cell turnover, and embryonic development, very little is known about how tissues determine when patterning is complete during these processes. Using planarian flatworms, we show that the planar cell polarity (PCP) pathway is required to stop the growth of neural tissue. Although traditionally studied as regulators of tissue polarity, we found that loss of the PCP genes Vangl2, DAAM1, and ROCK by RNA interference (individually or together) resulted in supernumerary eyes and excess optical neurons in intact planarians, while regenerating planarians had continued hyperplasia throughout the nervous system long after controls ceased new growth. This failure to terminate growth suggests that neural tissues use PCP as a readout of patterning, highlighting a potential role for intact PCP as a signal to stem and progenitor cells to halt neuronal growth when patterning is finished. Moreover, we found this mechanism to be conserved in vertebrates. Loss of Vangl2 during normal development, as well as during Xenopus tadpole tail regeneration, also leads to the production of excess neural tissue. This evolutionarily conserved function of PCP represents a tractable new approach for controlling the growth of nerves.