A comprehensive review:Research status and trends of planarianology in China

Planarian is an excellent model for studying several scientific issues,and planarianology has become an active research field in the world.Researchers at home and abroad have conducted a lot of in-depth studies on planarians in various areas.This paper outlined the panorama of planarian research in China and summarized the advances from three aspects of taxonomy,molecular phylogeny and phylogeography,regeneration,tissue homeostasis and immunity as well as toxicology.Furthermore,the current problems and future development direction and tendency of planarian research in China are briefly analyzed and prospected.Importantly,the catalogue of planarians in China is also presented.

Systematic identification and screening of functional long noncoding RNAs during planarian regeneration

Freshwater planarians(Platyhelminthes)are ideal models in regenerative biology because of their whole-body regeneration capability(Salo,2006).They are also popular in neuroscience because they possess anterior cephalic ganglia(brains),which can be restored within a week after head removal(Ross et al.,2017).

Photokinesis and Djopsin gene expression analysis during the regeneration of planarian eyes

Planarians provide the ideal model for studying eye development,with their simple eye structure and exceptionally rapid regeneration.Here,we observed the eye morphogenesis,photophobic behavior,spectral sensitivity and expression pattern of Djopsin in the freshwater planarian Dugesia japonica.The results showed that:(i)Djopsin encoding the putative protein belonged to the rhabdomeric opsins group and displayed high conservation during animal evolution;(ii)planarians displayed diverse photophobic response to different visible wavelengths and were more sensitive to light blue(495 nm)and yellow(635 nm);(iii)the morphogenesis and functional recovery of eyes were related to the expression pattern of Djopsin during head regeneration;and(iv)Djopsin gene plays a major role in functional recovery during eye regeneration and visual system maintenance in adult planarians.

Genetic diversity,population structure and demographic history of Dugesia japonica in Taihang Mountains

The freshwater planarian Dugesia japonica has become a model organism in regeneration biology and toxicology due to its powerful regeneration capability and highly chemical sensitivity.Nonetheless,little is known about its evolutionary history and demographics.Taihang Mountains is the natural boundary between the Loess Plateau and the North China Plain,and is considered as one of the important priority areas for biodiversity conservation in China.In order to figure out the genetic diversity,population structure and demographic history of D.japonica in Taihang Mountains,a study based on the mitochondrial COI from 116 individuals sampled across 20 populations has been conducted.The results showed that the 116 COI sequences yielded 32 haplotypes,including 8 shared haplotypes and 24 private ones.The overall haplotype diversity(Hd)and nucleotide diversity(π)were 0.920 and 0.083,respectively.Even though the AMOVA results suggested that the genetic variation among populations was significant(FST=0.480,P<0.01),the phylogeny and haplotype network analysis based on 32 haplotypes revealed no obvious phylogeographic pattern.Furthermore,the significantly positive values of neutrality test(Tajima’s D=2.596,P<0.05;Fu’s Fs=2.769,P<0.01)together with the multimodal arrangement of mismatch distribution indicated that D.japonica in Taihang Mountains would have been undergoing population decline.We hope these findings will arouse conservation and management strategy regarding freshwater planarians and contribute to the biodiversity in the long run.

Integrative taxonomy unveils a new species of Dugesia(Platyhelminthes,Tricladida,Dugesiidae)from the southern portion of the Taihang Mountains in northern China,with the description of its complete mitogenome and an exploratory analysis of mitochondrial gene order as a taxonomic character

A new species of Dugesia(Platyhelminthes,Tricladida,Dugesiidae)from northern China is described on the basis of an integrative approach,involving morphology,karyology,histology,molecular distance,molecular phylogeny,and mitochondrial gene order.Here,we present the complete mitogenome of the new species Du-gesia constrictiva Chen&Dong,sp.nov.This new species is mainly characterized by the presence of the following features:asymmetrical openings of the oviducts;large,cuboidal copulatory bursa;vasa deferentia opening through the ventro-lateral wall of the seminal vesicle;laterally compressed seminal vesicle;ventrally displaced ejaculatory duct,opening at the blunt tip of the penis papilla;long duct intercalated between semi-nal vesicle and diaphragm;chromosome complement diploid,with 16 metacentric chromosomes;mitochondrial gene order as follows:cox1-E-nad6-nad5-S2-D-R-cox3-I-Q-K-atp6-V-nad1-W-cox2-P-nad3-A-nad2-M-H-F-rrnS-L1-Y-G-S1-rrnL-L2-T-atp8-C-N-cob-nad4l-nad4.In triclads,mitochondrial gene order is considerably conserved between freshwater planarians and landflatworms,whereas it is variable between marine planarians and both fresh-water and landflatworms.The secondary structures of tRNAs are all equipped with 4 arms,excepting tRNA S1 and tRNA S2,which lack the D arm and have excessively enlarged loops.Numerous transpositions of tRNA are present between D.constrictiva and its congeners.Mitochondrial gene arrangements may form a new,additional tool for taxonomic studies.The phylogenetic tree based on analysis of the mitochondrial genome basically corroborates current classification of the higher taxa of planarianflatworms.