Transcriptome Responses to Different Environments in Intertidal Zones in the Peanut Worm Sipunculus nudus.

The peanut worm (Sipunculus nudus) is an important intertidal species worldwide. Species living in the same aquaculture area might suffer different environmental impacts. To increase knowledge of the molecular mechanisms underlying the response to environmental fluctuations, we performed a transcriptome analysis of S. nudus from different intertidal zones using a combination of the SMRT platform and the Illumina sequencing platform. (1) A total of 105,259 unigenes were assembled, and 23,063 unigenes were perfectly annotated. The results of the PacBio Iso-Seq and IIIumina RNA-Seq enriched the genetic database of S. nudus. (2) A total of 830 DEGs were detected in S. nudus from the different groups. In particular, 33 DEGs had differential expression in the top nine KEGG pathways related to pathogens, protein synthesis, and cellular immune response and signaling. The results indicate that S. nudus from different zones experience different environmental stresses. (3) Several DEGs (HSPA1, NFKBIA, eEF1A, etc.) in pathways related to pathogens (influenza A, legionellosis, measles, and toxoplasmosis) had higher expression in groups M and L. HSPA1 was clearly enriched in most of the pathways, followed by NFKBIA. The results show that the peanut worms from the M and L tidal flats might have suffered more severe environmental conditions. (4) Some DEGs (MKP, MRAS, and HSPB1) were upregulated in peanut worms from the H tidal flat, and these DEGs were mainly involved in the MAPK signaling pathway. These results indicate that the MAPK pathway may play a vital role in the immune response of the peanut worm to the effects of different intertidal flats. This study provides a valuable starting point for further studies to elucidate the molecular basis of the response to different environmental stresses in S. nudus.

Complete mitochondrial genome of Toxabramis houdemeri (Cypriniformes; Cyprinidae) and its phylogenetic analysis.

Toxabramis houdemeri belongs to the genus Toxabramis in the subfamily of Cultrinae (Cyprinidae). We first determine the complete mitochondrial genome of T. houdemeri in this study. It is 16 618 bp in length, with the base composition on the heavy strand: 30.79% A, 16.61% G, 27.29% C, and 25.31% T. It has the typical vertebrate mitochondrial gene arrangement, including 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes, and a D-loop region. Phylogenetic analysis showed that T. houdemeri was clustered into one branch of the subfamily of Cultrinae, and closely related to Hemiculter leucisculus. The present study will contribute to genetic resources conservation of T. houdemeri and studying its population genetic structure and phylogenetic relationships.

The complete mitochondrial genome of Arius arius (Siluriformes: Ariidae).

The threadfin sea catfish (Arius arius) belongs to the genus Arius in Ariidae. In this paper, we initially determined the complete mitochondrial genome of Arius arius. The mitochondrial genome is 16, 711 bp in length, with the base composition on the heavy strand: A - 29.67%, T - 25.38%, C - 29.70% and G - 15.25%. It has the typical vertebrate mitochondrial gene arrangement, including 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes and a control region. Phylogenetic analysis showed that A. arius was clustered into the order of Siluriformes, and closely related to species in the family of Siluridae. The present study would contribute to genetic resources conservation and systematics study of A. arius.

The complete mitochondrial genome of Onychostoma barbatum of Youjiang River.

Onychostoma barbatum is an endemic species to China. In the present study, the complete mitochondrial genome of O. barbatum in Youjiang River was cloned and analyzed. The complete mitochondrial genome is 16 589 bp in length, with the base composition: A - 31.5%, T - 24.5%, C - 28.1%, and G - 15.9%. It had the typical vertebrate mitochondrial gene arrangement, including 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes and a D-loop region. The diversity of sequences and the phylogenetic tree approve that it has high similarity with that in Guijiang River. The mitochondrial genome would contribute to protection of the germplasm resources of O. barbatum and studying its population structure and dynamics in the future.

Transcriptional variants of Dmrt1 and expression of four Dmrt genes in the blunt snout bream, Megalobrama amblycephala.

Doublesex and Mab3 related transcription factor (DMRT), characterized by a conserved DM domain, function as sex-related transcription factors and also play critical roles in ontogenesis. In this study, 4 Dmrt genes in the blunt snout bream, Megalobrama amblycephala, were identified, characterized and their mRNA expression in different adult organs, during embryogenesis and gonadal development in larvae were determined by quantitative real time PCR. There are 4 Dmrt1 isoforms in the M. amblycephala genome, which were expressed highly in the testis and weakly in the ovary. The complete cDNAs of the M. amblycephala Dmrt2a, Dmrt2b and Dmrt3 were predicted to encode 510, 328 and 449 amino acids, respectively. The M. amblycephala Dmrt2a mRNA peaked at 11hpf (hour post fertilizing) during early embryonic stages, while Dmrt2b was highly expressed during late embryonic stages. Both the M. amblycephala Dmrt2a and Dmrt2b were expressed highly in the gill and exhibited a sexually dimorphic expression pattern. The M. amblycephala Dmrt3 was expressed highly in the gill, muscle and brain, at 40dph (day post hatching) during early development and at stage V in the testis during gonadal development. All fish Dmrts except Dmrt5 were found in the M. amblycephala genome. The observed expression patterns of these Dmrts in developing embryos and larvae, as well as different adult organs indicate conserved sexual or extragonadal functions of the Dmrts through evolution.

Molecular cloning and expression analysis of major histocompatibility complex class I, IIA and IIB genes of blunt snout bream (Megalobrama amblycephala).

Major histocompatibility complex (MHC) plays an important role in the immune response of vertebrates. In this study, we isolated MHC class IIA and IIB genes from blunt snout bream (Megalobrama amblycephala) by rapid amplification of cDNA ends polymerase chain reaction (RACE-PCR). In order to study the function of the MHC genes in M. amblycephala, tissue distribution and immune response of the MHC genes to bacterial challenge were analyzed. All the characteristic features of MHC class II chain structure could be identified in the deduced amino sequences of MHC IIA and IIB, including the leader peptide, α1/ß1 and α2/ß2 domains, connecting peptide and transmembrane and cytoplasmic regions, as well as conserved cysteines and N-glycosylation site. The deduced amino acid sequence of the MHC IIA and IIB molecules shared from 48% to 88% and from 65% to 77% similarity with those of other teleosts, respectively. Quantitative real-time PCR (qRT-PCR) demonstrated that MHC I and II genes were ubiquitously expressed in ten tissues, with high level in immune related tissues, including kidney, intestine, gill and spleen. Challenge of M. amblycephala with the extracellular pathogen, Aeromonas hydrophila, resulted in a significant increase in the expression of MHC I, MHC IIA and IIB mRNA within 72 h after infection in gill, kidney, intestine and liver, followed by a recovery to normal level after 120 h. The changes of expression levels for MHC IIA and IIB in most tissues were significantly higher than that of MHC I in the corresponding tissues at most time points (P<0.05). These results demonstrated the MHC genes played an important role in response to bacterial infection in M. amblycephala; however, MHC class I and II genes showed different functional activity, which need be further investigated in teleost.