cGAS suppresses ß-cell proliferation by a STING-independent but CEBPß-dependent mechanism.

AIMS/HYPOTHESIS: cGAS (cyclic GMP-AMP synthase) has been implicated in various cellular processes, but its role in ß-cell proliferation and diabetes is not fully understood. This study investigates the impact of cGAS on ß-cell proliferation, particularly in the context of diabetes. METHODS: Utilizing mouse models, including cGAS and STING (stimulator of interferon genes) knockout mice, we explored the role of cGAS in ß-cell function. This involved ß-cell-specific cGAS knockout (cGASßKO) mice, created by breeding cGAS floxed mice with transgenic mice expressing Cre recombinase under the insulin II promoter. We analyzed cGAS expression in diabetic mouse models, evaluated the effects of cGAS deficiency on glucose tolerance, and investigated the molecular mechanisms underlying these effects through RNA sequencing. RESULTS: cGAS expression is upregulated in the islets of diabetic mice and by high glucose treatment in MIN6 cells. Both global cGAS deficiency and ß-cell-specific cGAS knockout mice lead to improved glucose tolerance by promoting ß-cell mass. Interestingly, STING knockout did not affect pancreatic ß-cell mass, suggesting a STING-independent mechanism for cGAS's role in ß-cells. Further analyses revealed that cGAS- but not STING-deficiency leads to reduced expression of CEBPß, a known suppressor of ß-cell proliferation, concurrently with increased ß-cell proliferation. Moreover, overexpression of CEBPß reverses the upregulation of Cyclin D1 and D2 induced by cGAS deficiency, thereby regulating ß-cell proliferation. These results confirm that cGAS regulation of ß-cell proliferation via a CEBPß-dependent but STING-independent mechanism. CONCLUSIONS/INTERPRETATION: Our findings highlight the pivotal role of cGAS in promoting ß-cell proliferation and maintaining glucose homeostasis, potentially by regulating CEBPß expression in a STING-independent manner. This study uncovers the significance of cGAS in controlling ß-cell mass and identifies a potential therapeutic target for enhancing ß-cell proliferation in the treatment of diabetes.

Serum acylcarnitines levels as a potential predictor for gestational diabetes: a systematic review and meta-analysis.

Aims: Gestational diabetes mellitus (GDM) stands as a prevalent obstetric complication bearing consequential health implications for both mother and child. While existing studies have probed the alterations in acylcarnitines during GDM, an updated systematic meta-analysis is needed to consolidate these findings. Hence, this study endeavours to furnish a comprehensive systematic review and meta-analysis delineating the association between acylcarnitines and GDM, aimed at bolstering diagnostic accuracy and preventive measures against GDM. Methods: To extract pertinent studies for this meta-analysis, we meticulously scoured databases such as PubMed, Web of Science, Embase, and Cochrane Library up until May 2023. The inclusion criteria were studies contrasting plasma metabolomics between two cohorts: women diagnosed with GDM and normoglycemic pregnant women. Weighted mean differences (SMDs) and 95% confidence intervals (CIs) were calculated using random-effects models. The I2 index was employed to quantify heterogeneity amongst the studies. All meta-analyses were executed using Stata version 12.0. Results: Our meta-analysis included eight studies encompassing 878 pregnant women. The analysis disclosed that relative to normoglycemic pregnant women, women with GDM exhibited significantly elevated levels of Short-Chain Acylcarnitines (SCAC) (SMD: 0.19, 95% CI: 0.02-0.36, I2 = 71.3%). No substantial difference was discerned in fasting total carnitine levels (SMD: 0.15, 95% CI: -0.16-0.31, I2 = 68.2%), medium-chain acylcarnitines (MCAC) (SMD: 0.08, 95% CI: -0.02-0.36, I2 = 79.0%), and long-chain acylcarnitines (LCAC) (SMD: 0.04, 95% CI: -0.06-0.15, I2 = 0%). Neither funnel plot assessment nor Egger's regression and Begg's rank correlation tests indicated any evidence of publication bias. Conclusion: Our meta-analysis suggests that elevated levels of SCAC may heighten the risk of GDM onset. Given GDM's deleterious impact on pregnant women and their offspring, these findings underscore the clinical imperative of managing this condition. Early surveillance of plasma metabolomic profiles, particularly serum acylcarnitine concentrations, may equip clinicians with a valuable tool for timely diagnosis and intervention in GDM.

Hypothalamic Grb10 enhances leptin signalling and promotes weight loss.

Leptin acts on hypothalamic neurons expressing agouti-related protein (AgRP) or pro-opiomelanocortin (POMC) to suppress appetite and increase energy expenditure, but the intracellular mechanisms that modulate central leptin signalling are not fully understood. Here we show that growth factor receptor-bound protein 10 (Grb10), an adaptor protein that binds to the insulin receptor and negatively regulates its signalling pathway, can interact with the leptin receptor and enhance leptin signalling. Ablation of Grb10 in AgRP neurons promotes weight gain, while overexpression of Grb10 in AgRP neurons reduces body weight in male and female mice. In parallel, deletion or overexpression of Grb10 in POMC neurons exacerbates or attenuates diet-induced obesity, respectively. Consistent with its role in leptin signalling, Grb10 in AgRP and POMC neurons enhances the anorexic and weight-reducing actions of leptin. Grb10 also exaggerates the inhibitory effects of leptin on AgRP neurons via ATP-sensitive potassium channel-mediated currents while facilitating the excitatory drive of leptin on POMC neurons through transient receptor potential channels. Our study identifies Grb10 as a potent leptin sensitizer that contributes to the maintenance of energy homeostasis by enhancing the response of AgRP and POMC neurons to leptin.

Re-evaluation of the taxonomic status of four nominal, western Pacific species of tongue soles (Pleuronectoidei: Cynoglossidae: Cynoglossus), with redescription of C. joyneri Gnther, 1878.

Striking similarities in morphological characters and significant overlap in meristic features have resulted in different hypotheses regarding the taxonomic status of several nominal species of northwestern Pacific tongue soles of the genus Cynoglossus, including C. joyneri Gnther, 1878, C. lighti Norman, 1925, C. tenuis (Oshima, 1927), and C. tshusanensis Chabanaud, 1951. Previous hypotheses have proposed that each taxon is a valid species; or that C. lighti and C. tshusanensis are junior subjective synonyms of C. joyneri; or that C. tenuis is a junior subjective synonym of either C. joyneri or C. lighti. Although several previous investigations concluded that C. lighti is a synonym of C. joyneri, names of both nominal species still appear in contemporary literature indicating that taxonomic status of these nominal species remains unresolved. To clarify the taxonomic status of these four nominal species, detailed study of morphological characters of 138 specimens collected from 22 localities in Japan and China, and re-examination of type specimens of three of these nominal species was conducted. The molecular barcodes of mitochondrial DNA from six representative specimens featuring morphological variation purportedly useful for distinguishing C. lighti from C. joyneri were also analyzed and then compared with sequences reported for C. joyneri in the literature. Lectotypes of C. joyneri and C. lighti differed in only two morphological characters (body depth and position of posterior tip of rostral hook relative to anterior margin of lower eye). However, when these two characters were examined in 138 recently collected non-type specimens, no differences were found among these nominal species. Our results do not support recognizing these as separate species. Results from genetic analyses also support recognizing only a single species among the material examined. Furthermore, overall similarities in morphological features between the holotype of C. tshusanensis and specimens of C. joyneri support recognizing C. tshusanensis as a junior subjective synonym of C. joyneri. Likewise, values for morphological features of C. joyneri examined in the present study also encompass the range of values reported in the original description of C. tenuis. This finding supports conclusions of previous studies that this nominal species is also a junior synonym of C. joyneri. Based on morphological and genetic evidence, we conclude that only a single species, C. joyneri, should be recognized among the four nominal species included in this study. Cynoglossus joyneri is re-described based on data from 492 specimens collected throughout nearly the entire range of the species.

The adipocyte-enriched secretory protein tetranectin exacerbates type 2 diabetes by inhibiting insulin secretion from ß cells.

Pancreatic ß cell failure is a hallmark of diabetes. However, the causes of ß cell failure remain incomplete. Here, we report the identification of tetranectin (TN), an adipose tissue-enriched secretory molecule, as a negative regulator of insulin secretion in ß cells in diabetes. TN expression is stimulated by high glucose in adipocytes via the p38 MAPK/TXNIP/thioredoxin/OCT4 signaling pathway, and elevated serum TN levels are associated with diabetes. TN treatment greatly exacerbates hyperglycemia in mice and suppresses glucose-stimulated insulin secretion in islets. Conversely, knockout of TN or neutralization of TN function notably improves insulin secretion and glucose tolerance in high-fat diet-fed mice. Mechanistically, TN binds with high selectivity to ß cells and inhibits insulin secretion by blocking L-type Ca2+ channels. Our study uncovers an adipocyte-ß cell cross-talk that contributes to ß cell dysfunction in diabetes and suggests that neutralization of TN levels may provide a new treatment strategy for type 2 diabetes.

Synthesis and Bioactivities of Novel Galactoside Derivatives Containing 1,3,4-Thiadiazole Moiety.

A series of novel galactoside derivatives containing 1,3,4-thiadiazole moiety were synthesized, and the structure of them was verified by spectroscopy of NMR and HRMS, and antifungal and antibacterial activities of them were screened. The results showed that the newly synthesized compounds had good antifungal activities. Among them, Ⅲ16, Ⅲ17, and Ⅲ19 exhibited satisfactory activities against Phytophthora infestans (P. infestans), with EC50 values of 5.87, 4.98, and 6.17 µg/ml, respectively, which were similar to those of dimethomorph (5.52 µg/ml). Meanwhile, the title compounds also possessed certain antibacterial activities.

GRB10 regulates ß-cell mass by inhibiting ß-cell proliferation and stimulating ß-cell dedifferentiation.

Decreased functional ß-cell mass is the hallmark of diabetes, but the cause of this metabolic defect remains elusive. Here, we show that the levels of the growth factor receptor-bound protein 10 (GRB10), a negative regulator of insulin and mTORC1 signaling, are markedly induced in islets of diabetic mice and high glucose-treated insulinoma cell line INS-1 cells. ß-cell-specific knockout of Grb10 in mice increased ß-cell mass and improved ß-cell function. Grb10-deficient ß-cells exhibit enhanced mTORC1 signaling and reduced ß-cell dedifferentiation, which could be blocked by rapamycin. On the contrary, Grb10 overexpression induced ß-cell dedifferentiation in MIN6 cells. Our study identifies GRB10 as a critical regulator of ß-cell dedifferentiation and ß-cell mass, which exerts its effect by inhibiting mTORC1 signaling.

LRG1 is an adipokine that mediates obesity-induced hepatosteatosis and insulin resistance.

Dysregulation in adipokine biosynthesis and function contributes to obesity-induced metabolic diseases. However, the identities and functions of many of the obesity-induced secretory molecules remain unknown. Here, we report the identification of leucine-rich alpha-2-glycoprotein 1 (LRG1) as an obesity-associated adipokine that exacerbates high fat diet-induced hepatosteatosis and insulin resistance. Serum levels of LRG1 were markedly elevated in obese humans and mice compared with their respective controls. LRG1 deficiency in mice greatly alleviated diet-induced hepatosteatosis, obesity, and insulin resistance. Mechanistically, LRG1 bound with high selectivity to the liver and promoted hepatosteatosis by increasing de novo lipogenesis and suppressing fatty acid ß-oxidation. LRG1 also inhibited hepatic insulin signaling by downregulating insulin receptor substrates 1 and 2. Our study identified LRG1 as a key molecule that mediates the crosstalk between adipocytes and hepatocytes in diet-induced hepatosteatosis and insulin resistance. Suppressing LRG1 expression and function may be a promising strategy for the treatment of obesity-related metabolic diseases.

Rheb1 promotes glucose-stimulated insulin secretion in human and mouse ß-cells by upregulating GLUT expression.

Reduced ß-cell mass and impaired ß-cell function are primary causes of all types of diabetes. However, the intrinsic molecular mechanism that regulates ß-cell growth and function remains elusive. Here, we demonstrate that the small GTPase Rheb1 is a critical regulator of glucose-stimulated insulin secretion (GSIS) in ß-cells. Rheb1 was highly expressed in mouse and human islets. In addition, ß-cell-specific knockout of Rheb1 reduced the ß-cell size and mass by suppressing ß-cell proliferation and increasing ß-cell apoptosis. However, tamoxifen-induced deletion of Rheb1 in ß-cells had no significant effect on ß-cell mass and size but significantly impaired GSIS. Rheb1 facilitates GSIS in human or mouse islets by upregulating GLUT1 or GLUT2 expression, respectively, in a mTORC1 signaling pathway-dependent manner. Our findings reveal a critical role of Rheb1 in regulating GSIS in ß-cells and identified a new target for the therapeutic treatment of diabetes mellitus.

The miR-182-5p/FGF21/acetylcholine axis mediates the crosstalk between adipocytes and macrophages to promote beige fat thermogenesis.

A dynamically regulated microenvironment, which is mediated by crosstalk between adipocytes and neighboring cells, is critical for adipose tissue homeostasis and function. However, information on key molecules and/or signaling pathways regulating the crosstalk remains limited. In this study, we identify adipocyte miRNA-182-5p (miR-182-5p) as a crucial antiobesity molecule that stimulated beige fat thermogenesis by promoting the crosstalk between adipocytes and macrophages. miR-182-5p was highly enriched in thermogenic adipocytes, and its expression was markedly stimulated by cold exposure in mice. In contrast, miR-182-5p expression was significantly reduced in adipose tissues of obese humans and mice. Knockout of miR-185-5p decreased cold-induced beige fat thermogenesis whereas overexpression of miR-185-5p increased beiging and thermogenesis in mice. Mechanistically, miR-182-5p promoted FGF21 expression and secretion in adipocytes by suppressing nuclear receptor subfamily 1 group D member 1 (Nr1d1) at 5'-UTR, which in turn stimulates acetylcholine synthesis and release in macrophages. Increased acetylcholine expression activated the nicotine acetylcholine receptor in adipocytes, which stimulated PKA signaling and consequent thermogenic gene expression. Our study reveals a key role of the miR-182-5p/FGF21/acetylcholine/acetylcholine receptor axis that mediates the crosstalk between adipocytes and macrophages to promote beige fat thermogenesis. Activation of the miR-182-5p-induced signaling pathway in adipose tissue may be an effective approach to ameliorate obesity and associated metabolic diseases.

Synthesis and Bioactivities of Novel 1,3,4-Thiadiazole Derivatives of Glucosides.

A series of novel 1,3,4-thiadiazole derivatives of glucosides were synthesized by the starting materials d-glucose and 5-amino-1,3,4-thiadiazole-2-thiol in good yields with employing a convergent synthetic route. The results of bioactivities showed that some of the target compounds exhibited good antifungal activities. Especially, compounds 4i showed higher bioactivities against Phytophthora infestans (P. infestans), with the EC50 values of 3.43, than that of Dimethomorph (5.52 µg/ml). In addition, the target compounds exhibited moderate to poor antibacterial activities against Xanthomonas oryzae pv. oryzae (Xoo), Xanthomonas campestris pv. citri (Xcc).

Large-scale sequencing of flatfish genomes provides insights into the polyphyletic origin of their specialized body plan.

The evolutionary and genetic origins of the specialized body plan of flatfish are largely unclear. We analyzed the genomes of 11 flatfish species representing 9 of the 14 Pleuronectiforme families and conclude that Pleuronectoidei and Psettodoidei do not form a monophyletic group, suggesting independent origins from different percoid ancestors. Genomic and transcriptomic data indicate that genes related to WNT and retinoic acid pathways, hampered musculature and reduced lipids might have functioned in the evolution of the specialized body plan of Pleuronectoidei. Evolution of Psettodoidei involved similar but not identical genes. Our work provides valuable resources and insights for understanding the genetic origins of the unusual body plan of flatfishes.

DsbA-L deficiency in T cells promotes diet-induced thermogenesis through suppressing IFN-γ production.

Adipose tissue-resident T cells have been recognized as a critical regulator of thermogenesis and energy expenditure, yet the underlying mechanisms remain unclear. Here, we show that high-fat diet (HFD) feeding greatly suppresses the expression of disulfide-bond A oxidoreductase-like protein (DsbA-L), a mitochondria-localized chaperone protein, in adipose-resident T cells, which correlates with reduced T cell mitochondrial function. T cell-specific knockout of DsbA-L enhances diet-induced thermogenesis in brown adipose tissue (BAT) and protects mice from HFD-induced obesity, hepatosteatosis, and insulin resistance. Mechanistically, DsbA-L deficiency in T cells reduces IFN-γ production and activates protein kinase A by reducing phosphodiesterase-4D expression, leading to increased BAT thermogenesis. Taken together, our study uncovers a mechanism by which T cells communicate with brown adipocytes to regulate BAT thermogenesis and whole-body energy homeostasis. Our findings highlight a therapeutic potential of targeting T cells for the treatment of over nutrition-induced obesity and its associated metabolic diseases.

Reduced Compensatory ß-Cell Proliferation in Nfatc3-Deficient Mice Fed on High-Fat Diet.

BACKGROUND: High-fat-diet induces pancreatic ß-cell compensatory proliferation, and impairments in pancreatic ß-cell proliferation and function can lead to defects in insulin secretion and diabetes. NFATc3 is important for HFD-induced adipose tissue inflammation. But it is unknown whether NFATc3 is required for ß cell compensatory growth in mice fed with HFD. METHODS: NFATc3 mRNA and protein expression levels were quantified by RT-qPCR and Western blotting, respectively, in pancreatic islets of WT mice fed on HFD for 12-20 weeks. Adenoviral-mediated overexpression of NFATc3 were conducted in Min6 cells and cultured primary mouse islets. NFATc3-/- mice and WT control mice were fed with HFD and metabolic and functional parameters were measured. RESULTS: We observed that the NFATc3 expression level was reduced in the islets of high-fat-diet (HFD)-fed mice. Adenovirus-mediated overexpression of NFATc3 enhanced glucose-stimulated insulin secretion and ß-cell gene expression in cultured primary mouse islets. Nfatc3-/- mice initially developed similar glucose tolerance at 2-4 weeks after HFD feeding than HFD-fed WT mice, but Nfatc3-/- mice developed improved glucose tolerance and insulin sensitivity after 8 weeks of HFD feeding compared to Nfatc3+/+fed with HFD. Furthermore, Nfatc3-/- mice on HFD exhibited decreased ß-cell mass and reduced expression of genes important for ß-cell proliferation and function compared to Nfatc3+/+mice on HFD. CONCLUSIONS: The findings suggested that NFATc3 plays a role in maintaining the pancreatic ß-cell compensatory growth and gene expression in response to obesity.

Variations in the conserved 18S and 5.8S reveal the putative pseudogenes in 18S-ITS1-5.8S rDNA of Cynoglossus melampetalus (Pleuronectiformes: Cynoglossidae).

Many early studies of ribosomal RNA gene (rDNA) suggested that rDNA tandem repeats within species are homogeneous. However, increasing number of reports have found intra-individual rDNA polymorphism across a range of taxa. Here, we reported a high level of intra-individual polymorphism of 18S-ITS1-5.8S rDNA in the genome of Cynoglossus melampetalus (Pleuronectiformes: Cynoglossidae), indicating a non-concerted evolution manner. Sequence alignments found two distinct types of 18S and 5.8S (Type A and B) and five types of ITS1 sequence (Type A - E) coexisted in the genome differing in length, GC content, secondary structure stability and minimum free energy. Based on the unique features of pseudogene and comparison of the conserved 18S rDNA sequence and 5.8S secondary structure of 22 flatfishes revealed that Type B sequences of 18S, 5.8S and their linked ITS1 were putative pseudogenes. So far, detection of rRNA pseudogenes from the multiple rDNA copies has been an intricate puzzle. Our results, as a result, provide a new ideal for rRNA pseudogene identification.

Single-molecule long-read sequencing of the full-length transcriptome of Rhododendron lapponicum L.

Rhododendron lapponicum L. is a familiar ornamental plant worldwide with important ornamental and economic value. However, a full-length R. lapponicum transcriptome is still lacking. In the present study, we used the Pacific Biosciences single-molecule real-time sequencing technology to generate the R. lapponicum transcriptome. A total of 346,270 full-length non-chimeric reads were generated, from which we obtained 75,002 high-quality full-length transcripts. We identified 55,255 complete open reading frames, 7,140 alternative splicing events and 2,011 long non-coding RNAs. In gene annotation analyses, 71,155, 33,653, 30,359 and 31,749 transcripts were assigned to the Nr, GO, COG and KEGG databases, respectively. Additionally, 3,150 transcription factors were detected. KEGG pathway analysis showed that 96 transcripts were identified coding for the enzymes associated with anthocyanin synthesis. Furthermore, we identified 64,327 simple sequence repeats from 45,319 sequences, and 150 pairs of primers were randomly selected to develop SSR markers. This study provides a large number of full-length transcripts, which will facilitate the further study of the genetics of R. lapponicum.

Novel gene rearrangement pattern in Cynoglossus melampetalus mitochondrial genome: New gene order in genus Cynoglossus (Pleuronectiformes: Cynoglossidae).

Mitochondrial genome (mitogenome) structure and gene order are generally considered conserved in vertebrates. However, the flatfish (Pleuronectiformes) mitogenomes exhibit the most diversified gene rearrangement patterns. Here, we report a newly sequenced mitogenome of Cynoglossus melampetalus (Pleuronectiformes: Cynoglossidae). The total length of the C. melampetalus mitogenome is 16,651 bp, containing 13 protein-coding genes, two ribosomal RNAs, 22 transfer RNAs, a putative control region, and an L-strand replication origin. Like all previously reported tongue sole (Cynoglossinae) mitogenomes, the C. melampetalus tRNA-Gln gene is inverted from the light to the heavy strand (Q inversion), accompanied by the translocation of CR, which is downstream to the 3'-end of ND1. In addition, we observed a unique tRNA-Ile-Met-Glu (IMQ) gene order that differed from the tRNA-Glu-Ile-Met (QIM) order previously reported for other 14 Cynoglossinae mitogenomes. To our knowledge, it is the first report of two different patterns of mitogenomic gene-arrangement within the same genus in teleost. According to the Q inversion, Met pseudogene (ψMet) and long intergenic gap (186 bp) between M and Q genes, the observed gene rearrangement pattern were presumably supported by mitochondrial recombination and tandem duplication/random loss models. The reduced trend of the intergenic gap between Q and I also suggests that the event of gene rearrangement can be traced back to early Cynoglossinae differentiation.

Cathelicidin aggravates myocardial ischemia/reperfusion injury via activating TLR4 signaling and P2X7R/NLRP3 inflammasome.

AIMS: The antimicrobial peptide cathelicidin (Camp) has multifunctional immunomodulatory activities. However, its roles in inflammation-related myocardial ischemia/reperfusion (MI/R) injury remain unclear. METHODS AND RESULTS: In this study, adult male C57BL/6 wild-type (WT) mice were subjected to MI/R injury by left anterior descending coronary artery ligation for 45 min followed by 3 or 24 h of reperfusion. An abundant cardiac expression of cathelicidin was observed during ischemia and reperfusion, which was mainly derived from heart-infiltrating neutrophils. Knockout of Camp in mice reduced MI/R-induced myocardial inflammation, infarct size, and circulating cTnI levels (an indicator of heart damage). CRAMP (the mature form of murine cathelicidin) administration of WT mice immediately before MI/R exerted detrimental effects on the reperfused heart. CRAMP exacerbates MI/R injury via a TLR4 and P2X7R/NLRP3 inflammasome-dependent mechanism, since I/R-induced myocardial infarction was reserved by inhibition of TLR4, P2X7R, or NLRP3 inflammasome in CRAMP-treated WT mice. Depletion of neutrophils before MI/R abrogated the amplification of infarct size in CRAMP-treated WT mice. Heart-infiltrating neutrophils were found to be one of major cellular sources of myocardial IL-1ß (a "first line" pro-inflammatory cytokine) at the early stage of MI/R. At this stage, CRAMP administration just before MI/R induced pro-IL-1ß protein expression in heart-infiltrating neutrophils, but not in non-neutrophils. In vitro experiments showed that LL-37 (the mature form of human cathelicidin) treatment promotes the processing and secretion of IL-1ß from human neutrophils via stimulating TLR4 signaling and P2X7R/NLRP3 inflammasome. CONCLUSIONS: Our findings reveal that, at the early stage of MI/R, neutrophil-derived cathelicidin plays an injurious role in the heart. Cathelicidin aggravates MI/R injury by over-activating TLR4 signaling and P2X7R/NLRP3 inflammasome in heart-infiltrating neutrophils, which leads to the excessive secretion of IL-1ß and subsequent inflammatory injury.

Mechanisms of gene rearrangement in 13 bothids based on comparison with a newly completed mitogenome of the threespot flounder, Grammatobothus polyophthalmus (Pleuronectiformes: Bothidae).

BACKGROUND: The mitogenomes of 12 teleost fish of the bothid family (order Pleuronectiformes) indicated that the genomic-scale rearrangements characterized in previous work. A novel mechanism of genomic rearrangement called the Dimer-Mitogenome and Non-Random Loss (DMNL) model was used to account for the rearrangement found in one of these bothids, Crossorhombus azureus. RESULTS: The 18,170 bp mitogenome of G. polyophthalmus contains 37 genes, two control regions (CRs), and the origin of replication of the L-strand (OL). This mitogenome is characterized by genomic-scale rearrangements: genes located on the L-strand are grouped in an 8-gene cluster (Q-A-C-Y-S1-ND6-E-P) that does not include tRNA-N; genes found on the H-strand are grouped together (F-12S … CytB-T) except for tRNA-D that was translocated inside the 8-gene L-strand cluster. Compared to non-rearranged mitogenomes of teleost fishes, gene organization in the mitogenome of G. polyophthalmus and in that of the other 12 bothids characterized thus far is very similar. These rearrangements could be sorted into four types (Type I, II, III and IV), differing in the particular combination of the CR, tRNA-D gene and 8-gene cluster and the shuffling of tRNA-V. The DMNL model was used to account for all but one gene rearrangement found in all 13 bothid mitogenomes. Translocation of tRNA-D most likely occurred after the DMNL process in 10 bothid mitogenomes and could have occurred either before or after DMNL in the three other species. During the DMNL process, the tRNA-N gene was retained rather than the expected tRNA-N' gene. tRNA-N appears to assist in or act as OL function when the OL secondary structure could not be formed from intergenic sequences. A striking finding was that each of the non-transcribed genes has degenerated to a shorter intergenic spacer during the DMNL process. These findings highlight a rare phenomenon in teleost fish. CONCLUSIONS: This result provides significant evidence to support the existence of dynamic dimeric mitogenomes and the DMNL model as the mechanism of gene rearrangement in bothid mitogenomes, which not only promotes the understanding of mitogenome structural diversity, but also sheds light on mechanisms of mitochondrial genome rearrangement and replication.