Genome-wide identification and structural analysis of the BMP gene family in Triplophysa dalaica.

BACKGROUND: Bone morphogenetic proteins (BMPs) are part of the transforming growth factor beta (TGF-ß) superfamily and play crucial roles in bone development, as well as in the formation and maintenance of various organs. Triplophysa dalaica, a small loach fish that primarily inhabits relatively high elevations and cooler water bodies, was the focus of this study. Understanding the function of BMP genes during the morphogenesis of T. dalaica helps to clarify the mechanisms of its evolution and serves as a reference for the study of BMP genes in other bony fishes. The data for the T. dalaica transcriptome and genome used in this investigation were derived from the outcomes of our laboratory sequencing. RESULTS: This study identified a total of 26 BMP genes, all of which, except for BMP1, possess similar TGF-ß structural domains. We conducted an analysis of these 26 BMP genes, examining their physicochemical properties, subcellular localization, phylogenetic relationships, covariance within and among species, chromosomal localization, gene structure, conserved motifs, conserved structural domains, and expression patterns. Our findings indicated that three BMP genes were associated with unstable proteins, while 11 BMP genes were located within the extracellular matrix. Furthermore, some BMP genes were duplicated, with the majority being enriched in the GO:0008083 pathway, which is related to growth factor activity. It was hypothesized that genes within the BMP1/3/11/15 subgroup (Group I) play a significant role in the growth and development of T. dalaica. By analyzing the expression patterns of proteins in nine tissues (gonad, kidney, gill, spleen, brain, liver, fin, heart, and muscle), we found that BMP genes play diverse regulatory roles during different stages of growth and development and exhibit characteristics of division of labor. CONCLUSIONS: This study contributes to a deeper understanding of BMP gene family member expression patterns in high-altitude, high-salinity environments and provides valuable insights for future research on the BMP gene family in bony fishes.

The Role of Introgression During the Radiation of Endemic Fishes Adapted to Living at Extreme Altitudes in the Tibetan Plateau.

Recent genomic analyses of evolutionary radiations suggest that ancient introgression may facilitate rapid diversification and adaptive radiation. The loach genus Triplophysa, a genus with most species endemic to Tibetan Plateau, shows ecological diversity and rapid evolution and represents a potential example of adaptive radiation linked to the uplift of the Tibetan Plateau. Here, we interrogate the complex evolutionary history of Triplophysa fishes through the analysis of whole-genome sequences. By reconstructing the phylogeny of Triplophysa, quantifying introgression across this clade, and simulating speciation and migration processes, we confirm that extensive gene flow events occurred across disparate Triplophysa species. Our results suggest that introgression plays a more substantial role than incomplete lineage sorting in underpinning phylogenetic discordance in Triplophysa. The results also indicate that genomic regions affected by ancient gene flow exhibit characteristics of lower recombination rates and nucleotide diversity and may associate with selection. Simulation analysis of Triplophysa tibetana suggests that the species may have been affected by the Gonghe Movement in the third uplift of the Tibetan Plateau, resulting in founder effects and a subsequent reduction in Ne.

Environmental DNA unveils deep phylogeographic structure of a freshwater fish.

Phylogeography bears an important part in ecology and evolution. However, current phylogeographic studies are largely constrained by limited numbers of individual samples. Using an environmental DNA (eDNA) assay for phylogeographic analyses, this study provides detailed information regarding the history of Siberian stone loach Barbatula toni, a primary freshwater fish across the whole range of Hokkaido, Japan. Based on an eDNA metabarcoding on 293 river water samples, we detected eDNA from B. toni in 189 rivers. A total of 51 samples, representing the entire island, were then selected from the B. toni eDNA-positive sample set for the subsequent analyses. To elucidate the phylogeographic structure of B. toni, newly developed eDNA metabarcoding primers (Barba-cytb-F/R) were applied to these samples, specifically targeting their haplotypic variation in cytochrome b. After a bioinformatic processing to mitigate haplotypic false positives, a total of 50 eDNA haplotypes were identified. Two regionally restricted, genetically distinct lineages of the species were revealed as a result of phylogeographic analyses on the haplotypes and tissue-derived DNA from B. toni. According to a molecular clock analysis, they have been genetically isolated for at least 1.5 million years, suggesting their ancient origin and colonisation of Hokkaido, presumably in the glacial periods. These results demonstrate how freshwater fishes can alter their distributions over evolutionary timescales and how eDNA assay can deepen our understanding of phylogeography.

Ecological genetics of isolated loach populations indicate compromised adaptive potential.

Many endangered species live in fragmented and isolated populations with low genetic variability, signs of inbreeding, and small effective population sizes - all features elevating their extinction risk. The flat-headed loach (Oreonectes platycephalus), a small noemacheilid fish, is widely across southern China, but only in the headwaters of hillstreams; as a result, they are spatially isolated from conspecific populations. We surveyed single nucleotide polymorphisms in 16 Hong Kong populations of O. platycephalus to determine whether loach populations from different streams were genetically isolated from each other, showed low levels of genetic diversity, signs of inbreeding, and had small contemporary effective population sizes. Estimates of average observed heterozygosity (HO = 0.0473), average weighted nucleotide diversity (πw = 0.0546) and contemporary effective population sizes (Ne = 10.2 ~ 129.8) were very low, and several populations showed clear signs of inbreeding as judged from relatedness estimates. The degree of genetic differentiation among populations was very high (average FST = 0.668), even over short geographic distances (<1.5 km), with clear patterns of isolation by distance. These results suggest that Hong Kong populations of O. platycephalus have experienced strong genetic drift and loss of genetic variability because sea-level rise after the last glaciation reduced connectedness among paleodrainages, isolating populations in headwaters. All this, together with the fact that the levels of genetic diversity and contemporary effective population sizes within O. platycephalus populations are lower than most other freshwater fishes, suggests that they face high local extinction risk and have limited capacity for future adaptation.

Damage of polyethylene microplastics on the intestine multilayer barrier, blood cell immune function and the repair effect of Leuconostoc mesenteroides DH in the large-scale loach (Paramisgurnus dabryanus).

Polyethylene microplastics (PE-MPs) has become a global concern due to their widespread distribution and hazardous properties in aquatic habitats. In this study, the accumulation effect of PE-MPs in the intestine of large-scale loach (Paramisgurnus dabryanus) was explored by adding different concentrations of PE-MPs to the water, the destination of PE-MPs after breaking the intestinal barrier and the effects caused. The collected data showed that PE-MPs accumulation for 21d altered the histomorphology and antioxidant enzyme activity of the intestine, induced dysbiosis of the intestinal flora. 10 mg/L of PE-MPs induced a significant increase in the transcript levels of intestinal immunity factors in loach after 21d of exposure. Moreover, the levels of diamine oxidase (DAO) and d-lactic acid (D-Lac) in the gut and serum of loach were significantly increased after exposure to PE-MPs at all concentrations (1, 5, 10 mg/L). Subsequently, the presence of PE-MPs was detected in the blood, suggesting that the disruption of the intestinal multilayer barrier allowed PE-MPs to spill into the circulation. The accumulation of PE-MPs (1,5,10 mg/L) in the blood led to massive apoptosis and necrosis of blood cells and activated phagocytosis in response to PE-MPs invasion. To alleviate the damage, this study further exposure the effect of probiotics on PE-MPs treated loach by adding Leuconostoc mesenteroides DH (109 CFU/g) to the feed. The results showed that DH significantly increased the intestinal index and reduced the levels of DAO and D-Lac. To investigate the reason, we followed the PE-MPs in the intestine and blood of the loach and found that the number of PE-MPs particles was significantly reduced in the probiotic group, while the PE-MPs content in the feces was elevated. Thus, we concluded that DH reducing the accumulation of PE-MPs in the intestinal by increases fecal PE-MPs, which in turn mitigates the damage to the intestinal barrier caused by PE-MPs, and reduces the amount of PE-MPs in the blood. This work offers a robust analysis to understand the mechanisms of damage to the intestinal barrier by MPs and the fate of MPs after escaping the intestinal barrier and provide a new perspective on the application of probiotics in mitigating PE-MPs toxicity.

A New Species of the Blind Cave Loach Genus Protocobitis (Cypriniformes: Cobitidae), Protocobitis longicostatus sp. nov., from Guangxi, China.

Protocobitis species are typical cave-dwelling fish, exhibiting distinctive morphological adaptations such as colorless body, lack of eyes, and reduced scales and ribs in response to their extreme cave habitats. Distinct from the recorded species, P. anteroventris, P. polylepis, and P. typhlops, a new species, Protocobitis longicostatus sp. nov., is described from Guangxi Zhuang Autonomous Region, China. Protocobitis longicostatus sp. nov. can easily be distinguished from all known congeners by the following characteristics: whole body covered by scales except head, 12 branched caudal fin rays, and long ribs. These species face threats from habitat degradation, hydrological changes, and environmental pollution. Thus, the conservation of cavefish in China has become an urgent issue.

Effect of Hypoxia on the Gut Microflora of a Facultative Air-Breathing Loach Lepidocephalichthys guntea.

One of the main risks to fish health in an aquatic environment is hypoxia, which can either lead to respiratory failure or the emergence of various diseases in a fish population. This investigation examined the impact of hypoxia on the gut bacteria of a loach, Lepidocephalichthys guntea, which under the dissolve oxygen stress can gulp air from surface and breathe using its posterior intestine. High-throughput sequencing was used to examine the anterior and posterior parts of the gut of L. guntea during both normoxia and hypoxia. According to the community profiling of the gut bacteria, prolonged exposure to hypoxia increased the diversity and abundance of bacteria in the posterior part while decreasing both in the anterior part of the gut. Additionally, for both parts of the gut, the core microbiota showed a significant alteration during hypoxia. In correlation network analysis, a more interactive and intricate network was developed at normoxia. According to the comparative analyses of the gut bacteria, hypoxia causes more pronounced alterations in the posterior gut than the anterior gut at various taxonomic levels. As a consequence of hypoxia, several genera like Aeromonas, Pseudomonas, Plesiomonas, Acinetobacter, and Enterobacter were replaced by Streptococcus, Escherichia-Shigella, Janthinobacterium, and Clostridia. A surge in probiotic genera, including Bifidobacterium, Lactobacillus, Blautia, and Cetobacterium, was also seen. The fatty acid biosynthesis pathway was induced only in hypoxia, although all other metabolic pathways were present in both situations, albeit with fewer hits in hypoxia.

Effects of fasting and environmental factors on appetite regulators in pond loach Misgurnus anguillicaudatus.

The pond loach (Misgurnus anguillicaudatus) is an important aquaculture freshwater species, used as an ornamental fish, food source for humans and angling bait. Pond loaches are resistant to fasting and extreme environmental conditions, including temperature and low oxygen levels. Little is known about how these factors affect the feeding physiology and the endocrine regulation of feeding of loaches. In this study, we examined the effects of fasting, as well as increased temperature and decreased oxygen levels on food intake and transcript levels of appetite regulators. Fasted fish had lower blood glucose levels, and lower expression levels of intestine CCK and PYY, and brain CART1, but had higher levels of brain orexin and ghrelin than fed fish. Fish held at 30 °C had higher food intake, glucose levels, and mRNA levels of intestine CCK and PYY, and brain CART2, but lower brain orexin levels than fish at 20 °C. Fish held at low oxygen levels had a lower food intake, higher intestine CCKa and ghrelin, and brain orexin, CART2 and ghrelin mRNA expression levels than fish held at high O2 levels. Our results suggest that fasting and high temperatures increase the expression of orexigenic and anorexigenic factors respectively, whereas the increase in expression of both orexigenic and anorexigenic factors in low O2 environments might not be related to their role in feeding, but possibly to protection from tissue damage. The results of our study might shed new light on how pond loaches are able to cope with extreme environmental conditions such as low food availability, extreme temperatures and hypoxia.

Rh proteins and H+ transporters involved in ammonia excretion in Amur Ide (Leuciscus waleckii) under high alkali exposure.

High alkaline environment can lead to respiratory alkalosis and ammonia toxification to freshwater fish. However, the Amur ide (Leuciscus waleckii), which inhabits an extremely alkaline lake in China with titratable alkalinity up to 53.57 mM (pH 9.6) has developed special physiological and molecular mechanisms to adapt to such an environment. Nevertheless, how the Amur ide can maintain acid-base balance and perform ammonia detoxification effectively remains unclear. Therefore, this study was designed to study the ammonia excretion rate (Tamm), total nitrogen accumulation in blood and tissues, including identification, expression, and localization of ammonia-related transporters in gills of both the alkali and freshwater forms of the Amur ide. The results showed that the freshwater form Amur ide does not have a perfect ammonia excretion mechanism exposed to high-alkaline condition. Nevertheless, the alkali form of Amur ide was able to excrete ammonia better than freshwater from Amur ide, which was facilitated by the ionocytes transporters (Rhbg, Rhcg1, Na+/H+ exchanger 2 (NHE2), and V-type H+ ATPase (VHA)) in the gills. Converting ammonia into urea served as an ammonia detoxication strategy to reduced endogenous ammonia accumulation under high-alkaline environment.

Scale Characteristics of Six Fish Species of the Genus Cyprinion (Teleostei: Cypriniformes): A Microscopic Analysis.

This study investigated the morphological characteristics of scales in six Cyprinion species, using light and scanning electron microscopy focusing on key features such as scale type, key scales, lateral line scales, radius/radii, rostral margin, focus, circuli, lepidonts, tubercles, and scale indices. The research analyzed the scales using ultramicroscopy and light microscopy imaging, categorizing them based on size classes and body regions. The morphological variations in scale characteristics were examined across different species, regions, and size classes. Notable findings included the tetra-sectioned form of scales, representing a unique characteristic of the Cyprinion genus. Morphological changes in scale features were observed with fish growth, particularly in the overall shape, focus shape, and size. Quantitative analysis revealed variations in average relative scale length and width among different species, regions, and size classes. The study utilized canonical discriminant analysis for multivariate assessment, classifying the species into distinct groups based on morphometric indices. The findings contribute to the understanding of scale morphology in Cyprinion species and exploring morphological variation between the examined species.

The chromosome-level genome and key genes associated with mud-dwelling behavior and adaptations of hypoxia and noxious environments in loach (Misgurnus anguillicaudatus).

BACKGROUND: The loach (Misgurnus anguillicaudatus), the most widely distributed species of the family Cobitidae, displays a mud-dwelling behavior and intestinal air-breathing, inhabiting the muddy bottom of extensive freshwater habitats. However, lack of high-quality reference genome seriously limits the interpretation of the genetic basis of specialized adaptations of the loach to the adverse environments including but not limited to the extreme water temperature, hypoxic and noxious mud environment. RESULTS: This study generated a 1.10-Gb high-quality, chromosome-anchored genome assembly, with a contig N50 of 3.83 Mb. Multiple comparative genomic analyses found that proto-oncogene c-Fos (fos), a regulator of bone development, is positively selected in loach. Knockout of fos (ID: Mis0086400.1) led to severe osteopetrosis and movement difficulties, combined with the comparison results of bone mineral density, supporting the hypothesis that fos is associated with loach mud-dwelling behavior. Based on genomic and transcriptomic analysis, we identified two key elements involved in the intestinal air-breathing of loach: a novel gene (ID: mis0158000.1) and heat shock protein beta-1 (hspb1). The flavin-containing monooxygenase 5 (fmo5) genes, central to xenobiotic metabolism, undergone expansion in loach and were identified as differentially expressed genes in a drug stress trial. A fmo5-/- (ID: Mis0185930.1) loach displayed liver and intestine injury, indicating the importance of this gene to the adaptation of the loach to the noxious mud. CONCLUSIONS: Our work provides valuable insights into the genetic basis of biological adaptation to adverse environments.

Turcinoemacheilus ekmekciae, a new dwarf loach from upper Tigris and Euphrates (Teleostei: Nemacheilidae).

Turcinoemacheilus ekmekciae, new species, from upper Euphrates and Tigris drainages is distinguished from other species of Turcinoemacheilus in Western Asia by having a dark stripe broader than the eye diameter along the lateral line, rarely possessing roundish blotches, 5-6 mandibular pores in mandibular canal, a comperatvely smaller head, a deeper body, and a greater pre-pelvic distance. Our specimens collected from the upper Great Zab, near the type locality of Turcinoemacheilus kosswigi, showed notable genetic divergence (a minimum K2P of 3.3%) from sequences reported as T. kosswigi in previous studies. Despite morphological similarities, this molecular difference suggests that the populations analysed in previous studies may represent a potential new species of Turcinoemacheilus, which we tentatively named as Turcinoemacheius cf. kosswigi. Molecular data also suggest that T. ekmekciae is characterized by a minimum K2P distance of 3.5% from Turcinoemacheilus minimus and T. cf. kosswigi. The three methods for species delimitation (assemble species by automatic partitioning [ASAP], Poisson tree processes [PTP], and multi-rate PTP [mPTP]) that were utilized for testing species assignments consistently identified our test group as a distinct species.

Descriptions of two new species of the botiid genus Leptobotia Bleeker, 1870 (Teleostei: Cypriniformes) from South China.

Two new species of Leptobotia are here described as L. rotundilobus from the Xin'an-Jiang of the upper Qiantang-Jiang basin in both Anhui and Zhejiang Provinces and the Cao'e-Jiang in Zhejiang Province, and L. paucipinna from the Qing-Jiang of the middle Chang-Jiang basin in Hubei Province, South China. Both have a plain brown body as found in L. bellacauda Bohlen & Slechtová, 2016, L. microphthalma Fu & Ye, 1983, L. posterodorsalis Chen & Lan, 1992 and L. tientainensis (Wu, 1930). The two new species are distinct from these species in vertebral counts, further from L. posterodorsalis in vent placement and further from the other three species in pectoral-fin length. Both differ in caudal-fin coloration and shape, and dorsal-fin location and coloration, and also in internal morphology. Their validity is confirmed by their own monophyly recovered in a phylogenetic analysis based on the mitochondrial cyt b and COI genes.

First record of intraspecific cleaning behavior by the threatened Leuciscidae Squalius alburnoides (Steindachner, 1866) at the Guadiana River basin (Portugal).

Squalius alburnoides (Steindachner, 1866) is an endemic threatened species from the Iberian Peninsula. Here, we report the first observations of intraspecific cleaning behavior in isolated summer pools in the Guadiana River Basin (Portugal). We found that focal S. alburnoides solicited cleaning by adopting an immobile tail-stand position known as "posing," which immediately signaled a response to a few conspecifics that approached and inspect them. Our study expands the list of cleanerfish species in freshwaters, giving emphasis to the importance of mutual positive behavior within an endangered species, particularly when facing seasonal disturbance.

Schistura sonarengaensis, a new species of cave-dwelling loach (Teleostei: Nemacheilidae) from Meghalaya, northeast India.

A new species of nemacheilid loach, Schistura sonarengaensis sp. nov., is described from three cave-dwelling populations (Barak-Surma-Meghna drainage) in the South Garo Hills district of Meghalaya, India. The new species possesses prominent eyes but is easily distinguished from all the congeners of the genus Schistura from Barak-Surma-Meghna and adjacent rivers drainages of northeast Indian (except S. syngkai) in having 13-26 vertically elongated to circular mid-lateral black blotches (brownish in life) overlayered on a grayish-black mid-lateral stripe on a dull white or pale-beige (golden brown in life) body. However, it can be easily distinguished from S. syngkai in having a complete (vs. incomplete) lateral line with more 72-89 (vs. 19-42) lateral-line pored scales, greater pre-dorsal length (48.5-53.1 vs. 41.9-44.1 %SL), a wider body at dorsal-fin origin (11.3-16.7 vs. 9.4-10.3 %SL), greater dorsal (18.1-21.1 vs. 15.1-17.0 %SL) and lateral (20.9-24.1 vs. 17.4-18.9 %SL) head length, a wider head (14.5-18.5 vs. 11.6-13.3 %SL), and moderately forked (vs. emarginated) caudal fin. Further, molecular analysis confirms the distinctiveness of S. sonarengaensis sp. nov. from its congeners found in northeast India by significant divergences with uncorrected genetic distance ranging from 3.7% to 17.3% in the mitochondrial cytochrome c oxidase subunit I (COI) gene dataset. The phylogenetic position of the new species with its sister species was evaluated using maximum likelihood and Bayesian analysis. The species delimitation approaches assemble species by automatic partitioning (ASAP) and Poisson tree processes (PTP) utilized for testing species assignments consistently identified our test group as a distinct species from its sister species. Although the new species lacks typical morphological adaptations usually associated with a subterranean life, such as complete absence (or vestigial presence) of eyes and pigmentation, it exhibits a reduction of pigmentation when compared to the epigean congeners.

Contrasting genetic and morphological differentiation among geographical lineages of a stenotopic miniature rasborine, Boraras maculatus, in Peninsular Malaysia.

The variability in the stenotopic miniature rasborine Boraras maculatus (Cypriniformes: Danionidae: Rasborinae) across acidic-water habitats of Peninsular Malaysia (PM) was investigated using two molecular markers (the mitochondrial cytochrome c oxidase subunit I [COI] gene and the nuclear rhodopsin gene), as well as morphological evidence. Molecular phylogenetic analyses revealed differentiation among populations of B. maculatus in PM with the distinction of four allopatric lineages. Each of them was recognized as a putative species by automatic species delimitation methods. These lineages diverged from each other between 7.4 and 1.9 million years ago. A principal component analysis (PCA) was conducted to examine the multivariate variation in 11 morphometric measurements among three of these lineages. PCA results showed a significant overlap in morphological characteristics among these lineages. Additionally, a photograph-based machine learning approach failed to fully differentiate these lineages, suggesting limited morphological differentiation. B. maculatus represents a case of morphological stasis in a stenotopic miniature species. Strong habitat preference, coupled with long-term habitat fragmentation, may explain why each lineage of B. maculatus has a restricted distribution and did not disperse to other regions within and outside of PM, despite ample possibilities when the Sunda shelf was emerged and drained by large paleodrainages for most of the past 7 million years. The conservation status of B. maculatus and its peat swamp habitats are discussed, and it is concluded that peat swamps comprise several evolutionary units. Each of these units is considered a conservation unit and deserves appropriate protection.

A new cavefish of Sinocyclocheilus (Teleostei: Cypriniformes: Cyprinidae) from the Nanpanjiang River in Guizhou, China.

A new species, Sinocyclocheilus xingyiensis, is described based on specimens collected from a karst cave in Guizhou Province, China. The authors used an integrated taxonomic approach, including morphological and molecular data, to identify the new species as a member of the Sinocyclocheilu angularis group, and it can be distinguished from all other members of this group by a combination of the following features: two pairs of long barbels and long pectoral fins, 42-46 lateral-line scales, 7 (13-14) on outer (inner) side of the first gill arch and 35 (14-15 + 4 + 16 - 17) vertebrae. Phylogenetic analyses based on the cytochrome b (cyt b) gene fragment suggest that S. xingyiensis is a sister lineage to Sinocyclocheilus flexuosdorsalis. The genetic distance (Kimura 2-parameter) between the S. xingyiensis and S. angularis groups of Sinocyclocheilus species based on cyt b gene fragment ranged from 1.2% to 15.4%.

Molecular characterization, spatiotemporal expression, and background adaptation regulation of tyrosinase in loach (Misgurnus anguillicaudatus).

The Poyang Lake region is home to large-blackspot loaches (LBL), small-blackspot loaches (SBL), and non-blackspot loaches (NBL), Misgurnus anguillicaudatus. To investigate the impact of tyrosinase on spot development, the complementary DNAs (cDNA) of tyrosinase in M. anguillicaudatus (designated as Matyr) were cloned using the rapid amplification of cDNA ends (RACE)-PCR method. The full-length cDNA for Matyr was 2020 bp, and the open-reading frame comprised 1617 bp, encoding a predicted protein with 538 amino acids. Phylogenetic studies revealed that MaTyr was first grouped with Tyr of Triplophysa tibetana and Leptobotia taeniops, and then Tyr of other cyprinid fish. The quantitative reverse-transcription-PCR results show that Matyr was highly expressed in the muscle, caudal fin, and dorsal skin. The Matyr gene's messenger RNA expression pattern steadily increased from the fertilized ovum period to the somitogenesis period, and from the muscle effect stage to 6 days after fertilization, it considerably increased (p < 0.01). The Matyr hybridization signals with similar location could be found in all developmental stages of three kinds of loaches using whole-mount in situ hybridization (WISH) technology and were the strongest during the organ development period and melanin formation period. Dot hybridization signals in LBLs rapidly spread to the back of the body beginning at the period when the eyes first formed melanin, and their dimensions were larger than those of NBLs during the same time period. The body color of loaches could change reversibly with black/white background adaptation. The α-msh, mitfa, and tyr are mainly expressed in loaches adapted with a black background. Tyr gene could be involved in the development of blackspots and body color polymorphism, and contribute to organ development in the loach.

Transcriptome analysis of Schizothorax oconnori (Cypriniformes: Cyprinidae) oocytes: The role of K+ in promoting yolk globule fusion and regulating oocyte maturation.

Schizothorax oconnori (S. oconnori) is an economically important fish in Tibet. Oocyte maturation is a physiological process that is of great significance to reproduction and seed production in S. oconnori, yet little is currently known regarding the molecular mechanisms of oocyte development in this species. To identify candidate genes involved in reproduction of female fish, a combination of PacBio and Illumina HiSeq technologies was employed to provide deep coverage of the oocyte transcriptome. Transcriptome analysis revealed several candidate genes that are potentially involved in the regulation of oocyte maturation in S. oconnori, including GIRK1, CHRM3, NPY2R, GABRA3, GnRH3, mGluR1α, GPER1, GDF9, HSP90, and ESR2. Genes that are significantly expressed during oocyte maturation mainly contribute to the GPCR signaling pathway and the estrogen signaling pathway. Neurotransmitter (Ach, NPY, and GABA) and peptide hormone (GnRH3) binding to G protein-coupled receptors (GPCRs) frees G-protein ßγ subunits to interact with the G protein-gated inward rectifier K+ channel 1 (GIRK1). This process helps release K+ from granulosa cells to maturing oocytes, allowing yolk globule fusion. This mechanism may play an important role in oocyte maturation in S. oconnori. In conclusion, this study provides a valuable basis for deciphering the reproductive system in S. oconnori during the oocyte maturation process.

Genetic characterization, structural analysis, and detection of positive selection in small heat shock proteins of Cypriniformes and Clupeiformes.

In the current investigation, a total of 42 full-length, non-redundant small heat shock proteins (sHsp) were detected in Cyprinus carpio, Labeo rohita, Danio rerio, Salmo salar, Oncorhynchus mykiss, and Clupea harengus. The sHsp genes were classified into three groups based on phylogenetic analysis. All the sHsps were shown to have higher aliphatic index values, which is an indication that these proteins are more thermally stable. The hydrophilic nature of sHsps was deduced from the fact that all fish species had negative GRAVY scores. In all of the representative fish species, sHsp genes were assigned to distinct chromosomes in an inconsistent and unequal manner. Segmental duplications are the main events that have contributed to the expansion of the sHsp genes in all species. We were also able to determine the selective pressure that was placed on particular codons and discovered several significant coding sites within the coding region of sHsps. Eventually, diversifying positive selection was found to be connected with evolutionary changes in sHsp proteins, which showed that gene evolution controlled the fish adaption event in response to environmental conditions. Clarification of the links between sHsps and environmental stress in fish will be achieved through rigorous genomic comparison, which will also yield substantial new insights.