Transcriptome analysis of Clarias magur brain and gonads suggests neuro-endocrine inhibition of milt release from captive GnRH-induced males

Characterization of Kiss/Kissr system and expression profiling through developmental stages indicate kiss1 to be the active isotype in Clarias magur

Kisspeptin (Kiss) and kisspeptin receptor (Kissr) system is a key regulator of GnRH expression in several vertebrates. The Indian catfish, Clarias magur, is popular in the Indian sub-continent, and a neo-type of the Asian catfish, C. batrachus. Catfish breeding is constrained as males do not release milt captivity with/without stimulation. Magur Kiss/Kissr system comprising of kiss1, kiss2, kissr1, and kissr2 genes was characterized for the first time. Full-length mRNA was sequenced using RACE PCR. Neighbor-joining tree of predicted proteins shows one clade of teleost orthologs. Magur whole genome (NCBI GenBank) has single copies of each gene, though yet unannotated/misannotated. Anomalies in the nomenclature of earlier sequences in GenBank were noted. Relative gene expression was profiled during various ontogenic stages, in six tissues including brain and gonads at maturity, and also in brains and gonads of premature and spent fish. Expression of gnrh1, gnrhr1, and gnrhr2 was estimated concomitantly. The kiss1 was the first to be twofold upregulated (P < 0.05) at 12 h post fertilization. Kiss/Kissr genes expressed primarily in the brain, ovary, and testis. Though kiss2 was 10 times higher than kiss1, only kiss1 showed significant modulation across stages and appears to be the active isotype that regulates GnRH in magur.

Cloning, computational analysis and expression profiling of steroid 5 alpha-reductase 1 (SRD5A1) gene during reproductive phases and ovatide stimulation in endangered catfish, Clarias magur

The cloning and characterization of the complete coding sequence of the Clarias magur SRD5A1 (CmSRD5A1) gene, which encodes an enzyme responsible for regulating steroid levels by converting testosterone into 5α-dihydrotestosterone (DHT), have been successfully achieved. DHT plays a vital role in enabling the complete expression of testosterone's actions in neuroendocrine tissues. The ORF of the full-length cDNA sequence of SRD5A1 was 795 bp, translating into 265 amino acids, with a total length of 836 bp including UTRs. Like other vertebrates, the signal peptide analysis revealed that SRD5A1 is a non-secretory protein, and hydropathy profiles indicated that it is hydrophobic in nature. The 3D structure of CmSRD5A1 sequence generated above was predicted using highly accurate AlphaFold 2 in Google Colab online platform. CmSRD5A1 contains seven transmembrane helices connected by six loops, with the N-termini located on the periplasmic side and C-termini on the cytosolic side. Structural superimposition with known bacterial and human SRD5As showed very high structural similarity. The electrostatic potential calculation and surface analysis of CmSRD5A1 revealed the presence of a large cavity with two openings one highly electropositive towards the cytosolic side and another relatively neutral towards the transmembrane region. The structural comparison revealed that the electropositive side of the cavity should bind to NADPH and the steroid hormone in the hydrophobic environment. Polar residues binding to NADPH are highly conserved and the same as known strictures. The conserved residues involved in hydrogen bonding with the ketone group at C-3 in the steroids hence fevering Δ4 double-bond reduction are identified as E66 and Y101. Our findings showed that SRD5A1 expression was lower during the spawning phase than the preparatory phase in female fish, while the administration of Ovatide (a GnRH analogue) resulted in up-regulation of expression after 6 h of injection in the ovary. In males, the lowest expression was observed during the preparatory phase and peaked at 16 h post- Ovatide injection in the testis. The expression of SRD5A1 in the brain of female fish was slightly higher during the Ovatide stimulation phase than the spawning phase. This study represents the first report on the cloning and characterization of the full-length cDNA of SRD5A1 in Indian catfish.

Overcoming taxonomic challenges in DNA barcoding for improvement of identification and preservation of clariid catfish species

DNA barcoding without assessing reliability and validity causes taxonomic errors of species identification, which is responsible for disruptions of their conservation and aquaculture industry. Although DNA barcoding facilitates molecular identification and phylogenetic analysis of species, its availability in clariid catfish lineage remains uncertain. In this study, DNA barcoding was developed and validated for clariid catfish. 2,970 barcode sequences from mitochondrial cytochrome c oxidase I (COI) and cytochrome b (Cytb) genes and D-loop sequences were analyzed for 37 clariid catfish species. The highest intraspecific nearest neighbor distances were 85.47%, 98.03%, and 89.10% for COI, Cytb, and D-loop sequences, respectively. This suggests that the Cytb gene is the most appropriate for identifying clariid catfish and can serve as a standard region for DNA barcoding. A positive barcoding gap between interspecific and intraspecific sequence divergence was observed in the Cytb dataset but not in the COI and D-loop datasets. Intraspecific variation was typically less than 4.4%, whereas interspecific variation was generally more than 66.9%. However, a species complex was detected in walking catfish and significant intraspecific sequence divergence was observed in North African catfish. These findings suggest the need to focus on developing a DNA barcoding system for classifying clariid catfish properly and to validate its efficacy for a wider range of clariid catfish. With an enriched database of multiple sequences from a target species and its genus, species identification can be more accurate and biodiversity assessment of the species can be facilitated.

Protein-protein networks analysis of differentially expressed genes unveils the key phenomenon of biological process with respect to reproduction in endangered catfish, C. Magur

Clarias magur (magur) is an important freshwater catfish with high potential in the aquaculture sector in its geographical ranges of distribution. One of the impediments to realise its full aquaculture potential is the lack of understanding key genes involved in its reproduction pathways. Nonetheless, very limited information is available on brain and gonads, with respect to reproduction related issues of magur at molecular level. The present study was aimed at understanding the interaction of the brain-gonad system by analysing differentially expressed genes (DEG) in brains and gonads of male and female magur using a protein-protein network interaction study. In brief, 641, 541, 225 and 245 DEGs, respectively, in ovary, testis and female brain and male-brain of magur were used as input in String database 11.0 and Cytoscape v 3.8.0 plug-in Network Analyzer for PPI network construction followed by network superimposition, network merging and analysis. A total of 13 key genes in female brain & ovary and 12 key genes in male brain & testis were obtained based on the network topological parameter betweenness centrality and nodes degree. Among them, cyp19a1b and amh genes in male brain-testis and Tp53 and exo1 genes in female brain-ovary were identified as hub genes having a high level of interaction and expression with other key genes in the network. Further, functional annotation study of these genes revealed their active involvement in important pathways related to reproduction. This is the first report exploring the interaction of brain and gonads in the regulation of magur reproduction through a protein-protein interaction network. The 25 key genes identified in the combined network are involved in various pathways, like neuropeptide signalling pathway, oxytocin receptor-mediated signalling pathway, corticotrophin-releasing factor receptor signalling pathway and reproduction process, which could lead to a better understanding of the magur reproductive system.

Bioinformatics approaches and big data analytics opportunities in improving fisheries and aquaculture

Aquaculture has witnessed an excellent growth rate during the last two decades and offers huge potential to provide nutritional as well as livelihood security. Genomic research has contributed significantly toward the development of beneficial technologies for aquaculture. The existing high throughput technologies like next-generation technologies generate oceanic data which requires extensive analysis using appropriate tools. Bioinformatics is a rapidly evolving science that involves integrating gene based information and computational technology to produce new knowledge for the benefit of aquaculture. Bioinformatics provides new opportunities as well as challenges for information and data processing in new generation aquaculture. Rapid technical advancements have opened up a world of possibilities for using current genomics to improve aquaculture performance. Understanding the genes that govern economically relevant characteristics, necessitates a significant amount of additional research. The various dimensions of data sources includes next-generation DNA sequencing, protein sequencing, RNA sequencing gene expression profiles, metabolic pathways, molecular markers, and so on. Appropriate bioinformatics tools are developed to mine the biologically relevant and commercially useful results. The purpose of this scoping review is to present various arms of diverse bioinformatics tools with special emphasis on practical translation to the aquaculture industry.

BAC-FISH Based Physical Map of Endangered Catfish Clarias magur for Chromosome Cataloguing and Gene Isolation through Positional Cloning

Construction of a physical chromosome map of a species is important for positional cloning, targeted marker development, fine mapping of genes, selection of candidate genes for molecular breeding, as well as understanding the genome organization. The genomic libraries in the form of bacterial artificial chromosome (BAC) clones are also a very useful resource for physical mapping and identification and isolation of full-length genes and the related cis acting elements. Some BAC-FISH based studies reported in the past were gene based physical chromosome maps of Clarias magur (magur) to understand the genome organization of the species and to establish the relationships with other species in respect to genes' organization and evolution in the past. In the present study, we generated end sequences of the BAC clones and analyzed those end sequences within the scaffolds of the draft genome of magur to identify and map the genes bioinformatically for each clone. A total of 36 clones mostly possessing genes were identified and used in probe construction and their subsequent hybridization on the metaphase chromosomes of magur. This study successfully mapped all 36 specific clones on 16 chromosome pairs, out of 25 pairs of magur chromosomes. These clones are now recognized as chromosome-specific makers, which are an aid in individual chromosome identification and fine assembly of the genome sequence, and will ultimately help in developing anchored genes' map on the chromosomes of C. magur for understanding their organization, inheritance of important fishery traits and evolution of magur with respect to channel catfish, zebrafish and other species.

Evaluation of the Binding Affinity of a Gonadotropin-Releasing Hormone Analogue (GnRH-a) Buserelin through In silico and In vivo Testing in Clarias magur

Aim:

To evaluate the binding affinity and biological potency of gonadotropin-releasing hormone analogue (GnRHa) Buserelin (C60H86N16O13) based on in silico and in vivo testing for induced breeding in Clarias magur.

Background:

Many attempts have been made to induce C. magur, but encouraging results have not yet been achieved. Hence, it is the need of the hour to find out more potent analogues or other bio-molecules for induced breeding in C. magur to facilitate sustainable aquaculture.

Objective:

To determine the binding affinity of C. magur GnRH receptor through in silico and to validate it for induced breeding of C. magur.

Methods:

Buserelin (C60H86N16O13) was selected as the potential GnRHa after screening several peptides for their binding energy with the C. magur GnRH receptor. The induced breeding trial was set up at ICAR-CIFE Powarkheda Centre, M.P. India, and Buserelin was administered in different doses to the brooders along with the dopamine inhibitor domperidone. The standard treatment with the commercial salmon GnRH (sGnRH) analogue Ovaprim® (Syndel, USA) was used as the control.

Results:

The 3-D structure of C. magur GnRH receptor was generated using MODELLER software. Molecular docking studies revealed the binding preference of the receptor as chicken (c) Gn- RH-II > Buserelin > sGnRH > catfish (cf) GnRH > human (m) GnRH. Though Buserelin showed better binding affinity compared to sGnRH, induced breeding experiments with magur showed similar performance of the ligands at the equivalent dose of 20 μg/kg B.W., but the spontaneous release of milt from the males was not observed in both cases. Significantly better reproductive parameters were recorded with Buserelin at the dose of 30 μg/kg B.W.

Conclusion:

The study revealed that that the GnRHa Buserelin can be used as an effective inducing agent for breeding in C. magur.