Identification of a new cartilage-specific S100-like protein up-regulated during endo/perichondral mineralization in gilthead seabream

Exploring Immunohistochemistry in Fish: Assessment of Antibody Reactivity by Western Immunoblotting

In recent years, research on fish has seen remarkable advancements, especially in aquaculture, ornamental fish industry, and biomedical studies. Immunohistochemistry has become crucial in fish research, aiding in physiological and pathological investigations. However, the use of antibodies originally developed for mammals has raised concerns about their cross-reactivity and specificity in fish. This study systematically evaluated the reactivity of commonly used antibodies for diagnostic purposes, especially in fish pathology, including pan-cytokeratin, vimentin, S-100, glial fibrillary acidic protein, and desmin in the tissue of Sparus aurata, Dicentrarchus labrax, Oncorhynchus mykiss, and Carassius auratus. Western immunoblotting was employed to assess antibody specificity. The results revealed that the pan-cytokeratin and glial fibrillary acidic protein antibodies cross-react with all tested fish species, while S-100 demonstrated specific staining in sea bream, goldfish, and rainbow trout tissues. Conversely, vimentin and desmin antibodies displayed no reactivity. In conclusion, the anti-cytokeratin clone AE1/AE3 and the polyclonal rabbit anti-glial fibrillary acidic protein antibody, which are extensively used in mammals, were validated for fish immunohistochemical studies. Regrettably, D33 anti-desmin and V9 anti-vimentin clones are unsuitable for immunohistochemistry in the tested fish. These findings underscore the need for species-specific antibodies and proper validation for accurate immunohistochemistry analyses in fish research.

Immunohistochemical investigation of epithelial, mesenchymal, neuroectodermal, immune and endocrine markers in sterlet (Acipenser ruthenus), shortnose sturgeon (Acipenser brevirostrum) and common carp (Cyprinus carpio)

Immunohistochemistry (IHC) is a laboratory method widely used to characterize tissue and cell origin, both in human and veterinary medicine. In fish, however, little is known about staining characteristics of most tissue types, and especially for less studied chondrostean fish. The aim of this study was to examine the specificity of various immunohistochemical markers in tissues of chondrostean and teleostean fish and to validate diagnostic tests. Sterlet (Acipenser ruthenus L.), shortnose sturgeon (Acipenser brevirostrum) and common carp (Cyprinus carpio L.) were examined. Markers were chosen as representatives of epithelial (cytokeratin AE1/AE3), mesenchymal (vimentin), neuroectodermal (S-100 protein), lymphoid (leukocyte common antigen, LCA) and endocrine (thyroglobulin, thyroxin) tissues and organs. Applied antibodies were of monoclonal or polyclonal mammalian origin and primarily intended for human medicine research or diagnostic application. No species differences were obvious while examining sterlet, shortnose sturgeon and carp. Cytokeratin AE1/AE3, vimentin, S-100 protein and thyroxin were positive on targeted tissues and structures. Leukocyte common antigen (LCA) and thyroglobulin were negative on targeted structures, however, and with clear cross-reactivity on non-targeted tissues (vascular wall, granulocytes). Conclusive results were obtained when using polyclonal antibodies with dilution adjusted to laboratory practice, while application of ready-to-use (RTU) kits with pre-diluted antibodies or monoclonal antibodies often showed conflicting or inconclusive results.

Rodlet cells in kidney of goldfish (Carassius auratus, Linnaeus 1758): A light and confocal microscopy study

Rodlet cells (RCs) have always been an enigma for scientists. RCs have been given a variety of activities over the years, including ion transport, osmoregulation, and sensory function. These cells, presumably as members of the granulocyte line, are present only in teleosts and play a role in the innate immune response. RCs are migratory cells found in a variety of organs, including skin, vascular, digestive, uropoietic, reproductive, and respiratory systems, and present distinct physical properties that make them easily recognizable in tissues and organs. The development of RCs can be divided into four stages: granular, transitional, mature, and ruptured, having different morphological characteristics. Our study aims to characterize the different stages of these cells by histomorphological and histochemical techniques. Furthermore, we characterized these cells at all stages with peroxidase and fluorescence immunohistochemical techniques using different antibodies: S100, tubulin, α-SMA, piscidin, and for the first time TLR-2. From our results, the immunoreactivity of these cells to the antibodies performed may confirm that RCs play a role in fish defense mechanisms, helping to expand the state of the art on immunology and immune cells of teleosts.

Marking vertebrates langerhans cells, from fish to mammals

Langerhans cells (LCs) are specialized dendritic cells (DCs) that play a defense role in recognizing foreign antigens, in tissue where antigenic exposures occur, as in the skin and mucous membranes. LCs are able to continuously move within the tissues thanks to dendritic contraction and distension performing their surveillance and/or phagocytosis role. These cells are characterized by the presence of Birbeck granules in their cytoplasm, involved in endocytosis. LCs have been characterized in several classes of vertebrates, from fish to mammals using different histological and molecular techniques. The aim of the present review is to define the state of art and the need of information about immunohistochemical markers of LCs in different classes of vertebrates. The most used immunohistochemical (IHC) markers are Langerin/CD207, CD1a, S-100 and TLR. These IHC markers are described in relation to their finding in different vertebrate classes with phylogenetical considerations. Among the four markers, Langerin/CD207 and TLR have the widest spectrum of cross reactivity in LCs.

Cells Isolated from Regenerating Caudal Fin of Sparus aurata Can Differentiate into Distinct Bone Cell Lineages

Teleosts have the ability to regenerate their caudal fin upon amputation. A highly proliferative mass of undifferentiated cells called blastema forms beneath wound epidermis and differentiates to regenerate all missing parts of the fin. To date, the origin and fate of the blastema is not completely understood. However, current hypotheses suggest that the blastema is comprised of lineage-restricted dedifferentiated cells. To investigate the differentiation capacity of regenerating fin-derived cells, primary cultures were initiated from the explants of 2-days post-amputation (dpa) regenerates of juvenile gilthead seabream (Sparus aurata). These cells were subcultured for over 30 passages and were named as BSa2. After 10 passages they were characterized for their ability to differentiate towards different bone cell lineages and mineralize their extracellular matrix, through immunocytochemistry, histology, and RT-PCR. Exogenous DNA was efficiently delivered into these cells by nucleofection. Assessment of lineage-specific markers revealed that BSa2 cells were capable of osteo/chondroblastic differentiation. BSa2 cells were also found to be capable of osteoclastic differentiation, as demonstrated through TRAP-specific staining and pit resorption assay. Here, we describe the development of the first successful cell line viz., BSa2, from S. aurata 2-dpa regenerating caudal fins, which has the ability of multilineage differentiation and is capable of in vitro mineralization. The availability of such in vitro cell systems has the potential to stimulate research on the mechanisms of cell differentiation during fin regeneration and provide new insights into the mechanisms of bone formation.

Development of Teleost Intermuscular Bones Undergoing Intramembranous Ossification Based on Histological-Transcriptomic-Proteomic Data

Intermuscular bones (IBs) specially exist in lower teleost fish and the molecular mechanism for its development remains to be clarified. In this study, different staining methods and comparative proteomics were conducted to investigate the histological structure and proteome of IB development in Megalobrama amblycephala, including four key IB developmental stages (S1-IBs have not emerged in the tail part; S2-several small IBs started to ossify in the tail part; S3-IBs appeared rapidly; S4-all the IBs appeared with mature morphology). Alcian blue and alizarin red S stained results indicated that IBs were gradually formed from S2 to S4, undergoing intramembranous ossification without a cartilaginous phase. A total of 3368 proteins were identified by using the isobaric tags for relative and absolute quantitation (iTRAQ) approach. Functional annotation showed that proteins which were differentially expressed among stages were involved in calcium, MAPK, Wnt, TGF-β, and osteoclast pathways which played a critical role in bone formation and differentiation. Three proteins (collagen9α1, stat1, tnc) associated with chondrocytes did not exhibit significant changes through S2 to S4; however, proteins (entpd5, casq1a, pvalb, anxa2a, anxa5) which associated with osteoblasts and bone formation and differentiation showed significantly a higher expression level from S1 to S2, as well as to S3 and S4. These further demonstrated that development of IBs did not go through a cartilaginous phase. The inhibitors of TGF-β and Wnt pathways were tested on zebrafish (sp7/eGFP) and the results indicated that both inhibitors significantly delayed IB development. This study provides a comprehensive understanding of the IB ossification pattern, which will help further elucidate the molecular mechanisms for IB development in teleosts.

Identification of a fish short-chain dehydrogenase/reductase associated with bone metabolism

Although human and mouse genetics have largely contributed to the better understanding of the mechanisms underlying skeletogenesis, much more remains to be uncovered. In this regard alternative and complementary systems have been sought and cell systems capable of in vitro calcification have been developed to study the mechanisms underlying bone formation. In gilthead seabream (Sparus aurata), a gene coding for an unknown protein that is strongly up-regulated during extracellular matrix (ECM) mineralization of a pre-osteoblast cell line was recently identified as a potentially important player in bone formation. In silico analysis of the deduced protein revealed the presence of domains typical of short-chain dehydrogenase/reductases (SDR). Closely related to carbonyl reductase 1, seabream protein belongs to a novel subfamily of SDR proteins with no orthologs in mammals. Analysis of gene expression by qPCR confirmed the strong up-regulation of sdr-like expression during in vitro mineralization but also revealed high expression levels in calcified tissues. A possible role for Sdr-like in osteoblast and bone metabolism was further evidenced through (i) the localization by in situ hybridization of sdr-like transcript in pre-osteoblasts of the operculum and (ii) the regulation of sdr-like gene transcription by Runx2 and retinoic acid receptor, two regulators of osteoblast differentiation and mineralization. Expression data also indicated a role for Sdr-like in gastrointestinal tract homeostasis and during gilthead seabream development at gastrulation and metamorphosis. This study reports a new subfamily of short-chain dehydrogenases/reductases in vertebrates and, for the first time, provides evidence of a role for SDRs in bone metabolism, osteoblast differentiation and/or tissue mineralization.

Central role of betaine-homocysteine S-methyltransferase 3 in chondral ossification and evidence for sub-functionalization in neoteleost fish

BACKGROUND

To better understand the complex mechanisms of bone formation it is fundamental that genes central to signaling/regulatory pathways and matrix formation are identified. Cell systems were used to analyze genes differentially expressed during extracellular matrix mineralization and bhmt3, coding for a betaine-homocysteine S-methyltransferase, was shown to be down-regulated in mineralizing gilthead seabream cells.

METHODS

Levels and sites of bhmt3 expression were determined by qPCR and in situ hybridization throughout seabream development and in adult tissues. Transcriptional regulation of bhmt3 was assessed from the activity of promoter constructs controlling luciferase gene expression. Molecular phylogeny of vertebrate BHMT was determined from maximum likelihood analysis of available sequences.

RESULTS

bhmt3 transcript is abundant in calcified tissues and localized in cartilaginous structures undergoing endo/perichondral ossification. Promoter activity is regulated by transcription factors involved in bone and cartilage development, further demonstrating the central role of Bhmt3 in chondrogenesis and/or osteogenesis. Molecular phylogeny revealed the explosive diversity of bhmt genes in neoteleost fish, while tissue distribution of bhmt genes in seabream suggested that neoteleostean Bhmt may have undergone several steps of sub-functionalization.

CONCLUSIONS

Data on bhmt3 gene expression and promoter activity evidences a novel function for betaine-homocysteine S-methyltransferase in bone and cartilage development, while phylogenetic analysis provides new insights into the evolution of vertebrate BHMTs and suggests that multiple gene duplication events occurred in neoteleost fish lineage.

GENERAL SIGNIFICANCE

High and specific expression of Bhmt3 in gilthead seabream calcified tissues suggests that bone-specific betaine-homocysteine S-methyltransferases could represent a suitable marker of chondral ossification.

Transcriptional regulation of gilthead seabream bone morphogenetic protein (BMP) 2 gene by bone- and cartilage-related transcription factors

Bone morphogenetic protein (BMP) 2 belongs to the transforming growth factor β (TGFβ) superfamily of cytokines and growth factors. While it plays important roles in embryo morphogenesis and organogenesis, BMP2 is also critical to bone and cartilage formation. Protein structure and function have been remarkably conserved throughout evolution and BMP2 transcription has been proposed to be tightly regulated, although few data is available. In this work we report the cloning and functional analysis of gilthead seabream BMP2 promoter. As in other vertebrates, seabream BMP2 gene has a 5′ non-coding exon, a feature already present in DPP gene, the fruit fly ortholog of vertebrate BMP2 gene, and maintained throughout evolution. In silico analysis of seabream BMP2 promoter revealed several binding sites for bone and cartilage related transcription factors (TFs) and their functionality was evaluated using promoter-luciferase constructions and TF-expressing vectors. Runt-related transcription factor 3 (RUNX3) was shown to negatively regulate BMP2 transcription and combination with the core binding factor β (CBFβ) further reduced transcriptional activity of the promoter. Although to a lesser extent, myocyte enhancer factor 2C (MEF2C) had also a negative effect on the regulation of BMP2 gene transcription, when associated with SRY (sex determining region Y)-box 9 (SOX9b). Finally, v-ets avian erythroblastosis virus E26 oncogene homolog 1 (ETS1) was able to slightly enhance BMP2 transcription. Data reported here provides new insights toward the better understanding of the transcriptional regulation of BMP2 gene in a bone and cartilage context.

Mechanisms of morphogenetic disorders in the lower jaw under the influence of heavy metal salts on the body

In the experiment on the 36 mature rats, the peculiarities of morphological disorders in the lower jaw of rats under the influence of salts of chromium, lead, zinc, iron, copper, and manganese are showed. Profound morphological changes in bone and cartilaginous tissues of lower jaw are followed by disorders of bone mineral content. The importance of the S100 protein in morphological changes in bone and cartilaginous tissues under the influence of heavy metal salts is shown.

Comparative analysis of a teleost skeleton transcriptome provides insight into its regulation

An articulated endoskeleton that is calcified is a unifying innovation of the vertebrates, however the molecular basis of the structural divergence between terrestrial and aquatic vertebrates, such as teleost fish, has not been determined. In the present study long-read next generation sequencing (NGS, Roche 454 platform) was used to characterize acellular perichondral bone (vertebrae) and chondroid bone (gill arch) in the gilthead sea bream (Sparus auratus). A total of 15.97 and 14.53Mb were produced, respectively from vertebrae and gill arch cDNA libraries and yielded 32,374 and 28,371 contigs (consensus sequences) respectively. 10,455 contigs from vertebrae and 10,625 contigs from gill arches were annotated with gene ontology terms. Comparative analysis of the global transcriptome revealed 4249 unique transcripts in vertebrae, 4201 unique transcripts in the gill arches and 3700 common transcripts. Several core gene networks were conserved between the gilthead sea bream and mammalian skeleton. Transcripts for putative endocrine factors were identified in acellular gilthead sea bream bone suggesting that in common with mammalian bone it can act as an endocrine tissue. The acellular bone of the vertebra, in contrast to current opinion based on histological analysis, was responsive to a short fast and significant (p<0.05) down-regulation of several transcripts identified by NGS, osteonectin, osteocalcin, cathepsin K and IGFI occurred. In gill arches fasting caused a significant (p<0.05) down-regulation of osteocalcin and up-regulation of MMP9.

Evolution of the S100 family of calcium sensor proteins

The S100s are a large group of Ca(2+) sensors found exclusively in vertebrates. Transcriptomic and genomic data from the major radiations of mammals were used to derive the evolution of the mammalian S100s genes. In human and mouse, S100s and S100 fused-type proteins are in a separate clade from other Ca(2+) sensor proteins, indicating that an ancient bifurcation between these two gene lineages has occurred. Furthermore, the five genomic loci containing S100 genes have remained largely intact during the past 165 million years since the shared ancestor of egg-laying and placental mammals. Nonetheless, interesting births and deaths of S100 genes have occurred during mammalian evolution. The S100A7 loci exhibited the most plasticity and phylogenetic analyses clarified relationships between the S100A7 proteins encoded in the various mammalian genomes. Phylogenetic analyses also identified four conserved subgroups of S100s that predate the rise of warm-blooded vertebrates: A2/A3/A4/A5/A6, A1/A10/A11/B/P/Z, A13/A14/A16, and A7s/A8/A9/A12/G. The similarity between genomic location and phylogenetic clades suggest that these subfamilies arose by a series of tandem gene duplication events. Examination of annotated S100s in lower vertebrates suggests that the ancestral S100 was a member of the A1/A10/A11/B/P/Z subgroup and arose near the emergence of vertebrates approximately 500 million years ago.