Cloning, characterization, and spatio-temporal expression patterns of HdhSPARC and its responses to multiple stressors

SPARC is an extracellular Ca2+-binding, secreted glycoprotein that plays a dynamic role in the growth and development of organisms. This study aimed to describe the isolation, characterization, and expression analysis of HdhSPARC in Pacific abalone (Haliotis discus hannai) to infer its potential functional role. The isolated HdhSPARC was 1633 bp long, encoding a polypeptide of 284 amino acid residues. Structurally, the SPARC protein in abalone is comprised of three biological domains. However, the structure of this protein varied between vertebrates and invertebrates, as suggested by their distinct clustering patterns in phylogenetic analysis. In early development, HdhSPARC was variably expressed, and higher expression was found in veliger larvae. Moreover, HdhSPARC was highly expressed in juvenile abalone with rapid growth compared to their slower-growing counterparts. Among the testicular development stages, the growth stage exhibited higher HdhSPARC expression. HdhSPARC was also upregulated during muscle remodeling and shell biomineralization, as well as in response to different stressors such as heat shock, LPS, and H2O2 exposure. However, this gene was downregulated in Cd-exposed abalone. The present study first comprehensively characterized the HdhSPARC gene, and its spatio-temporal expressions were analyzed along with its responses to various stressors.

The BMP signaling gradient is interpreted through concentration thresholds in dorsal-ventral axial patterning

Bone Morphogenetic Protein (BMP) patterns the dorsal–ventral (DV) embryonic axis in all vertebrates, but it is unknown how cells along the DV axis interpret and translate the gradient of BMP signaling into differential gene activation that will give rise to distinct cell fates. To determine the mechanism of BMP morphogen interpretation in the zebrafish gastrula, we identified 57 genes that are directly activated by BMP signaling. By using Seurat analysis of single-cell RNA sequencing (scRNA-seq) data, we found that these genes are expressed in at least 3 distinct DV domains of the embryo. We distinguished between 3 models of BMP signal interpretation in which cells activate distinct gene expression through interpretation of thresholds of (1) the BMP signaling gradient slope; (2) the BMP signal duration; or (3) the level of BMP signal activation. We tested these 3 models using quantitative measurements of phosphorylated Smad5 (pSmad5) and by examining the spatial relationship between BMP signaling and activation of different target genes at single-cell resolution across the embryo. We found that BMP signaling gradient slope or BMP exposure duration did not account for the differential target gene expression domains. Instead, we show that cells respond to 3 distinct levels of BMP signaling activity to activate and position target gene expression. Together, we demonstrate that distinct pSmad5 threshold levels activate spatially distinct target genes to pattern the DV axis.

This study tested three models of how a BMP morphogen gradient is translated into differential gene activation that specifies distinct cell fates, finding that BMP signal concentration thresholds, not gradient shape or signal duration, position three distinct gene activation domains.

Ziyuglycoside II alleviates cyclophosphamide-induced leukopenia in mice via regulation of HSPC proliferation and differentiation

Ziyuglycoside II (ZGS II) is a major bioactive ingredient of Sanguisorbae officinalis L., which has been widely used for managing myelosuppression or leukopenia induced by chemotherapy or radiotherapy. In the current study, we investigated the pro-hematopoietic effects and underlying mechanisms of ZGS II in cyclophosphamide-induced leukopenia in mice. The results showed that ZGS II significantly increased the number of total white blood cells and neutrophils in the peripheral blood. Flow cytometry analysis also showed a significant increase in the number of nucleated cells and hematopoietic stem and progenitor cells (HSPCs) including ST-HSCs, MPPs, and GMPs, and enhanced HSPC proliferation in ZGS II treated mice. The RNA-sequencing analysis demonstrated that ZGS II effectively regulated cell differentiation, immune system processes, and hematopoietic system-related pathways related to extracellular matrix (ECM)-receptor interaction, focal adhesion, hematopoietic cell lineage, cytokine-cytokine receptor interaction, the NOD-like receptor signaling pathway, and the osteoclast differentiation pathway. Moreover, ZGS II treatment altered the differentially expressed genes (DEGs) with known functions in HSPC differentiation and mobilization (Cxcl12, Col1a2, and Sparc) and the surface markers of neutrophilic precursors or neutrophils (Ngp and CD177). Collectively, these data suggest that ZGS II protected against chemotherapy-induced leukopenia by regulating HSPC proliferation and differentiation.

Matricellular Proteins: Functional Insights From Non-mammalian Animal Models

The extracellular matrix (ECM) has central roles in tissue integrity and remodeling throughout the life span of animals. While collagens are the most abundant structural components of ECM in most tissues, tissue-specific molecular complexity is contributed by ECM glycoproteins. The matricellular glycoproteins are categorized primarily according to functional criteria and represented predominantly by the thrombospondin, tenascin, SPARC/osteonectin, and CCN families. These proteins do not self-assemble into ECM fibrils; nevertheless, they shape ECM properties through interactions with structural ECM proteins, growth factors, and cells. Matricellular proteins also promote cell migration or morphological changes through adhesion-modulating or counter-adhesive actions on cell-ECM adhesions, intracellular signaling, and the actin cytoskeleton. Typically, matricellular proteins are most highly expressed during embryonic development. In adult tissues, expression is more limited unless activated by cues for dynamic tissue remodeling and cell motility, such as occur during inflammatory response and wound repair. Many insights in the complex roles of matricellular proteins have been obtained from studies of gene knockout mice. However, with the exception of chordate-specific tenascins, these are highly conserved proteins that are encoded in many animal phyla. This review will consider the increasing body of research on matricellular proteins in nonmammalian animal models. These models provide better access to the very earliest stages of embryonic development and opportunities to study biological processes such as limb and organ regeneration. In aggregate, this research is expanding concepts of the functions and mechanisms of action of matricellular proteins.

Molecular cloning and characterization of the matricellular protein Sparc/osteonectin in flatfish, Scophthalmus maximus, and its developmental stage-dependent transcriptional regulation during metamorphosis

SPARC/osteonectin is a multifunctional matricellular glycoprotein, which is expressed in embryonic and adult tissues that undergo active proliferation and dynamic morphogenesis. Recent studies indicate that Sparc expression appears early in development, although its function and regulation during development are largely unknown. In this report, we describe the isolation, characterization, post-embryonic developmental expression and environmental thermal regulation of sparc in turbot. The full-length turbot sparc cDNA contains 930 bp and encodes a protein of 310 amino acids, which shares 77, 75 and 80% identity with human, frog and zebrafish, respectively. Results of whole-mount in situ hybridization reveal a dynamic expression profile during post-embryonic turbot development. Sparc is expressed differentially in the cranioencephalic region; mainly in jaws, branchial arches, fin folds and rays of caudal, dorsal and anal fins. Furthermore, ontogenetic studies demonstrated that Sparc gene expression is dynamically regulated during post-embryonic turbot development, with high expression during stage-specific post-embryonic remodeling. Additionally, the effect of thermal environmental conditions on turbot development and on ontogenetic sparc expression was evaluated.

Matricellular protein SPARC/osteonectin expression is regulated by DNA methylation in its core promoter region

BACKGROUND

SPARC/osteonectin is an evolutionarily conserved matricellular protein that modulates cell-matrix interaction and cell function. In all vertebrates, SPARC is dynamically expressed during embryogenesis. However, the precise function of SPARC and the regulatory elements required for its expression in particular during early embryogenesis are largely unknown.

RESULTS

The present study was undertaken to explore the molecular mechanisms that regulate sparc gene expression by in vivo functional characterization of the sparc promoter and identification of possible putative regulatory elements that govern basal promoter activity. We report here transient expression analyses of eGFP expression from transgenic zebrafish containing a Sparc-iTol2-eGFP-BAC and/or 7.25 kb-sparc-Tol2-eGFP constructs. eGFP expression was specifically found in the notochord, otic vesicle, fin fold, intermediate cell mass, and olfactory placode of BAC and Tol2 transposon vectors injected embryos. Deletion analysis revealed that promoter activity resides in the unique 5'-untranslated intronic region. Computer-based analysis revealed a putative CpG island immediately proximal to the translation start site within the intron sequence. Global inhibition of methylation with 5-Aza-2-deoxycytidine promoted sparc expression in association with decreasing CpG methylation.

CONCLUSIONS

Taken together, these data identify a contributory role for DNA methylation in regulating sparc expression in zebrafish embryogenesis.