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In the absence of leukemia inhibitory factor, murine embryonic stem cells cultured in vitro spontaneously aggregate to from three-dimensional embryoid bodies that differentiate to produce hematopoietic, endothelial, muscle, and neuronal cell lineages in a manner recapitulating the events of early embryogenesis. Cardiomyogenesis in embryoid bodies was recently demonstrated to be promoted by PYS-2-derived native SPARC (secreted protein, acidic and rich in cysteine), whose expression is upregulated in parietal endoderm at the onset of the epithelial to mesenchymal transition. Here, we confirm the stimulatory effects of mouse SPARC on cardiomyogenesis using a recombinant baculovirus-produced protein (rmSPARC). Embryoid bodies cultured in the presence of glycosylated rmSPARC, or an unglycosylated peptide spanning the C-terminal EF-hand domain, developed greater numbers of beating cardiomyocytes than did time-matched controls, with enhanced expression of cardiac marker genes including Nkx2.5, Troponin, BMP-2, and MHCα. Histochemical analysis revealed an expansion of the peripheral endoderm, with thicker layers of extracellular matrix (ECM) material observed atop underlying cells. Embryoid bodies treated with SPARC also displayed increased adherence to polystyrene culture dishes, with enhanced expression of ECM mRNAs including collagen IVα3, collagen IVα5, and laminin α1. These results indicate that, in addition to the promotion of cardiomyogenesis, SPARC may also help regulate the molecular composition and organization of ECM secreted by the mesenchymal parietal endoderm. Key words: cardiomyogenesis, SPARC, parietal endoderm, embryoid bodies, epithelial to mesenchymal transition (EMT). Resume : En absence de la chimiokine LIF (<< leukemia inhibitory factor >>), les cellules souches embryonnaires de souris cultivees in vitro s'agregent spontanement pour former des corps embryoides tridimensionnels qui se differencient pour produire des lignees cellulaires hematopoietiques, musculaires et neuronales d'une facon qui recapitule les etapes de l'embryogenese precoce. L'on a demontre recemment que la cardiomyogenese est favorisee par la proteine native SPARC (<< secreted protein, acidic and rich in cysteine >>) produite par les cellules PYS-2, dont l'expression est stimulee lors de la transition epithelium a mesenchyme. Nous confirmons ici les effets stimulateurs de la SPARC de souris sur la cardiomyogenese a l'aide d'une proteine recombinante produite chez le baculovirus (rsSPARC). Les corps embryoides cultives en presence de rsSPARC glycosylee ou d'un peptide non glycosyle qui comprend le domaine EF-hand C-terminal, formaient un plus grand nombre de cardiomyocytes pulsatiles relativement aux controles apparies en fonction du temps. Ceci etait accompagne d'une augmentation de l'expression de marqueurs cardiaques dont les genes Nkx2,5, Troponin, BMP-2 et MHCα. Des analyses histochimiques ont revele une expansion de l'endoderme peripherique et un epaississement de la couche de composantes de la matrice extracellulaire (MEC) observee sur les cellules sous-jacentes. Les corps embryoides traites a la SPARC adheraient davantage au polystyrene des plats de culture et les ARNm des composantes de la MEC, dont le collagene IVα3, le collagene IV α5 et la laminine αl, etaient plus fortement exprimes. Ces resultats indiquent que, en plus de promouvoir la cardiomyogenese, la SPARC peut aussi aider a reguler la composition moleculaire et l'organisation de la MEC secretee par l'endoderme parietal du mesenchyme. [Traduit par la Redaction], Introduction The directed differentiation of embryonic stems cells into cardiomyocytes is emerging as a promising source of cells for cardiac tissue engineering and cell transplantation therapies in the treatment of [...]

Proteins assemble to form frictional complexes is fundamental to efforts in chemistry, structural biology biochemistry, and biophysics. Derived from exons 20, 21, 23, 24, of human elastic, the elastic peptide)(EP) series of proteins are known to coacervate, forming fibrillar aggregates with the high degree of beta-structure and it is believed that overall protein hydropathy and the arrangement of hydropholic domains underpin the self- assembly of these proteins.