Transforming growth factor‐β in the early mouse embryo: Implications for the regulation of muscle formation and implantation

Abstract

In a search for functions of transforming growth factor-beta during early embryonic development we used two different experimental approaches. In the first we made use of embryonic stem (ES) cells. ES cells in culture differentiate to derivatives of all three germ layers and mimic some aspects of organogenesis when grown as aggregates in suspension to form embryoid bodies. Differentiation proceeds further when the embryoid bodies attach to suitable substrates. Muscle and neuronal cells are among the most readily identified cell types then formed. We examined the effect of all-trans retinoic acid (RA) and members of the transforming growth factor-beta family (TGF-beta 1, TGF-beta 2) under these conditions in an assay where single aggregates formed in hanging microdrops in medium supplemented with serum depleted of lipophilic substances which would include retinoids. Endoderm-like cells formed under all conditions tested. RA at concentrations of 10(-8) M and 10(-7) M induced the formation of neurons but in the absence of RA or at concentrations up to 10(-9) M, neurons were not observed. Instead, beating muscle formed in about one-third of the plated aggregates; this was greatly reduced when RA concentrations increased above 10(-9) M. Immunofluorescent staining for muscle specific myosin showed that two muscle cell types could be distinguished: elongated, non-contractile myoblasts and mononucleate flat cells. The mononucleate flat cells appeared to correspond with rhythmically contracting muscle. The number of non-contractile myoblasts increased 3-fold over controls in the presence of 10(-9) M RA. TGF-beta s increased the number of contractile and non-contractile muscle cells by a factor 3 to 7 over controls, depending on the TGF-beta isoform added and the muscle cell type formed. TGF-beta 2 also invariably increased the rate at which contracting muscle cells were first observed in replated aggregates. The stimulatory effect of TGF-beta s on the formation of mononucleate flat cells was completely abrogated by RA at 10(-9) M while the number of myoblasts under similar conditions was unchanged. These data suggest that a complex interplay between retinoids and TGF-beta isoforms may be involved in regulation of differentiation in early myogenesis. In the second approach, neutralizing polyclonal rabbit antibodies specific for TGF-beta 2 were injected into the cavity of mouse blastocysts 3.5 days post coîtum (pc). After 1 day in culture, embryos were transferred to pseudopregnant females. The number of decidua, embryos and resorptions were counted at day 8.5-9.5 pc.(ABSTRACT TRUNCATED AT 400 WORDS)

Fluid Shear Stress Regulates the Expression of TGF-β1 and Its Signaling Molecules in Mouse Embryo Mesenchymal Progenitor Cells

“…TGF-β1 is well known to induce differentiation of mesenchymal cells toward a SMC phenotype. The addition of TGF-β1 generally inhibits myoblast differentiation [8], but stimulates differentiation of embryonic myoblasts [9]. TGF-β1 was reported to block myogenic differentiation through inhibition of type II TGF-β1 receptor signaling in C2C12 myoblasts [10].…”

Differentiation of embryonic stem cells into hepatocytes: Biological functions and therapeutic application

“…E mbryonic stem (ES) cells were first identified in the mouse system and are capable of differentiating in vitro into multiple cell types. 1 In the past decade, several growth factors and transcription factors have been shown capable of directing differentiation of mouse ES cells into multicell lineage in vitro, e.g., retinoic acid induces neurons, 2 cytokines induce hematopoietic cells, 3,4 fibroblast growth factors induce hematopoietic cells, 5 transforming growth factor induces myogenesis, 6 and hepatic nuclear factor (HNF)-3 induces endoderm cells. ES cells cultured on several different feeder cell layers are also able to differentiate into specific cell types.…”

Activities of growth factors in preimplantation embryos

“…Rappolee et al Rizzino and Bowen-Pope, 1985Palmieri et al, 1992aParia and Dey, 1990Slager et al, 1993Tartakovsky and Ben-Yair, 1991Tartakovsky and Ben-Yair, 1991 is known that the membrane proteins of the apical surface of an epithelial layer become less laterally mobile after the formation of tight junctions. The EGF-receptors could contribute to the polarization of the outer blastomeres by their inability to move to all cell surfaces after the formation of tight junctions.…”