Biomedical subjects

H C Slavkin

Publications and source records attributed to H C Slavkin.

At least 55 records · Page 3Linked to original sources

PubMed1999

Convergence of the BMP and EGF signaling pathways on Smad1 in the regulation of chondrogenesis.

Bone morphogenetic protein 4 (BMP4) induces, whereas epidermal growth factor (EGF) inhibits chondrogenesis. We hypothesize that BMP4 and EGF mediated intracellular signals are both coupled in the regulation of Meckel's cartilage development. Two chondrogenic experimental model systems were employed to test the hypothesis: (1) an ex vivo, serum-free, organ culture system for mouse embryonic mandibular processes, and (2) a micromass culture system for chicken embryonic mandibular processes. Chondrogenesis was assayed by alcian blue staining and expression of Sox9 and type II collagen. Exogenous EGF inhibited and BMP4 induced ectopic cartilage in a dose-dependent manner. When BMP4- and EGF-soaked beads were implanted in juxtaposition within embryonic day 10 mouse mandibular processes, the incidence and amount of ectopic cartilage, and Sox9 and type II collagen expression induced by BMP4, were significantly reduced as the concentration of EGF was increased. Similarly, in chicken serum-free micromass cultures, expression of a constitutively active BMP receptor type IB by replication competent avian retrovirus system promoted the rate and extent of chondrogenesis; however, exogenous EGF attenuated this effect. In micromass cultures, BMP signaling resulted in nuclear translocation and accumulation of the signaling molecule Smad1, whereas the addition of EGF inhibited this event. Our results suggest that BMP4 and EGF function antagonistically, yet are coupled in the regulation of initial chondrogenesis. Smad1 serves as a point of convergence for the integration of two different growth factor signaling pathways during chondrogenesis.

Animals↗

PubMed1998

Compressive force promotes sox9, type II collagen and aggrecan and inhibits IL-1beta expression resulting in chondrogenesis in mouse embryonic limb bud mesenchymal cells.

The initial modeling and subsequent development of the skeleton is controlled by complex gene-environment interactions. Biomechanical forces may be one of the major epigenetic factors that determine the form and differentiation of skeletal tissues. In order to test the hypothesis that static compressive forces are transduced into molecular signals during early chondrogenesis, we have developed a unique three-dimensional collagen gel cell culture system which is permissive for the proliferation and differentiation of chondrocytes. Mouse embryonic day 10 (E10) limb buds were microdissected and dissociated into cells which were then cultured within a collagen gel matrix and maintained for up to 10 days. Static compressive forces were exerted onto these cultures. The time course for expression pattern and level for cartilage specific markers, type II collagen and aggrecan, and regulators of chondrogenesis, Sox9 and IL-1beta, were analyzed and compared with non-compressed control cultures. Under compressive conditions, histological evaluation showed an apparent acceleration in the rate and extent of chondrogenesis. Quantitatively, there was a significant 2- to 3-fold increase in type II collagen and aggrecan expression beginning at day 5 of culture and the difference was maintained through 10 days of cultures. Compressive force also causes an elevated level of Sox9, a transcriptional activator of type II collagen. In contrast, the expression and accumulation of IL-1beta, a transcriptional repressor of type II collagen was down-regulated. We conclude that static compressive forces promote chondrogenesis in embryonic limb bud mesenchyme, and propose that the signal transduction from a biomechanical stimuli can be mediated by a combination of positive and negative effectors of cartilage specific extracellular matrix macromolecules.

Aggrecans↗

PubMed1998

Transforming growth factor alpha up-regulates desmin expression during embryonic mouse tongue myogenesis.

Myogenesis is determined by a set of myogenic differentiation factors that are, in turn, regulated by a number of peptide growth factors. During embryonic mouse tongue formation, transforming growth factor alpha (TGF alpha), epidermal growth factor (EGF), and their cognate receptor (EGFR) are co-expressed spatially and temporally with desmin, a muscle-specific structural protein. This investigation tested the hypothesis that TGF alpha directly regulates the myogenic program in developing tongue myoblasts. Mandibular processes from the first branchial arch of embryonic day 10.5 (E10.5) mouse embryos were microdissected and explanted into an organ culture system using serumless chemically defined medium. Exogenous TGF alpha at 10 and 20 ng/ml specifically increased the amount of desmin expression and the number of desmin-positive cells without affecting the general growth and development of the mandibles. This inductive response was detected as early as 2 days after treatment and sustained up to 9 days in culture. EGFR antisense oligonucleotides (30 microM) as well as tyrphostin (80 microM) were able to negate TGF alpha-induced up-regulation of desmin expression. These data indicate that autocrine and/or paracrine action of TGF alpha promotes tongue myogenesis, and that this action is mediated through functional kinase activity of the EGFR. We speculate that the myogenic program in the developing mouse tongue is dependent upon growth factor mediated cell-cell communication of mesenchymal cells originating from the occipital somites and ectomesenchymal cells originating from the cranial neural crest.

Animals↗

PubMed1998

PDGF-A and PDGFR-alpha regulate tooth formation via autocrine mechanism during mandibular morphogenesis in vitro.

Platelet-derived growth factor A (PDGF-A) binding to the PDGF receptor alpha (PDGFR-alpha) mediates signal transduction processes related to DNA synthesis, cell migrations, cytodifferentiation, and wound healing. Recent studies indicate that PDGFR-alpha functions during cranial neural crest cell migrations and first branchial arch morphogenesis (Stephenson et al. [1991] Proc. Natl. Acad. Sci. USA 88:6-10; Morrison-Graham et al. [1992] Development 115:133-142; Hu et al. [1995] Int. J. Dev. Biol. 39:939-945; Soriano [1997] Development 124:2691-2700). The present studies were designed to test the hypothesis that PDGF-A, interacts with its cognate receptor PDGFR-alpha via an autocrine mechanism that regulates the timing, rates, and size of embryonic mouse tooth morphogenesis. Both PDGF-A and PDGFR-alpha transcripts were coordinately expressed in mandibular prominences prior to and during tooth formation using reverse transcriptase-polymerase chain reaction (RT-PCR). During the dental lamina stage, ligand and receptor were present in both enamel organ epithelium and adjacent mesenchymal cells. During the bud stage, ligand and receptor were localized mainly to the enamel organ epithelium. Exogenous PDGF-A at 20 ng/ml enhanced tooth development to reach the cap stage with increased tooth size (P < 0.05) using embryonic day (E)10 mandibular explants cultured in serumless, chemically defined medium. A significant increase in DNA synthesis was observed within enamel organ epithelium at E10+4 when the mandibular explants were treated with PDGF-A at 20 ng/ml. These data suggest that PDGF-A and its cognate receptor (PDGFR-alpha) regulate the size and stage of tooth development via an autocrine mechanism during odontogenesis in vitro.

Animals↗

PubMed1998

Induced expression of myoD, myogenin and desmin during myoblast differentiation in embryonic mouse tongue development.

Significant progress has been made in defining mechanisms governing myogenesis at the transcriptional levels, but the extracellular signal-transduction pathways involved in myogenesis are not as yet defined. The developing mouse tongue provides a model for the regulation of myogenesis during precise time periods in embryogenesis. The molecular cues that regulate the close-range autocrine and/or paracrine signalling processes required for the fast-twitch complex tongue musculature are not known. This study was designed to test the hypothesis that transforming growth factor-alpha (TGF alpha) controls myogenesis in embryonic mouse tongue through the induction of myogenic regulatory factors such as myoD, myf5, myogenin and MRF4/myf6/herculin. To test this hypothesis, the effects of exogenous TGF alpha on the transcription of myoD, myf5, myogenin, MRF4 and desmin were examined in tongue samples from embryonic day-10.5 mandibular explants cultured in serum-free, chemically defined medium and then processed for competitive, reverse transcription-polymerase chain reaction. TGF alpha induced myoD, myogenin and desmin expression. Treatment with 20 and 40 ng/ml TGF alpha decreased or downregulated myf5 mRNA. MRF4 was not detected in the explants. TGF alpha apparently induces the early developmental stages of myogenesis through sequential upregulation of myoD and myogenin, downregulation of myf5 and corresponding significant increases in muscle-specific gene expression such as desmin transcription.

Analysis of Variance↗

PubMed1998

Adenovirus-mediated ectopic expression of Msx2 in even-numbered rhombomeres induces apoptotic elimination of cranial neural crest cells in ovo.

Distinct cranial neural crest-derived cell types (a number of neuronal as well as non-neuronal cell lineages) are generated at characteristic times and positions in the rhombomeres of the hindbrain in developing vertebrate embryos. To examine this developmental process, we developed a novel strategy designed to test the efficacy of gain-of-function Msx2 expression within rhombomeres in ovo prior to the emigration of cranial neural crest cells (CNCC). Previous studies indicate that CNCC from odd-numbered rhombomeres (r3 and r5) undergo apoptosis in response to exogenous BMP4. We provide evidence that targeted infection in ovo using adenovirus containing Msx2 and a reporter molecule indicative of translation can induce apoptosis in either even- or odd-numbered rhombomeres. Furthermore, infected lacZ-control explants indicated that CNCC emigrated, and that 20% of these cells were double positive for crest cell markers HNK-1 and beta-gal. In contrast, there were no HNK-1 and Msx2 double positive cells emigrating from Msx2 infected explants. These results support the hypothesis that apoptotic elimination of CNCC can be induced by 'gain-of-function' Msx2 expression in even-numbered rhombomeres. These inductive interactions involve qualitative, quantitative, positional and temporal differences in TGF-beta-related signals, Msx2 expression and other transcriptional control.

Adenoviridae↗

PubMed1998