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Unique and redundant roles of Smad3 in TGF‐β–mediated regulation of long bone development in organ culture
Author(s) -
Alvarez Jesus,
Serra Rosa
Publication year - 2004
Publication title -
developmental dynamics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.634
H-Index - 141
eISSN - 1097-0177
pISSN - 1058-8388
DOI - 10.1002/dvdy.20100
Subject(s) - biology , transforming growth factor , organ culture , microbiology and biotechnology , transforming growth factor beta , genetics , in vitro
The most well‐characterized intracellular signaling molecules for transforming growth factor‐beta (TGF‐β) are the Smads. R‐Smads interact with and are phosphorylated directly by the TGF‐β type I receptor. Phosphorylated R‐Smads can then associate with Smad4, translocate to the nucleus and regulate transcription. Specific R‐Smads transduce distinct signals for members of the TGF‐β superfamily. Smad2 and ‐3 mediate signaling by TGF‐β/activin, whereas Smad1, ‐5, and ‐8 mediate bone morphogenetic protein signaling. TGF‐β inhibits proliferation and hypertrophic differentiation in metatarsal organ cultures by a perichondrium‐dependent mechanism. To determine the mechanism of TGF‐β signaling in the perichondrium, we tested the hypothesis that TGF‐β–restricted Smad2 and Smad3 regulate chondrocyte proliferation and differentiation in embryonic metatarsal organ cultures. Perichondrium was infected with adenoviruses containing dominant‐negative forms of Smad2 (Ad‐Smad2‐3SA) and Smad3 (Ad‐Smad3ΔC). Proliferation and differentiation were measured in response to treatment with TGF‐β1. Results were compared with control bones infected with a β‐galactosidase reporter virus (Ad‐β‐gal). Infection with Ad‐Smad2‐3SA completely blocked the effects of TGF‐β1 on metatarsal development while Ad‐Smad3ΔC only partially blocked TGF‐β1 effects. To further characterize the role of Smad3 in long bone development, TGF‐β1 responsiveness in cultures from Smad3 +/+ and Smad3 ex8/ex8 mice were compared. Loss of Smad3 only partially blocked the effects of TGF‐β1 on differentiation. In contrast, the effects of TGF‐β1 on chondrocyte proliferation were blocked completely. We conclude that Smad2 signaling in the perichondrium can compensate for the loss of Smad3 to regulate inhibition of hypertrophic differentiation; however, Smad3 is required for TGF‐β1–mediated effects on proliferation. Developmental Dynamics 230:685–699, 2004. © 2004 Wiley‐Liss, Inc.