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Latent transforming growth factor‐β is present in the extracellular matrix of embryonic hearts in situ
Author(s) -
Ghosh Subhadra,
Brauer Philip R.
Publication year - 1996
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/(sici)1097-0177(199602)205:2<126::aid-aja4>3.0.co;2-k
Subject(s) - immunostaining , biology , transforming growth factor , extracellular matrix , embryonic heart , microbiology and biotechnology , embryonic stem cell , immunology , biochemistry , immunohistochemistry , gene
Transforming growth factor‐β (TGF‐β) is an important regulator of development.In vitro, TGF‐β is secreted in a latent, inactive form and can be activated by pH extremes,chaotropic agents, or cell‐surface proteases. However, there is little evidence for the existence oflatent TGF‐β in vivo. In this study, we determined whether (1) cultured embryonic cardiacsegments secrete latent or active TGF‐β, (2) binding of TGF‐β antibody to TGF‐βwas conformation‐dependent (i.e., active vs. latent), and (3) immunostaining of embryonic heartschanged after exposure to activating conditions. Only latent TGF‐β3 (acid activatable) wasdetected in conditioned medium of stage 14–16 chick cardiac segments as measured bya growth inhibition bioassay. No growth‐inhibitory activity was present in nonacidified controlmedium. When blotted onto a membrane, only transiently acidified conditioned medium boundTGF‐β antibody. These data showed that cardiac segments secrete latent TGF‐β whichbinds with antibody if activated. To determine if antibody binding to tissue sections requiredexposure to TGF‐β‐activating conditions, stage 14–16 embryos were fixed andsectioned under conditions that maximally retained extracellular matrix (ECM). Under theseconditions, immunostaining was found in the myocardium but not in the endocardium or cardiacECM. Limited immunostaining was found in other areas of the embryo and was alwayscell‐associated. In addition to the above staining, when tissue sections were exposed toTGF‐β activating conditions, immunopositive staining was present within most of theembryonic ECM including the cardiac ECM. All immunostaining was blocked by preabsorptionwith TGF‐β3 protein. These data suggest that active TGF‐β has a very limiteddistribution while latent TGF‐β is more abundant in embryonic ECM. Therefore, in vivoactivation of TGF‐β may play an important role in mediating the expression of TGF‐βfunction during development. © 1996 Wiley‐Liss, Inc.