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Gene expression during endochondral bone development: Evidence for coordinate expression of transforming growth factor β 1 and collagen type I
Author(s) -
Bortell Rita,
Barone Leesa M.,
Tassinari Melissa S.,
Lian Jane B.,
Stein Gary S.
Publication year - 1990
Publication title -
journal of cellular biochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.028
H-Index - 165
eISSN - 1097-4644
pISSN - 0730-2312
DOI - 10.1002/jcb.240440203
Subject(s) - endochondral ossification , cartilage , messenger rna , microbiology and biotechnology , biology , stromal cell , gene expression , osteoblast , type i collagen , bone cell , chemistry , endocrinology , medicine , gene , anatomy , in vitro , genetics , cancer research
Subcutaneous implatation of demineralized bone particles (DBP) into rats induces the formation of a bone ossicle by a tightly controlled sequence of chondro‐ and osteo‐inductive events which are directly comparable to those which occur in normal endochondral bone development. Although the morphological and biochemical sequence associated with endochondral bone formation in this model has been well characterized, to date little information is available as to the gene regulation by which these events occur. To examine the expression of genes in this system, RNA was isolated from implants every 2 days over a time course spanning 3 to 19 days after implantation of DBP into rats. Cellular levels of mRNA transcripts of cell‐growth‐regulated and tissue‐specific genes were examined by slot blot analysis and compared to the morphological changes occuring during formation of the ossicle. Analysis of the mRNA levels of histone H4 and c‐myc, markers of proliferative activity, revealed several periods of actively proliferating cells, corresponding to (1) production of fibroprogenitor cells (day 3), (2) onset of bone formation (day 9), and (3) formation of bone marrow (day 19). The mRNA levels of collagen type II, a phenotypic marker of cartilage, peaked between days 7 and 9 post‐implantation, corresponding to the appearance of chondrocytes in the implant, and rapidly declined on day 11 (to 5% of maximum value) when bone formation was observed. The peak mRNA levels of collagen type I, found in fibroblasts and osteoblasts, occurred first with the onset of bone formation (days 7–10) and again during formation of bone marrow (day 19). This study has demonstrated that the temporal patterns of mRNA expression of cartilage type II and bone type I collagens coincide with the morphological sequence in this model of endochondral bone formation. Further, the mRNA levels of transforming growth factor β 1 (TGFβ) were compared to those of collagen types I and II; a direct temporal correlation of TGFβ mRNA levels with that of collagen type I was found throughout the developmental time course. This observation of a tightly coupled relationship between TGFβ and type I collagen mRNA levels is consistent with a functional role for TGFβ in extracellular matrix production during in vivo bone formation.