Gradients in bone morphogenetic protein-related gene expression across the growth plate.
In the growth plate, stem-like cells in the resting zone differentiate into rapidly dividing chondrocytes of the proliferative zone and then terminally differentiate into the non-dividing chondrocytes of the hypertrophic zone. To explore the molecular switches responsible for this two-step differentiation program, we developed a microdissection method to isolate RNA from the resting (RZ), proliferative (PZ), and hypertrophic zones (HZ) of 7-day-old male rats. Expression of approximately 29,000 genes was analyzed by microarray and selected genes verified by real-time PCR. The analysis identified genes whose expression changed dramatically during the differentiation program, including multiple genes functionally related to bone morphogenetic proteins (BMPs). BMP-2 and BMP-6 were upregulated in HZ compared with RZ and PZ (30-fold each, P < 0.01 and 0.001 respectively). In contrast, BMP signaling inhibitors were expressed early in the differentiation pathway; BMP-3 and gremlin were differentially expressed in RZ (100- and 80-fold, compared with PZ, P < 0.001 and 0.005 respectively) and growth differentiation factor (GDF)-10 in PZ (160-fold compared with HZ, P < 0.001). Our findings suggest a BMP signaling gradient across the growth plate, which is established by differential expression of multiple BMPs and BMP inhibitors in specific zones. Since BMPs can stimulate both proliferation and hypertrophic differentiation of growth plate chondrocytes, these findings suggest that low levels of BMP signaling in the resting zone may help maintain these cells in a quiescent state. In the lower RZ, greater BMP signaling may help induce differentiation to proliferative chondrocytes. Farther down the growth plate, even greater BMP signaling may help induce hypertrophic differentiation. Thus, BMP signaling gradients may be a key mechanism responsible for spatial regulation of chondrocyte proliferation and differentiation in growth plate cartilage.
Nilsson
Ola
O
Developmental Endocrinology Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA. ola.nilsson@ki.se
Parker
Elizabeth A
EA
Hegde
Anita
A
Chau
Michael
M
Barnes
Kevin M
KM
Baron
Jeffrey
J
D000818:Animals; D055396:Bone Morphogenetic Protein 2; D055398:Bone Morphogenetic Protein 3; D055418:Bone Morphogenetic Protein 6; D055419:Bone Morphogenetic Protein 7; D019485:Bone Morphogenetic Proteins / Q000235:genetics*; D019902:Chondrocytes / Q000166:cytology* / Q000378:metabolism; D016207:Cytokines; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental; D006023:Glycoproteins / Q000235:genetics; D055413:Growth Differentiation Factor 10; D006132:Growth Plate / Q000378:metabolism*; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics; D008297:Male; D020411:Oligonucleotide Array Sequence Analysis; D011506:Proteins; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016212:Transforming Growth Factor beta / Q000235:genetics
C525720:Bmp2 protein, rat; C525759:Bmp3 protein, rat; C525818:Bmp6 protein, rat; C525821:Bmp7 protein, rat; D055396:Bone Morphogenetic Protein 2; D055398:Bone Morphogenetic Protein 3; D055418:Bone Morphogenetic Protein 6; D055419:Bone Morphogenetic Protein 7; D019485:Bone Morphogenetic Proteins; D016207:Cytokines; C525786:Gdf10 protein, rat; D006023:Glycoproteins; C107276:Grem1 protein, rat; D055413:Growth Differentiation Factor 10; D036341:Intercellular Signaling Peptides and Proteins; D011506:Proteins; D012333:RNA, Messenger; D016212:Transforming Growth Factor beta; C054234:chordin