Gene expression in the mouse growth plate

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Longitudinal bone growth is a complex process that begins chondrocyte proliferation and subsequent hypertrophy and secretion of extracellular matrix. Subsequently matrix mineralization, vascular invasion, chondrocyte apoptosis, and replacement of chondrocytes by osteocytes lead to the formation of bone. The chondrocytes of the growth plate have been classified into four anatomic zones, reflecting their cellular features and the tissue architecture. In the resting zone (RZ),the ratio of extracellular matrix to cell volume is quite high. The chondrocytes take on a flattened appearance, begin to divide, and organize into columns that extend from proliferating zone (PZ) to maturing zone (MZ). The dividing cells separate from each other and grow larger in the hypertrophic zone (HZ).There are notable biochemical and morphological differences among chondrocytes in each zone. In order to better characterize the genetic program controlling bone growth, gene expression was analyzed in chondrocytes microdissected from four previously defined zones of the growth plate. This study is the first to examine the growth plate at such resolution and further extends previous work by measuring expression of ~34,000 putative transcripts. We identified significant differences in gene expression among zones in growth plate, which likely contribute to the regulation of chondrocyte maturation in the growth plate.