Temporal and spatial expression of a growth-regulated network of imprinted genes in growth plate

In mammals, the somatic growth rate is rapid during fetal and early postnatal life and then gradually declines and eventually stops. In search of the fundamental biological mechanism causing coordinated growth deceleration in multiple tissues, a network of imprinted genes was recently identified based on a coordinated decline in expression in several organs during postnatal growth. To explore a possible role in longitudinal bone growth, we characterized expression of the network during postnatal growth in microdissected metaphyseal bone and growth plate zones of 1-, 3-, and 9-week-old rats using real-time PCR. The expression pattern of the network is modified in growth plate. Similar to the coordinated decline previously observed in kidney, lung, liver, and heart, expression of all genes, except Gtl2, decreased with age in metaphyseal bone. On the contrary, Mest, Dlk1, H19, and Gtl2 decreased, and Cdkn1c, Grb10, and Slc38a4 increased with age in growth plate. During differentiation from resting to hypertrophic zone, Mest, Dlk1, Grb10, and Gtl2 expression decreased, whereas Slc38a4 expression increased. In particular, developmental changes in the expression of growth-promoting genes, Mest, Dlk1, Gtl2, and growth-inhibitory genes, Cdkn1c and Grb10, may contribute to the decline in longitudinal bone growth that occurs with age.