Temporal events associated with the onset of expression of several smooth muscle cell (SMC) proteins has been well studied in mouse and avian species. However, the relationship between proliferation and differentiation of smooth muscle cells during embryogenesis have not been explored; nor it is known how recruitment of SMC precursors occurs in the dorsal aorta. In the present study, we have determined the rates of proliferation in developing chick aortae between day 2.5 to 19 and have correlated these data with the expression of various SMC differentiation markers. Two waves of proliferation of aortic SMC precursors were observed; an early phase of rapid proliferation (15-17%) (between days 4 to 12), and a second phase, when replication was reduced to less than 5% (days 16 to hatching). Proliferation of SMC during the first wave occurred concomitantly with the progressive accumulation of SMC contractile proteins, such as SM α-actin, calponin, myosin heavy chain, and the 1E12 antigen. In addition, a ventral-to-dorsal wave in the proliferation of SMC precursors was evident between days 2.5-5. Radial proliferation occurred after embryonic day 6. The proliferation gradient was similar to the previously described differential expression of two early SMC markers: α-actin and the 1E12 antigen. We also found that the overall proliferation within each compartment of the vessel wall, i.e., intima, media, and adventitia varies throughout development. Approximately, 55-63% of all replicating cells were found in the tunica adventitia, from days 6 to 12, whereas 35% were found in the tunica media (tunica media : adventitia = 1:2). This ratio was inverted after day 12, when most of die replicating cells were located in the tunica media (tunica media : adventitia = 2:1 ). The differential proliferation gradient in early stages suggests that a polarity exists either in the in the pool of SMC precursors or in expression of factors that regulate recruitment of presumptive SMC.
|Original language||English (US)|
|State||Published - Dec 1 1997|
ASJC Scopus subject areas
- Molecular Biology