Matrix proteins synthesis, progression

Once stem cells are committed to the osteoblast lineage, proliferating osteoprogenitors become preosteoblasts, cell growth declines, and there is a progressive expression of differentiation markers by osteoblasts (Stein et al. 1996). Osteoblastic differentiation is characterized by the sequential expression of alkaline phosphatase (ALP), an early marker of osteoblastic phenotype, followed by the synthesis and deposition of collagen type I, bone matrix proteins, and glycosaminoglycans and an increased expression of os-... 

Most of the mitochondrial proteins are nuclear encoded and thus must be targeted into mitochondria and sorted into some of their components after their synthesis at the cytosol. Because mitochondria have two membranes, there are four localization sites the matrix, the inner membrane, the intermembrane space, and the outer membrane (Fig. 6). Although there has been considerable progress in our understanding of these processes, some questions still remain. Moreover, the total picture is rather complicated and contains many exceptions. A simplified view is presented here based mainly on the view of Pfanner and Mihara (Mihara and Omura, 1996 Pfanner et al., 1997 Pfanner, 1998). There are also a number of other excellent reviews on this subject (Schatz, 1996 Stuart and Neupert, 1996 Neupert, 1997 Roise, 1997). 

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