Differentiation in C2C12 myoblasts depends on the expression of endogenous IGFs and not serum depletion

Myogenic differentiation in vitro has been usually viewed as being negatively controlled by serum mitogens. A depletion of critical serum components from medium has been considered to be essential for permanent withdrawal from the cell cycle and terminal differentiation of myoblasts. Removal of serum mitogens induces the expression of insulin-like growth factors (IGFs), whereas it inhibits that of basic fibroblast growth factor (bFGF) and transforming growth factor (TGF)-β in myoblasts. These responses of growth factors to medium conditioning seem to be well matched to their functions in proliferation/differentiation. In the present study, we showed that C2C12 myoblasts differentiated actively, even in mitogen-rich medium, and that this medium offered an advantage over mitogen-poor medium in terms of increasing differentiation. Our attention focused on endogenous growth factors, as described above, especially IGFs in mitogen-rich medium. During differentiation, IGF-I and IGF-II mRNA levels increased, but bFGF and TGF-β1 mRNAs decreased. Differentiation was commensurable with IGF mRNA levels and suppressed by antisense oligodeoxynucleotides and neutralizing monoclonal antibodies against IGFs. These results suggest that an autocrine/paracrine loop of IGFs, bFGF, and TGF-β1 is active in proliferating and differentiating C2C12 cells without a depletion of serum and that endogenous IGFs actively override the negative control of differentiation by serum mitogens.

In vitro secondary spreading from dissociating blastoderm-derived embryonic tissues of the zebrafish, Brachydanio rerio

Brachydanio rerio (Teleostei: Cyprinidae) blastoderm-derived embryos, deprived of their epidermis in in vitro culture, dissociate and their tissues disperse radially upon the culture substrate. The phenomenon, referred to as secondary spreading, follows primary epidermal membrane formation and dissociation and spans a period from 18 days to 40 days of culture at 24 °C.Secondary spreads and associated cell types and cellular phenomena are described, and medium conditioning, substrate modification, degeneration, and necrosis are discussed.