Basic fibroblast growth factor induction of neuronal ion channel expression in ascidian ectodermal blastomeres.
1. Cleavage-arrested anterior animal (a4-2) blastomeres isolated from eight-cell embryos of Halocynthia aurantium differentiated into neuronal type cells expressing neuron-specific ion channels when they were treated with basic fibroblast growth factor ( bFGF). This induction process was very similar to that when a4-2 blastomeres were cultured in contact with anterior vegetal (A4-1) blastomeres from the same embryos or when treated with subtilisin, a serine protease. 2. Other growth factors, transforming growth factor (TGF) beta1, activin A, epidermal growth factor (EGF) and nerve growth factor ( NGF), had no effect on the default epidermal differentiation of cleavage-arrested a4-2 blastomeres. 3. Messenger RNA of the ascidian neuronal Na+ channel, TuNa I, was detected using RT-PCR in a4-2-derived partial embryos of Halocynthia aurantium as well as in the cleavage-arrested a4-2 blastomeres treated with bFGF, confirming the neural inducer activity of bFGF during ascidian embryogenesis. 4. bFGF was effective at concentrations as low as 1 ng ml-1 in inducing neuronal ion channels in cleavage-arrested a4-2 blastomeres. EC50 for neuronal differentiation was estimated to be around 8 ng ml-1, and the maximum effect of 90 % neuronalization was obtained with above 100 ng ml-1. 5. For induction of neuronal differentiation, bFGF was required to be continuously present 8 to 14 h after fertilization. A similar time window was required for cell-contact induction, but it was considerably shorter for subtilisin induction. 6. We discuss whether activation of receptor tyrosine kinase is a common pathway for neural induction by bFGF, subtilisin, and cell-contact with A4-1 blastomeres.[1]References
- Basic fibroblast growth factor induction of neuronal ion channel expression in ascidian ectodermal blastomeres. Inazawa, T., Okamura, Y., Takahashi, K. J. Physiol. (Lond.) (1998) [Pubmed]
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