The early process of vertebrate neurogenesis is divided into several basic processes, such as differentiation into the neural plate (neural induction) and formation and maturation of the neural network from the ectoderm. This early process includes occurrence of neural precursor cells, pattern formation of the nervous system, and proliferation and differentiation of neural precursor cells.
It is known that the early neurogenesis of Xenopus laevis is induced by blockade of BMP4 (i.e., Bone Morphogenetic Protein 4) signals by noggin, chordin, etc. (Sasai et al., Nature, 376:333 [1995]; and Mizuseki et al., Development 125:579-587 [1998]). BMP4 is a factor which induces the ectoderm into epidermal cells. When BMP4 is activated, cells differentiate into the epidermis. Proneural genes (e.g., Neurogenin, NeuroD, XASH-3, XATH-3) which are involved in the control of neural induction (i.e., neurogenesis, neural differentiation) and in the coding for basic helix-loop-helix (bHLH) transcription factors are also known. However, the factors involved in the blockade of BMP4 signals to proneural genes are still unknown.
Understanding the molecular basis of higher brain functions is important, not only to elucidate the universal principle of these processes, but also in the development of new therapeutic methods for treatment of diseases involving brain functions (i.e., neurogenesis).