Using 2-3 specific examples, discuss how molecular mechanisms underlie neural development.

Authors Avatar

Using 2-3 specific examples, discuss how molecular mechanisms underlie neural development

   The entire nervous system is derived from ectoderm, but not all ectoderm gives rise to the nervous system. By this token, there must be some mechanism by which some ectodermal cells undergo neural differentiation, and others fail to follow this path, and yield skin epidermis.

   Much research has been done into what determines neural differentiation, or which factors direct the expression of specific genes within individual cells. Two major groups of factors have been described in response to this question: inducing factors; and molecules activated or induced in cells upon exposure to an inducing factor themselves. This latter group relies on the ability of the cell to respond to inductive factors (known as competence), and this depends on the precise repository of receptors etc that is expresses.

   With inducing factors, cells in different positions are going to be exposed to different inducing factors- so it is really the position of the cell in the early on, that is of critical importance in determining its fate.

   Hans Spemann and Hilde Mangold did an experiment whereby the organiser region of the mesoderm (later gives rise to notochord) was transplanted in amphibian embryos. The startling results showed that the second organiser developed into a notochord as it usual, but also the graft had remarkable effect on the surrounding ectoderm of the host- a duplicate body axis and second nervous system developed. This experiment provided evidence that the nervous system development is induced by signal from non-neural cells.

   When ectodermal cells are separated out, in order to prevent any cell-cell signalling, and cultured in the absence of added factors, they form neural tissue. Thus it was realised that neural differentiation is a default pathway for ectodermal cells, and therefore, in non-neural ectodermal cells, the capacity for neural development must be suppressed by signals transferred from neighbouring cells.

Join now!

   The Bone Morphogenic Proteins (BMPs) were found to be mediators of a suppressive signal- Xenopus cells were engineered to express a truncated BMP receptor, so that BMP signalling was blocked. The cells with the altered receptors differentiated into neural tissue, and so blocking BMP is sufficient to trigger neural differentiation from ectodermal cells.

   It was then postulated that the organiser region acts by blocking BMP- hence allowing neural tissue differentiation. The supporting evidence for this theory comes from the identification of Noggin, Follistatin, and Chordin- three major proteins found in the organiser region cells, and able to ...

This is a preview of the whole essay