embryogenesis

MOLECULAR BIOLOGY: ON HEDGEHOG PROTEINS: "The progress of organogenesis is governed by patterning processes that have occurred earlier during development and that involve the action of cell-cell signaling pathways, growth factors acting between cells, and transcription factors acting within cells. In general, both body segmentation and brain patterning are essential for conferring a highly organized functional complexity to the body. In both cases, an originally homogeneous group of cells obtains characteristics to give rise to particular structures and functions in a precise spatial and temporal pattern. This produces patterns such as the regular repetition of skeletal elements and the 3-dimensional compartments of brain primordium on which the subsequent complexity of the neuronal network is organized. It is now widely accepted that similar sets of factors are shared by different animal species and also by distinct processes in the course of early patterning of organogenesis. During animal evolution, a 'prepattern' of fundamental organs apparently emerged relatively early."