Morphogenesis

Morphogenesis is the process where cells in a developing embryo move and organize to form specialized structures, organs, and systems. It is stimulated by both chemical and mechanical factors that interact to influence cell behavior and processes.

Morphogens are signal molecules that affect cell behavior, changing internal processes and causing cell migration. Cells respond to morphogens based on their local concentration. Morphogens bind to protein receptors on cell membranes, activating transcription factors that then alter gene expression in the nucleus. This leads to the production of specific proteins that influence cell-to-cell adhesion, extracellular matrix composition, or cellular contraction.

One key way morphogens act is by changing the composition of cell adhesion molecules (CAMs) on cell membranes. Cells tend to aggregate with others that have the same type of CAM molecule, leading to the formation of distinct cell groups and tissues. An example is gastrulation, where morphogens reduce CAMs, allowing cells to detach and move, contributing to the formation of structures like the umbilical vesicle and amnion.

Morphogens can also alter the composition of the extracellular matrix (ECM) surrounding cells. The ECM serves to separate different cell types and create pathways for cell movement. By changing the ECM's composition, morphogens facilitate cell migration from one location to another.

Finally, morphogens can influence cell contraction by stimulating the expression of contractile proteins like myosin and actin. The contraction of these proteins changes cell shape and size, exerting mechanical forces on nearby cells. These mechanical forces can further influence gene expression, cell determination, differentiation, growth, proliferation, and ultimately, morphogenesis.