Last revised: 19 January 2024
Part 1 of this series discussed the basics of metastatic disease.
Part 2 discussed features of human biology that are important in understanding cancer and metastases.
Part 3 discussed basic principles of how these features are altered during the development of cancer and metastases, with specifics to be discussed in parts 3a through 3d.
Part 3a discussed normal (physiologic) cell division and how this cell property is altered during malignant transformation.
Part 3b-1 discusses normal cell migration. Related discussions for nonscientists are at
- Cell migration in the embryo and fetus (how metastases arise, part 3b-1a)
- Cell migration in children and adults (how metastases arise, part 3b-1b)
Cell migration is an evolutionarily conserved activity essential for development and function in humans, particularly for embryogenesis, wound healing, immune response and blood vessel formation (Kurosaka 2008). Its major components have been functionally conserved in evolution for over a billion years, from protozoa (single celled organisms) to mammals (Kurosaka 2008). Cells migrate individually or collectively (i.e., as sheets or clusters of cells).
What cells migrate?
The migration of cells over short and long distances determines their correct positioning during embryonic organogenesis and in adult tissues and organs:
Migration defects during embryogenesis cause severe embryonic malformations, including early embryonic death, neurological disorders, congenital heart disease and physical and mental retardation (Kurosaka 2008).
Migration is physiologically normal for these conditions and cells:
The blastula reorganizes into the gastrula, which develops 3 germ layers: the ectoderm, endoderm and mesoderm. The archenteron is the primitive digestive tract that develops into endoderm and mesoderm.
Migration of cells in 3 germ cells occurs in the embryo and fetus.
This diagram shows the adult equivalents of these locations.
- During early stages, neuronal precursors of the neural crest lineage follow the same migration mechanisms as other mesenchymal cells but after differentiation, neuronal cell bodies become stationary and only their neurites migrate (Kurosaka 2008).
Migrating neuronal cells
Migration of cells to the adrenal medulla.
Primordial germ cells (PGC) originate in the allantois, part of the placenta, and migrate to the genital ridges. They rarely migrate to the brain and can cause tumors.
Wound closure is characterized by migration of neutrophils, macrophages and epithelial cells (Leoni 2015).
Epithelial cells are connected to each other by various mechanisms, which prevent epithelial cell migration under standard conditions.
Migration of small intestinal epithelium from the crypts to the tip of the villi.
Stem cell behavior is controlled by their cellular, chemical and physical components.
White blood cells migrate from blood vessels into infected tissues to destroy pathogens.
Neutrophils migrate from the central vessel into surrounding tissue.
Migrating white blood cells
Migrating mesenchymal stem cells
Trafficking of hematopoietic stem and progenitor cells in fetal life and during adulthood.
Part 3b-2 will discuss normal triggers of migration and the mechanics of cell migration.