Table 1. New branch formation by budding versus clefting
Cellular mechanismsBuddingClefting
Initiation of new branchesProtrusion of a group of cells outward from an epithelium to generate a new branch tip (in blood vessels, Drosophila trachea, mammary gland, lung, kidney,a and pancreasb)Separation of cells in a preexisting branch tip to generate two or more new branch tips (in salivary gland,c lung, kidney, and pancreasb)
Collective cell migration
 InvasiveDrosophila trachea
Blood vessels
 Noninvasive Mammary gland
Lung (?)
Kidney (?)
Patterned cell proliferation
 Regionalized proliferationLung
Kidney
 Oriented cell divisionLung
Kidney (?)
Actomyosin contractilityNot required in blood vessels and lung Salivary gland, kidney,
Required in mammary gland (?) and pancreasblung, pancreasb
Differential cell motilitiesMammary glandSalivary gland
PancreasbPancreasb
Physical constraint
 By basement membraneSalivary gland
 By smooth muscle cellsLung

—, not yet described or established.

  • a Ureteric bud in kidney.

  • b Mechanisms of pancreas branching may be complex, including a unique process involving the formation of microlumens.

  • c Submandibular salivary gland.