User:Jtwsaddress42/Projects/Project 2/Sections/Chapter 10/The Molecular Anchors - Substrate, Extracellular Matrix, & Neighboring Cell Adhesion

There are a number of pre-requisites for multicellularity, not the least of which is the ability to stick together. But just because cells stick together, doesn't mean cells stay stuck together and protozoan cells possess mechanisms for selectively engaging and disengaging adhesion mechanisms via the mechano-chemistry of membrane-embedded proteins.

Important adhesion molecules that needed to be acquired by our protozoan ancestors prior to the origins of animals include: catenins, integrins, and cadherins that facilitate cell-cell adhesion. Also important are substrate adhesion molecules used for selective-anchoring to surfaces in the environment, as well as extracellular matrix (ECM) proteins that provide additional scaffolding for the multicellular population organize itself on. Cavalier-Smith will trace these innovations to adaptations in locomotion, feeding, reproduction, social, and life-cycle organization.

Integrins are used by epithelial cells to attach themselves to the extracellular matrix and appear to have emerged in the line of Sulcozoa with psuedopodia that leads to Choanocytes and animals.