Extracellular Matrix Proteins, Basement Membranes And The Glycocalyx
Sometimes there is no doubt that scientists do not make life easy for themselves. A case in point concerns what zoologists call the ‘material’ present outside an animal cell. Botanists have it pretty easy – a plant has a cell wall; this is Botany 1.01, as they say.
And an animal cell has … what exactly?
Well, please choose from the following: basement membrane, basal lamina, extracellular matrix and glycocalyx. Don’t worry, you will get a point whatever you say.
Some of the problem here is of semantics, some of history (light microscopy v. electron microscopy) and some of the problem is because not enough heads have been banged together!
Basically, the glycocalyx (also called the cell coat) consists of intrinsic membrane glycoproteins and glycolipids that have carbohydrate portions protruding from the plasma membrane. This is why this is also called a ‘sugar coat’ (just what we need, another name!). However, these moieties are also intimately associated with glycoproteins and proteoglycans that have been secreted by said cells into the extracellular space. Many, if not most, of these adsorbed molecules can also be considered to be part of the extracellular matrix.
Basal laminae are thin flexible mats of specialised extracellular matrix that underlie all epithelial cell sheets and tubes as well as coating muscle, fat and Schwann cells and are generally said to be around 40-120 nm thick. Mind you, specialised electron microscopical staining techniques can give provide glycocalyx measurement in excess of this! The so-called basement membranes are also specialised sheets of extracellular matrix, and therefore synonymous with basal laminae – except they are not, of course, membranes in the sense of being built around a lipid bilayer.
So: best to remember that there is a lot going on ‘outside’ an animal cell as well as a plant cell – in fact trying to consider where a cell membrane ‘stops’ becomes slightly redundant thinking. However, it does emphasise how important this ‘region’ is and why we should give due recognition to the function of specialised basement membrane proteins, such as collagen IV, fibronectin, vitronectin, entactin, heparin sulfate (a proteoglycan).
These molecules help anchor epithelium and connective tissue, and are involved in angiogenesis and endothelial cell differentiation. The ‘basement membrane’ can also act as a storage site for growth factors, filter and be part of a mechanical barrier and buffer. There is an awful lot going on here and we probably have not touched upon the half of it.
The availability of purified basement membrane extracts (BMEs), as available in the Cultrex range from amsbio, helps considerably in our research efforts. Used in conjunction, with 3D culturing in particular we should make real advances in our knowledge of the function of the glycocalyx, basement membrane and extracellular matrix!
Date added: 2015-05-25 12:08:41