The epithelium lines the cavities and surfaces of glands and many organs and secretes enzymes and other factors that are essential to the function of these tissues.

The mesenchyme is the connective tissue in embryos.

In the 1950s, scientists discovered that the epithelium takes its developmental instructions from the mesenchyme.

For example, when researchers put bladder epithelial cells on the mesenchyme of a prostate gland, the bladder cells were changed into prostatic epithelium. The prostatic mesenchyme had altered the fate of the bladder.

'The mesenchyme - it's the director; it's controlling the show,' said University of Illinois (U-I) veterinary biosciences professor Paul Cooke, who led the new study with researcher Liz Simon.

These findings have been described in Stem Cells.