Curb coterie from which specialised units develop (4,4)
I believe the answer is:
stem cell
'from which specialised units develop' is the definition.
'curb coterie' is the wordplay.
'curb' becomes 'stem'.
'coterie' becomes 'cell' (both can mean a group of people).
'stem'+'cell'='STEM CELL'
(Other definitions for stem cell that I've seen before include "Versatile building block of life" , "Undifferentiated functional unit in an organism" , "Undifferentiated unit of life" , "Generalised producer in living organism" , "biological germ" .)