Control of gene expression during lymphoid development: Targeted gene disruption provides new clues

The expression of structural genes is thought to be regulated by DNA-binding factors interacting with cis-acting regulatory elements. These regulatory elements, identified for many lymphopoietic genes, have served in recent years to identify and clone novel transcription factors. The expression of some of these factors is found to be confined to the lymphoid lineage. This regulated expression in both time and space is thought to mediate entry into and progression along the correct developmental differentiation programs. In recent years, many laboratories have tried to assess the functional relevance of these DNA-binding factors by making use of gene targeting techniques. A review of the results of such knock-out experiments and the consequences for lymphoid development models appears below.