Gene expression, hierarchy

Figure 1. Hierarchy of control of gene expression. A total of about 50,000 to 100,000 genes are necessary to encode a mammal, most of which encode housekeeping, structural component, or terminal differentiation gene products. Transcription factor genes regulate expression of the lower-level genes and are in turn controlled by other upper-level transcription factors.

Besides AHLs (Table 1), the opportunistic human pathogen Pseudomonas aeruginosa also produces another chemically distinct QS signal molecule, 2-n-heptyl-3-hydroxy-4(lH)-quinolone (PQS 5) [18]. PQS is an integral component of the QS hierarchy and plays an important role in regulating virulence gene expression [19]. 

It seems likely that the pivotal events in the evolution of a differentiated cell reflect changes in gene expression that result from a complex hierarchy of controls. The key to understanding differentiation, therefore, is to identify the regulatory factors responsible for the controls involved in differentiation and to explain how they act. 

Brady G, BilUa F, Knox J, Hoang T, Kirsch IR, Voura EB, Hawley RG, Cumming R, Buchwald M, Siminovitch K. Analysis of gene expression in a complex differentiation hierarchy by global ampU-fication of cDNA from single cells. Curr. Biol. 1995 5 909-922. 

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