Genomics and evolution of murine homeobox genes

Summary

Introduction

One thousand genes have now been mapped to the human genome. No obvious patterns of gene arrangement are as yet apparent. However, an important conclusion can be drawn from the provisional data already available. Numerous genes which exhibit coordinated expression are frequently unlinked, and in fact, may reside on different chromosomes. This is the case for the collagen gene family, for example, and many other similar examples exist in man as well as the mouse Mus musculus, where comparable gene mapping data exists (de la Chappelle, 1985).

The coordinated expression of unlinked genes, while not ruling out the cis regulation of tightly linked genes, does imply the existence of transacting regulatory factors. It can be assumed that such factors exist as DNA binding proteins. This assumption seems reasonable, since in lower eukaryotes as in yeast, such transregulatory systems have been clearly demonstrated.

Transregulatory systems may assume at the least two general forms: network and hierarchical. In the first, one assumes that the products of genes within a system are cross regulating according to cybernetic design. The activity of one gene is communicated to all other gene members of the set, ensuring overall coordination. In the network system, one imagines that the gene members encode both regulatory and functional (in the sense of enzymatic or structural) gene products. In the second or hierarchical system, one imagines a class of controller gene or genes that regulate a second set of ‘functional’ genes. The controller gene(s) would thus orchestrate the expression of genes that operate at some functional level.