Progress in 1996

αβ T cells specifically recognize a ligand composed of a peptide bound to a self-major-histocompatibility-complex molecule, but the recognition of slightly altered ligands by T cells can lead to a partial activation. This flexibility is crucial for T-cell development and can have both beneficial and harmful effects on peripheral T cells.

In social insect colonies, workers perform a variety of tasks, such as foraging, brood care and nest construction. As the needs of the colony change, and as resources become available, colonies adjust the numbers of workers engaged in each task. Task allocation is the process that results in specific workers being engaged in specific tasks, in numbers appropriate to the current situation.

Functional studies seem now to confirm, as first suggested by E. Geoffrey Saint-Hilaire in 1822, that there was an inversion of the dorsoventral axis during animal evolution. A conserved system of extracellular signals provides positional information for the allocation of embryonic cells to specific tissue types both in Drosophila and vertebrates; the ventral region of Drosophila is homologous to the dorsal side of the vertebrate. Developmental studies are now revealing some of the characteristics of the ancestral animal that gave rise to the arthropod and mammalian lineages, for which we propose the name Urbilateria.

Genome sequencing is leading to the discovery of new genes at a rate 50–100 times greater than that achieved by classical genetics, but the biological function of almost half of these genes is completely unknown. In order fully to exploit genome sequence data, a systematic approach to the discovery of gene function is required. Possible strategies are discussed here in the context of functional analysis in the yeast Saccfiaromyces cerevisiae, a model eukaryote whose genome sequence will soon be completed.