Biologjia Online

Asymmetric cell division generates cell diversity in all organisms. After asymmetric division, daughter cells acquire distinct cell fates by transcribing different sets of genes. Now, Yoda and colleagues report that LET-19 and DPY-22 – components of the transcriptional Mediator complex – are required for asymmetric division in C. elegans (see p. 1885). They identify mutations in let-19 and dpy-22 that disrupt the asymmetry of T-cell division and cause the symmetrical expression of tlp-1 in T-cell daughters; the normally asymmetric expression of this transcription factor is regulated by Wnt signalling. let-19 and dpy-22, the authors show, encode homologues of MED13 and MED12, components of the Mediator complex, which associates with RNA polymerase to facilitate the activities of various transcription factors. These and other results indicate that, in C. elegans, the Mediator complex regulates not only asymmetric division, as it does in yeast, but also other processes regulated by Wnt signalling.