THE NUCLEAR ENVELOPE DIFFUSION BARRIER IS REQUIRED FOR CORRECT MOTHER-DAUGHTER ASYMMETRIC GENE EXPRESSION IN YEAST

LUCÍA DURRIEU; ALAN BUSH; ALEJANDRO COLMAN-LERNER

Congreso; Reunión de la SAIB; 2008

SAIB

One of the mechanisms of cellular differentiation is asymmetric division, a process in which onecell divides to produce two different daughter cells due, for example, to asymmetric segregationof mRNAs or proteins that determine cell fate. We study one case of asymmetric gene expressionin the yeast S.cerevisiae. Yeast cells form buds that separate to become daughters. Daughters andmothers are genetically identical but constitute distinct cell types. Early in the G1 phase of the cellcycle, at least eight genes are induced only in the daughter cell. Expression is controlled by thetranscription factor Ace2, which enters both nuclei at the end of mitosis, but is soon re-exportedfrom the mother nucleus. The source of asymmetry remains unknown. Recently, Scheprova et al(2008) described a lateral diffusion barrier between the mother and the growing bud nuclearenvelopes that limits the translocation into the bud of all external nuclear membrane proteins,including the nuclear pores. Here we show, using quantitative time-lapse fluorescence microscopy,that cells delta-bud6, which are defective in this barrier, fail to establish mother- daughterasymmetric gene expression correctly. These results indicate that Ace2 is a better cargo of themother export machinery and suggest that other cargoes might also be differentially exported,revealing a new source of cellular differentiation.