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

LUCÍA DURRIEU, ALAN BUSH Y ALEJANDRO COLMAN-LERNER

Villa Carlos Paz, Argentina

Congreso; Reunión anual de SAIB; 2008

SAIB

<!-- /* Font Definitions */ @font-face {font-family:"Cambria Math"; panose-1:2 4 5 3 5 4 6 3 2 4; mso-font-charset:0; mso-generic-font-family:roman; mso-font-pitch:variable; mso-font-signature:-1610611985 1107304683 0 0 159 0;} @font-face {font-family:Calibri; panose-1:2 15 5 2 2 2 4 3 2 4; mso-font-charset:0; mso-generic-font-family:swiss; mso-font-pitch:variable; mso-font-signature:-1610611985 1073750139 0 0 159 0;} /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-unhide:no; mso-style-qformat:yes; mso-style-parent:""; margin-top:0cm; margin-right:0cm; margin-bottom:10.0pt; margin-left:0cm; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-fareast-font-family:Calibri; mso-bidi-font-family:"Times New Roman"; mso-fareast-language:EN-US;} .MsoChpDefault {mso-style-type:export-only; mso-default-props:yes; font-size:10.0pt; mso-ansi-font-size:10.0pt; mso-bidi-font-size:10.0pt; mso-ascii-font-family:Calibri; mso-fareast-font-family:Calibri; mso-hansi-font-family:Calibri;} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> One of the mechanisms of cellular differentiation is asymmetric division, a process in which one cell divides to produce two different daughter cells due, for example,to asymmetric segregation of mRNAs or proteins that determine cell fate. We study one case of asymmetric gene expression in the yeast S.cerevisiae. Yeast cells form buds that separate to become daughters. Daughters and mothers are genetically identical but constitute distinct cell types. Early in the G1 phase of the cell cycle, at least eight genes are induced only in the daughter cell. Expression is controlled by the transcription factor Ace2, which enters both nuclei at the end of mitosis, but is soon re-exported from 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 nuclear envelopes 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- daughter asymmetric gene expression correctly. These results indicate that Ace2 is a better cargo of the mother export machinery and suggest that other cargoes might also be differentially exported, revealing a new source of cellular differentiation.