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Ultra-violet (u.v.) irradiation of the vegetal pole of newly fertilized eggs has three documented effects: reduction of primordial germ cells (PGCs), cytological damage to the vegetal hemisphere and disruption of the normal mechanism by which the vegetal yolk mass induces the formation of the dorsal axis of the embryo. In this study, we find that 90° rotation of the egg for various periods after irradiation rescues the dorsal axial structures but does not restore the number of PGCs found in the dorsal mesentery of the gut; neither is there any correlation between reduced numbers of PGCs and disruption of cleavage at the vegetal pole. We therefore conclude that the effect on the germ line is separate from the other two phenomena. Secondly, 90° rotation of non-irradiated eggs was found to significantly reduce germ cell numbers migrating in the dorsal mesentery of the gut.

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Running title: Asymmetric secretion enforces daughter state Abbreviations: Endoplasmic reticulum (ER) Concanavalin A (ConA) Mother Enrichment Program (MEP) Monomeric superfolder GFP (msGFP) Chitin Binding Domain (CBD) Plasma membrane (PM) TOC Summary:Asymmetric segregation of the transcription factor Ace2 drives daughter-specific cell separation after cytokinesis. Cells engineered to express Ace2 targets symmetrically produce the cell separation enzyme Cts1. However, secretion 2 remains asymmetric suggesting other daughter-specific factors are required to reinforce the daughter cell identity. AbstractAsymmetric segregation of cellular factors during cell division produces two cells with different identities. This asymmetry underlies cell fate decisions as well as the ability to self-renew. Asymmetric segregation of protein and RNA to the growing bud of Saccharomyces cerevisiae generates a daughter cell with features distinct from its mother. For example, asymmetric segregation of the transcription factor Ace2 to the newly formed daughter cell activates a gene expression program unique to daughters. Ace2 activates a cohort of genes, including degradative enzymes, which facilitate cell separation exclusively from the daughter. This asymmetric secretion leaves a characteristic 'bud scar' chitin ring on the mother. We sought to determine the sufficiency of Ace2 to define a daughter cell state by generating an ACE2 allele which localizes to both mother and daughter nuclei. When Ace2 asymmetry is lost, Ace2 target gene transcription and translation occur in both mother and daughter cells. However, we find that mother cells retain bud scars and maintain asymmetric daughterspecific secretion of the wall degrading enzyme Cts1. These findings demonstrate that while mothers are competent to transcribe and translate Ace2 targets, additional intrinsic factors reinforce the daughter cell state.