Meiotic targets of the Ras/cAMP/PKA pathway during regulation of spore formation in Saccharomyces cerevisiae

Sporulation in Saccharomyces cerevisiae occurs in response to starvation for nutrients and in presence of a non-fermentable carbon source like potassium acetate which lead diploid yeast cells to undergo meiosis and subsequently to package the haploid nuclei in ascospores. The number of formed spo...

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Bibliographic Details
Main Author: Muscó, Massimiliano
Contributors: Taxis, Christof (PD Dr.) (Thesis advisor)
Format: Dissertation
Language:English
Published: Philipps-Universität Marburg 2017
Biologie
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Summary:Sporulation in Saccharomyces cerevisiae occurs in response to starvation for nutrients and in presence of a non-fermentable carbon source like potassium acetate which lead diploid yeast cells to undergo meiosis and subsequently to package the haploid nuclei in ascospores. The number of formed spores is between one and four and depends on the availability of nutrients, the more nutrients are available the higher is the number of spores per ascus. This regulation of the spore numbers is called spore number control (SNC) and occurs at the yeast centrosome called spindle pole body (SPB). A meiotic placque (MP) which works as scaffold to initiate the synthesis of the prosporemembrane, is composed by three essential proteins Mpc54, Mpc70 and Spo74. The regulation of spore number is controlled by nutrients which according to the concentration of potassium acetate (KOAc) regulate the amount of MP proteins and by the spindle polarity which is the basis for adaptation of gamete numbers during meiosis, the age of the SPBs indeed is crucial for the selection of the SPBs to modify and that will become spores. The protein Ady1 is phosphorylated by the kinase PKA in vitro. Ady1 has a genetic interaction with the SPB components and localizes all the MP components to the SPBs, it is responsible then of the formation and the activity of the MP. The nutrient-responsive Ras/cyclic AMP (cAMP)/protein kinase A (PKA) pathway influences proliferation, carbohydrate metabolism, entry into meiosis and gamete numbers in response to nutrients in Saccharomyces cerevisiae. In this study, it was shown how Ras/cAMP/PKA signal transduction pathway influences the adjustment of spore numbers to external nutrients. Specifically, low PKA activity increased the spore formation by increasing the abundance of two MP proteins Mpc70 and Spo74 plus Ady1 when the source of potassium acetate is poor. The approach which has been used to induce high PKA prevented spore formation, many cells did not reach the meiotic divisions. Nevertheless, by this method it was possible to see that the Mpc54 protein encoded by the early gene MPC54 is affected in its abundance as well. My assays revealed that all these players are in vivo targets of PKA. Mpc54, Mpc70 as well as the meiotic protein Ady1 could be indirectly targets of PKA. The data suggested that Spo74, is a direct target of PKA and this direct regulation contributed to spore number control. PKA activity as well affected the timing of meiotic entry, cells entered meiosis earlier when PKA was reduced. The collected data indicated that inactivation of the transcription factor Nrg1 reduces spore formation. Yet, high PKA activity affected negatively the plasma membrane localization of Ras proteins during vegetative growth and sporulation. Finally, it has been shown that the activity of PKA controls the activity of other components like the nucleolar protein Fob1, the regulatory subunit of Snf1 called Snf4 and the nicotinamidase Pnc1. Overall, the findings imply the involvement of the Ras/cAMP/PKA pathway in the regulation of gamete numbers during yeast meiosis.
Physical Description:151 Pages
DOI:https://doi.org/10.17192/z2017.0777