Sporulation in yeast
Our group is interested in the various cellular processes that underlie the sexual cycle of budding yeast [mating and meiosis]. In the past we have addressed the meiosis specific pathways that regulate spore morphogenesis with respect to spindle pole body function, membrane formation and morphogenesis and cytokinesis (Figure 1 and Figure 2). We mainly focused on the processes that regulate spore morphogenesis in comparison to cell division by bud formation. Among others, we concentrated on the regulation of spindle pole function in controlling vesicle fusion and in the initiation of spore morphogenesis and on membrane shaping of the spore.
This picture shows a cell in meiosis II in the progress of forming 2 spores (yellow), which relies on the selective activation of 2 spindle pole bodies (green). more …
The making of spores is costly – but nutrients are limited.
Therefore yeast invented a way to precisely control the number of spores according to available nutrients.
This picture shows a cell in meiosis II in the progress of forming 2 spores (yellow), which relies on the selective activation of 2 spindle pole bodies (green).
A self-organizing mechanism ensures that spindle pole body activation is binary (bistable: either active or inactive) and irreversible. Under conditions of nutrient limitations, only two spores are formed. In this case always one spindle pole body per meiosis II spindle (red) becomes activated. This ensures a higher degree of transmission of maternal genetic diversity as it would be the case of the random situation.
How yeast makes spores
Meiosis and sporulation is conducted as a response to adverse environmental conditions.
Thereby, spores are made to protect the cells, whereas meiosis generates new genetic variability – to prepare for the unknown.
The spore assembly pathway of yeast.
(A) Spore assembly starts in meiosis II with the docking of secretory vesicles to a meiosis-specific modification of the spindle pole body.
(B) Secretory vesicles fuse in a regulated manner with each other and form the prospore membrane.
(C) This membrane subsequently enlarges and engulfs the nuclei that are formed during meiosis II.
(D) Upon cytokinesis, the leading edge protein coat at the forefront of the membrane is removed. This leads to prospore membrane closure and thereby to the formation of new compartments – the spores – within the cytoplasm of the mother cell.