In the fission yeast S. pombe, gametogenesis occurs through a process referred to as sporulation. In this process, each of the haploid nuclei that is generated during meiosis becomes encapsulated by the forespore membrane (FSM), which ultimately forms the plasma membrane of the newly formed gametes. A number of proteins are known to be crucial for FSM assembly and sporulation. These include actin and actin regulators, as well as components of the septation initiation network (SIN). Here, Hongyan Yan and Mohan Balasubramanian (p. ) investigate the roles of these proteins in the sporulation process and show that, during sporulation, F-actin assembles into four ring-like structures: the meiotic actin rings (MeiARs). Assembly, maintenance and constriction of MeiARs, as well as the correct spore formation, require Arp2/3 and the formin For3, known actin nucleators. In addition, actin polymerisation is necessary for the recruitment of these and other proteins to the leading edge – the ring-like structure that guides FSM assembly – and that loss of the actin ring leads to an excessive assembly of deformed FSMs. Furthermore, a fully functional SIN is required for the closure of MeiARs during sporulation. Together, these data highlight a crucial role for these actin rings in recruiting the protein complement that is required for sporulation, and in promoting FSM assembly and spore formation.
