Schizosaccharomyces pombe Calmodulin, Cam1, Plays a Crucial Role in Sporulation by Recruiting and Stabilizing the Spindle Pole Body Components Responsible for Assembly of the Forespore Membrane

Abstract

Calmodulin in Schizosaccharomyces pombe is encoded by the cam1؉ gene, which is indispensable for both vegetative growth and sporulation. Here, we report how Cam1 functions in spore formation. We found that Cam1 preferentially localized to the spindle pole body (SPB) during meiosis and sporulation. Formation of the forespore membrane, a precursor of the plasma membrane in spores, was blocked in a missense cam1 mutant, which was viable but unable to sporulate. Three SPB proteins necessary for the onset of forespore membrane formation, Spo2, Spo13, and Spo15, were unable to localize to the SPB in the cam1 mutant although five core SPB components that were tested were present. Recruitment of Spo2 and Spo13 is known to require the presence of Spo15 in the SPB. Notably, Spo15 was unstable in the cam1 mutant, and as a result, SPB localization of Spo2 and Spo13 was lost. Overexpression of Spo15 partially alleviated the sporulation defect in the cam1 mutant. These results indicate that calmodulin plays an essential role in forespore membrane formation by stably maintaining Spo15, and thus Spo2 and Spo13, at the SPB in meiotic cells.

The fission yeast SPB component Dms1 is required to initiate forespore membrane formation and maintain meiotic SPB components

“…Previously, we showed that the calmodulin Cam1 regulates the initiation of FSM formation by recruiting the Spo15-Spo2-Spo13 complex to the SPB [ 17 ]. Next, therefore, we examined the behavior of Cam1 in dms1Δ cells.…”

“…So far, seven SPB components required for FSM formation (meiotic SPB components) have been identified: Cam1, Spo2, Spo7, Spo13, Spo15, Ypt2, and Ypt3. During vegetative growth, the coiled-coil protein Spo15 is a component of the single-plaque SPB [ 16 ], and the calmodulin orthologue Cam1 is essential for its localization to the SPB [ 17 ]. The sporulation-specific proteins Spo2 and Spo13 are produced when meiosis is initiated, and are recruited to the cytoplasmic side of the SPB via Spo15.…”

The fission yeast pleckstrin homology domain protein Spo7 is essential for initiation of forespore membrane assembly and spore morphogenesis

“…So far, four meiotic SPB components required for FSM formation have been identified (Takeda and Yamamoto, 1987; Ikemoto et al ., 2000; Nakase et al ., 2008; Itadani et al ., 2010). During vegetative growth, the coiled-coil protein Spo15 is a component of the single-plaque SPB (Ikemoto et al ., 2000).…”

The meiosis-specific nuclear passenger protein is required for proper assembly of forespore membrane in fission yeast

“…The coiled-coil protein Spo15 has been shown to constitutively localize to the SPBs depending on the function of the calmodulin Cam1 (Itadani et al, 2010) and is essential for SPB modifications (Ikemoto et al, 2000). A previous study has reported that Spo2 and Spo13 are sequentially recruited to meiotic SPBs and form a complex with Spo15 to complete this modification (Nakase et al, 2008).…”