The filament-forming protein Pil1 assembles linear eisosomes in fission yeast

Abstract

Eisosomes generate spatial domains in the plasma membrane of yeast cells. The core eisosome protein Pil1 is shown to form filaments in vitro and in cells. Pil1 filaments are stable at the cell cortex, and cytoplasmic Pil1 filament rods appear upon overexpression. This shows a role for self-assembly in organizing cortical domains.

Eisosome Ultrastructure and Evolution in Fungi, Microalgae, and Lichens

“…Of the two CAN1 homologues in C. reinhardtii, AOC5 is strongly upregulated in eisosome-free vegetative cells with nitrogen starvation (77), as are other arginine transporters, whereas AOC6 is expressed at constant low levels (ϳ10 reads per kilobase per million mapped reads); expression levels in eisosome-forming C. reinhardtii zygotes have not been evaluated. Sur7p fails to colocalize with eisosomes in S. pombe, whereas Nce102p/Fhn1 is important for their integrity (43), as is also the case in S. cerevisiae (31). Sequences homologous to Sur7p and to the conserved Marvel domain of Nce102p were found in fungi and metazoa but not in any algae.…”

“…S1 in the supplemental material) and Melampsore lini (7), or in parallel or anastomosing rows, as in S. pombe (Fig. 1E) (9,12,43) and Malassezia (12). Interestingly, the punctate eisosomes of S. cerevisiae and C. albicans adopt an elongated anastomosing configuration when the cells are converted to protoplasts (6,44,45), and C. albicans protoplasts restore the punctate configuration when allowed to regrow new walls (45).…”

“…Our studies point to the following six eisosomal features that are encountered across several phyla: (i) a curved, elongated membrane indentation of uniform width (ϳ30 to 50 nm) and depth (ϳ50 nm) that fails to pinch off into vesicles; (ii) the presence of cell wall material in the furrow; (iii) a large-scale topology that can be either punctate or elongated, with the capacity to convert between the two configurations; (iv) "embossed" lipid configurations and IMP endowments that differ from the surrounding plasma membrane; (v) fracture faces that are noncomplementary; and (vi) "flat" versions of the intramembranous domains. In addition, fungal eisosomes tagged with GFP-labeled components are observed to be immobile (16,21,29,35,43), albeit they exhibit subunit turnover (87); the uniform distribution of punctate eisosomes in algae (e.g., see Fig. 7, 9, 10, and 12) suggests that this immobility feature is also conserved.…”

“…In both S. cerevisiae and S. pombe, eisosomes are actively excluded from cellular domains where new cell wall is being laid down, such as small buds, growing tips, and mitotic cleavage planes (9,14,43,78,79), suggesting that they may actually interfere with early fungal wall formation but participate in wall maturation.…”

“…14). These topological alternatives are evidently not conferred by the BAR domain proteins per se: when the S. pombe PIL1 gene is introduced into pil1 mutants of S. cerevisiae, punctate eisosomes are formed; reciprocally, S. pombe mutants rescued with S. cerevisiae PIL1 form elongated eisosomes (43,85). Protoplast fungi have been observed to switch from punctate to elongated and back again (6,44,45), the eisosomes of S. cerevisiae are punctate in growing cells but elongated in ascospores (86), and deletion of the ypr050c gene in S. cerevisiae leads to elongated eisosomes in growing cells (5).…”