MARKERS OF CELL POLARITY DURING AND AFTER NITROGEN STARVATION IN SCHIZOSACCHAROMYCES-POMBE

In Schizosaccharomyces pombe, nitrogen starvation induces transient ac celeration of cell division and reduction in cell size with a final ar rest in G(1). The division size control appears to be impaired by muta tions in cdr1/nim1 and cdr2, genes that encode protein kinases mediati ng nutritional control over the mitotic cycle, cdr(-) cells arrest aft er fewer rounds of division and are larger than the wild type. Recent work suggests that long-term nitrogen starvation causes S, pombe wild- type cells to become spherical, which suggests loss of cell polarity, cdr mutants retain the elongated shape, indicating a potential differe nce in cell polarity control relative to the wild type. We examined se veral markers related to maintenance of cell polarity in S, pombe foll owing nitrogen starvation including cell division scar pattern and act in and microtubule cytoskeleton. Wild-type cells as well as cdr mutant s maintained a normal cell division scar pattern throughout nitrogen s tarvation but cells dividing under these conditions developed a wall m alformation in the center of the septum. In cells arrested by nitrogen starvation, actin patches, normally associated with sites of cell wal l deposition, were larger and distributed randomly along the cell surf ace. Cytoplasmic arrays of microtubules, which are thought to be invol ved in control of the polarity signal, were not visibly affected. The effects were similar in wild-type cells and in cdr(-) mutants. Upon re feeding, the new growth always reoccurred at the tip zones and there w ere only small deviations of its direction from the original ar;is. Th e results indicate that cell polarity is preserved both in wild-type c ells, which arrest in G(1) and appear spherical, and in cdr1/nim1 and cdr2 mutants, which arrest in G(2) and appear polarized throughout the starvation period.