Analysis of the structural genes encoding M-factor in the fission yeast Schizosaccharomyces pombe: identification of a third gene, mfm3.

Abstract

We previously identified two genes, mfinl and mfin2, with the potential to encode the M-factor mating pheromone of the fission yeast Schizosaccharomyces pombe (J. Davey, EMBO J. 11:951-960, 1992), but further analysis revealed that a mutant strain lacking both genes still produced active M-factor. Here we describe the isolation and characterization of a third M-factor gene, mfm3. A mutant lacking all three genes fails to produce M-factor, indicating that all functional M-factor genes now have been identified. The triple mutant exhibits an absolute mating defect in M cells, a defect that is not rescued by addition of exogenous M-factor. A mutational analysis reveals that all three mJfm genes contribute to the production of M-factor. Their transcription is limited to M cells and requires the matl-Mc and stell gene products. Each gene is induced when the cells are starved of nitrogen and further induced by a pheromone signal. Additionally, the signal transduction machinery associated with the pheromone response is required for transcription of the mfm genes in both stimulated and unstimulated cells.The fission yeast Schizosaccharomycespombe exists in one of two mating types, minus (M) or plus (P), and under the appropriate conditions, cells of opposite mating type can conjugate to form a diploid zygote (reviewed in reference 45). Prior to conjugation, the cells communicate with each other via diffusible mating pheromones that prime the recipient cell for mating; M cells release M-factor, which prepares P cells for mating, and P cells secrete P-factor, which stimulates M cells. Pheromone-induced changes include a G1 arrest of the cell cycle (9, 26), an altered pattern of gene transcription (46), and elongation of the cell (7,19,36).The response begins when the pheromone binds to a Gprotein-coupled receptor on the surface of the target cell; receptors for P-factor are encoded by the mam2 gene (29), while those for M-factor are encoded by map3 (58). Stimulation of the receptor is thought to cause dissociation of the G protein such that the Got subunit (encoded bygpal [49]) is able to trigger an intracellular signalling pathway which includes a cascade of protein kinases encoded by the byrl, byr2, and spkl genes (42,44,56,59,61). A number of these enzymes are functionally homologous to the mitogen-activated protein kinases believed to be involved in controlling the proliferation and differentiation of mammalian cells (reviewed in reference 16). Transmission of the pheromone signal also requires the rasl gene product, the S. pombe homolog of the mammalian ras oncogene (20,46).The M-factor pheromone is a nonapeptide in which the C-terminal cysteine residue is S farnesylated and carboxyl methylated (7,8,60); P-factor is a peptide made of 23 residues and is probably unmodified (26). Although the biogenesis of M-factor is not fully characterized, it is likely to be similar to * Corresponding author. Mailing address:

Spatial focalization of pheromone/MAPK signaling triggers commitment to cell–cell fusion

“…S2A-E). This is consistent with the previous observations that expression of pheromones and their receptors is induced by starvation (Kitamura and Shimoda 1991;Tanaka et al 1993;Kjaerulff et al 1994). In contrast, upon nitrogen starvation, these autocrine cells spontaneously activated pheromone signaling, as reported previously (Tanaka et al 1993): They stopped dividing and expressed pheromone-responsive gene products such as the pheromone transporter Mam1, the pheromone-dependent formin Fus1, and the replaced pheromone receptor Map3 (Supplemental Fig.…”

“…The finding that S. cerevisiae cells expressing reduced levels of a-factor pheromone are specifically fusion-defective (Brizzio et al 1996) suggests that pheromones may form such chemical signals. However, addition of exogenous pheromone to cells unable to secrete it does not restore fusion ability (Michaelis and Herskowitz 1988;Kjaerulff et al 1994;Seike et al 2013). Individual cells exposed to even saturating pheromone levels also do not lyse (which would result from a fusion attempt without a partner cell), suggesting that the decision to fuse requires more than a simple step increase in pheromone signaling.…”

A pheromone mutant of Schizosaccharomyces pombe displays nucleolar fragmentation

“…In S. pombe, three genes (mfm1, mfm2, and mfm3) encoding for the M-factor have been sequenced (22,23). Among these genes, we selected the mfm1 gene as a probe for our Northern analysis, because its expression is greatly induced by nitrogen starvation (data not shown).…”

Molecular coevolution of a sex pheromone and its receptor triggers reproductive isolation in Schizosaccharomyces pombe

“…The mating pheromones of S. pombe are small peptides that play essential roles in the courtship reaction. The M-factor pheromone, YTPKV-PYMC Far -OCH 3 , is a C-terminally farnesylated nonapeptide secreted by M cells (12)(13)(14) that is specifically recognized by a G-proteincoupled receptor, Map3, on the surface of P cells (15). P factor, the mating pheromone secreted by P cells, is a simple peptide composed of 23 amino acids that activates the corresponding receptor, Mam2, on M cells (16,17).…”

“…The primary structures of both mating pheromones and their receptors can be easily altered by in vitro mutagenesis. Because mating competence depends on signaling by both the M-and P-type pheromones, complete impairment of M-factor signaling should prevent the mating reaction (13,(15)(16)(17).…”