Regulated secretion of a serine protease that activates an extracellular matrix-degrading metalloprotease during fertilization in Chlamydomonas.

Abstract

Abstract. During fertilization in the biflagellated alga, Chlamydomonas reinhardtii, gametes of opposite mating types adhere to each other via agglutinin molecules located on their flagellar surfaces, generating a sexual signal that induces several cellular responses including cell wall release. This cell contact-generated signal is mediated by cAMP and release of the wall, which is devoid of cellulose and contains several hydroxyproline-rich glycoproteins, is due to the activation of a metalloprotease, lysin. Although we originally assumed that lysin would be stored intracellulady in a compartment structurally separate from its substrate, recently we showed that lysin is stored in the periplasm as an inactive, higher relative molecular mass precursor, prolysin (Buchanan, M. J., S. H.

High-frequency nuclear transformation of Chlamydomonas reinhardtii.

“…When such cells were treated with autolysin, an enzyme normally released by mating Chlamydomonas cells to induce cell-wall removal (19,22), they were transformed at rates similar to cell-wall-deficient (cw-15) derivatives of nit1-305 ( Table 2). The rate of transformation was further enhanced by adding 5% PEG.…”

Mating-Induced Shedding of Cell Walls, Removal of Walls from Vegetative Cells, and Osmotic Stress Induce Presumed Cell Wall Genes in Chlamydomonas

“…A consequence is the activation of flagellar adenylyl cyclase, resulting in a nearly 10-fold increase of intracellular cAMP in each of the interacting gametes (Pasquale and Goodenough, 1987;Saito et al, 1993). This triggers dramatic alterations in the matingcompetent cells (for review, see Pan and Snell, 2000a), among them the release of a matrix-degrading protease named gamete lytic enzyme (GLE) that degrades the gametes' cell wall (Matsuda et al, 1987;Snell et al, 1989;Kinoshita et al, 1992) and the erection of apically localized mating structures (Cavalier-Smith, 1974;Goodenough and Weiss, 1978).…”

Flagellar Adhesion between mt+ and mt− Chlamydomonas Gametes Regulates Phosphorylation of the mt+-specific Homeodomain Protein GSP1

“…Cellular responses associated with activation by cAMP include the following: movement of agglutinin molecules from the plasma membrane of the cell body onto the flagellar membrane to replace agglutinins that are lost as a consequence of adhesion (11)(12)(13); up-regulation of synthesis of agglutinin molecules (11); regulated secretion of a serine protease required to convert a periplasmic prometalloprotease to an active matrix-degrading metalloprotease (14,15); release and degradation of the extracellular matrix (cell wall) (7); activation of apically localized mating structures (7,16); and finally, adhesion and fusion of the cell bodies via the activated mating structures (7,16). Gamete fusion itself generates signals for cellular responses that prepare the new quadriflagellated cell for the zygotic phase of the life cycle.…”

“…Pre-existing flagellar agglutinins are inactivated; synthesis of new agglutinins no longer can be detected; flagella are resorbed; and a new, highly impervious zygote cell wall is assembled (17)(18)(19). Although these responses have been well characterized at the cellular level, few of the molecular events that accompany gamete activation and zygote development have been studied (9,14,15,17,19,20).…”