Evidence for a functional membrane barrier in the transition zone between the flagellum and cell body of Chlamydomonas eugametos gametes

Abstract

Evidence is presented which supports the concept of a functional membrane barrier in the transition zone at the base of each flagellum of Chlamydomonas eugametos gametes. This makes it unlikely that agglutination factors present on the surface of the cell body can diffuse or be transported to the flagellar membrane. The evidence is as follows: 1) The glycoprotein composition of the flagellar membrane is very different to that of the cell-body plasma membrane. 2) The flagella of gametes treated with cycloheximide, tunicamycin or α, α'-dipyridyl become non-agglutinable but the source of agglutination factors on the cell body is not affected. 3) Even under natural conditions when the flagella are non-agglutinable, for example in vis-à-vis pairs or in appropriate cell strains that are non-agglutinable in the dark, the cell bodies maintain the normal complement of active agglutinins. 4) When flagella of living cells are labeled with antibodies bound to fluorescein, the label does not diffuse onto the cell-body surface. 5) When gametes fuse to form vis-à-vis pairs, the original mating-type-specific antigenicity of each cell body is slowly lost (probably due to the antigens diffusing over both cell bodies), while the specific antigenicity of the flagellar surface is maintained. Even when the flagella of vis-à-vis pairs are regenerated from cell bodies with mixed antigenicity, the antigenicity of the flagella remains matingtype-specific. 6) Evidence is presented for the existence of a pool of agglutination factors within the cell bodies but not on the outer surface of the cells.

Characterization of Blue Light Signal Transduction Chains That Control Development and Maintenance of Sexual Competence in Chlamydomonas reinhardtii

“…Rather, we speculate that light reactivates agglutinin molecules on the flagella by some chemical modification, e.g. distantly related species (Kooijman et al, 1986(Kooijman et al, , 1988 A model that summarizes our data on the light signal transduction cascade that controls gamete formation and the reactivation of dark-inactivated gametes is presented in Figure 10. We propose that the conversion of pregametes to gametes and the reactivation of dark-inactivated gametes are controlled by two independent light-signaling pathways.…”

“…Agglutinins are Iocalized on ff agelIa (ff agellar agglutinin) and the cell body (cell body agglutinin) (Saito et al, 1985;Musgrave et al, 1986;Hunnicutt et al, 1990). After an incubation of gametes with cycloheximide for 6 h, active flagellar agglutinin disappeared, whereas a significant amount of cell body agglutinin remained (Fig.…”

Regulated Targeting of a Protein Kinase into an Intact Flagellum

“…There is compelling evidence that intraflagellar transport is responsible for carrying flagellar precursors into newly forming flagella and for returning flagellar components to the cytoplasm during flagellar resorption. It is likely that this system also is involved in the constitutive turnover of flagellar components in intact cilia/flagella (78,(81)(82)(83)(84), although other motility mechanisms also may play a role (6,13,85).…”

“…One of the earliest documented steps in gamete activation triggered by agglutinin interactions is activation of a gamete-specific flagellar adenylyl cyclase and generation of cAMP (7-11). As part of an intricate feedback mechanism required to maintain and enhance flagellar adhesiveness and to keep the cells bound to each other until cell-cell fusion occurs, cAMP levels increase in the cell bodies of the gametes of both mating types during flagellar adhesion and lead to increased flagellar adhesiveness (6,9,12,13).The increased cellular levels of cAMP also induce additional events in the cell body, including regulated secretion of molecules required for release and degradation of the extracellular matrix (cell wall), activation of fusion organelles called mating structures on the apical ends of the interacting cells between their sets of flagella, and phosphorylation of an mtϩ gametespecific homeodomain protein, GSP1 (14, 15). Adhesion and fusion of the mating structures on the mtϩ and mtϪ gametes are followed by complete merging of the two cell bodies.…”

“…One of the earliest documented steps in gamete activation triggered by agglutinin interactions is activation of a gamete-specific flagellar adenylyl cyclase and generation of cAMP (7-11). As part of an intricate feedback mechanism required to maintain and enhance flagellar adhesiveness and to keep the cells bound to each other until cell-cell fusion occurs, cAMP levels increase in the cell bodies of the gametes of both mating types during flagellar adhesion and lead to increased flagellar adhesiveness (6,9,12,13).…”