A nucleus-basal body connector in Chlamydomonas reinhardtii that may function in basal body localization or segregation.

Abstract

We have isolated a nucleus-basal body complex from Chlamydomonas reinhardtii.The complex is strongly immunoreactive to an antibody generated against a major protein constituent of isolated Tetraselmis striata flagellar roots (Salisbury, J. L., A. Baron, B. Surek, and M. Melkonian, J. Cell Biol.,. Electrophoretic and immunoelectrophoretic analysis indicates that, like the Tetraselmis protein, the Chlamydomonas antigen consists of two acidic isoforms of ~20 kD. Indirect immunofluorescent staining of nucleus-basal body complexes reveals two major fibers in the connector region, one between each basal body and the nucleus. The nucleus is also strongly immunoreactive, with staining radiating around much of the nucleus from a region of greatest concentration at the connector pole. Calcium treatment causes shortening of the connector fibers and also movement of nuclear DNA towards the connector pole. Electron microscopic observation of negatively stained nucleus-basal body complexes reveals a cluster of ~6-nm filaments, suspected to represent the connector, between the basal bodies and nuclei.A mutant with a variable number of flagella, vfl-2-220, is defective with respect to the nucleus-basal body association. This observation encourages us to speculate that the nucleusbasal body union is important for accurate basal body localization within the cell and/or for accurate segregation of parental and daughter basal bodies at cell division.A physical association between nuclei and basal bodies or centrioles has been observed in a variety of algal, protozoan, and metazoan cells, although the nature of the association, in terms of both structure and function, has been obscure. We believe it likely that fibrous connectors homologous to those described here for Chlamydomonas are general features of centriole-bearing eucaryotic cells.The basal body cycle of Chlamydomonas resembles the classical centriole cycle in most, if not all, essential respects, and so an analysis of the Chlamydomonas basal body cycle may provide information about centriole cycles in general. The cytological behavior of centrioles during the cell cycle is well known (43). Landmark events in the centriole cycle include duplication during interphase, migration to the nuclear poles before mitosis, presence at the mitotic spindle poles, and equal segregation to daughter cells at division. Despite a very large body of literature on centriole structure and cytology, the cellular function of centrioles remains obscure, and most of the questions raised when centrioles were observed more than one hundred years ago remain unanswered. Why are centrioles maintained in such a wide variety of organisms? How do centriole duplication and segregation occur? Is proper subcellular localization of centrioles important to their function?Protozoan centrioles are generally referred to as basal bodies, and we will follow this convention throughout this paper. But the reader should bear in mind that in many cell types, both metazoan and protozoan, a basal body or centri...

Coordinated beating of algal flagella is mediated by basal coupling

“…The DF contains centrin, also found in nuclear basal body connectors (NBBCs) (Fig. 1B), which are involved in localization of BBs during cell division (37). The two BBs have an identical structure of nine triplet microtubules that form a cartwheel arrangement (38).…”

“…In CR, robust NBBCs descending near the DF link BBs to the nucleus (Fig. 1B), and remain intact even after detergent lysis treatment (37). These can be induced by calcium to undergo significant contraction (69).…”

Common themes in centriole and centrosome movements

“…RNAi ablation of tubulin does not prevent 118 polarity establishment and is not required for centriole-cortex interaction [7,29], suggesting 119 that another cytoskeletal polymer mediates centriole position. However, another study found 120 that tubulin disruption delays polarity induction, which requires a small centrosomal 121 microtubule aster [30]; therefore the precise role of microtubules in this process remains to be 122 by centrin-containing rhizoplasts [61]. Is the nucleus, the centriole or both involved in the 209 movement to and from the apical surface?…”

The Uni2 Phosphoprotein is a Cell Cycle–regulated Component of the Basal Body Maturation Pathway inChlamydomonas reinhardtii

“…Additional centrin-containing fibers descend from the basal bodies toward the nucleus ending in fimbrae that drape around the nucleus. NFAps were obtained by lysis of whole cells with nonionic detergent (Wright et al, 1985). A DIC image of the NFAp depicted in Figure 6H shows a successful extraction of cytoplasmic components.…”

“…Indirect immunofluorescence in whole cells and nucleoflagellar apparatuses (NFAps) was conducted as described by Silflow et al (2001) based on methods described in Sanders and Salisbury (1995) and Wright et al (1985) with the following modifications. The rat anti-HA (3F10) high-affinity antibody (Roche Molecular Biochemical) was used at a 1:200 dilution and detected using a 488-conjugated goat anti-rat secondary antibody (Sigma Aldrich) at a 1:400 dilution.…”