Structural insights into the architecture and assembly of eukaryotic flagella

Abstract

Cilia and flagella are slender projections found on most eukaryotic cells including unicellular organisms such as Chlamydomonas, Trypanosoma and Tetrahymena, where they serve motility and signaling functions. The cilium is a large molecular machine consisting of hundreds of different proteins that are trafficked into the organelle to organize a repetitive microtubule-based axoneme. Several recent studies took advantage of improved cryo-EM methodology to unravel the high-resolution structures of ciliary complexes. These include the recently reported purification and structure determination of axonemal doublet microtubules from the green algae Chlamydomonas reinhardtii, which allows for the modeling of more than 30 associated protein factors to provide deep molecular insight into the architecture and repetitive nature of doublet microtubules. In addition, we will review several recent contributions that dissect the structure and function of ciliary trafficking complexes that ferry structural and signaling components between the cell body and the cilium organelle.

Evidence for intraflagellar transport in butterfly spermatocyte cilia

“…We examined the cilia in spermatocytes in Pieris brassicae , also known as the cabbage butterfly or large white butterfly, a common agricultural pest native to Europe, Asia, and north Africa. While our analysis confirmed that P. brassicae spermatocytes have long cilia that persist in meiotic division, we also found that they contain thin filamentous structures of electron dense material at the base of the CLRs and along the ciliary membrane of the elongating CLRs that appear to be analogous to the IFT trains first observed in Chlamydomonas (Petriman and Lorentzen, 2020; Scholey, 2003). The findings reported here for P. brassicae provide new insights into a potential role for IFT in insect spermatocytes and opens new questions about differential involvement of IFTs in Drosophila spermatogenesis versus other systems.…”

“…While our analysis confirmed that P. brassicae spermatocytes have long cilia that persist in meiotic division, we also found that they contain thin filamentous structures of electron dense material at the base of the CLRs and along the ciliary membrane of the elongating CLRs that appear to be analogous to the IFT trains first observed in Chlamydomonas (Petriman and Lorentzen, 2020;Scholey, 2003).…”

“…Cilia are organelles that project from the cell surface with key functions in physiology and development that occur widely in eukaryotes from protists to mammals (Berbari et al, 2009; Bloodgood, 2009; Buchwalter et al, 2016; Fisch and Dupuis-Williams, 2011; Gerdes et al, 2009; Ishikawa and Marshall, 2011; Jana et al, 2016; Petriman and Lorentzen, 2020; Santos and Reiter, 2008; Singla and Reiter, 2006; Vincensini et al, 2011). They are critical organelles for signal transduction and transmit sensory input from a variety of environmental and interorgan signals.…”

Primary Cilia: A Cellular Regulator of Articular Cartilage Degeneration

“…The transition zone, an intermediate region between the basal body and the axoneme, consists of transition fibers and Y-links, which act as a ciliary gate, controlling soluble proteins and selected components in and out of cilia [19][20][21]. Here, the nine microtubules of the basal body are transformed from triplets into doublets, which form the backbone of the ciliary axoneme (known as the 9 + 0 arrangement, it lacks one pair of central microtubules and dynein arms, which is different from motor cilia) [22]. In addition, the axoneme is covered with a ciliary membrane that extends to the plasma membrane, but has different components.…”

Evidence for intraflagellar transport in butterfly spermatocyte cilia

“…Cilia are organelles that project from the cell surface with key functions in physiology and development that occur widely in eukaryotes from protists to mammals (Berbari, O'Connor, Haycraft, & Yoder, 2009; Bloodgood, 2009; Buchwalter, Chen, Zheng, & Megraw, 2016; Fisch & Dupuis‐Williams, 2011; Gerdes, Davis, & Katsanis, 2009; Ishikawa & Marshall, 2011; Jana, Bettencourt‐Dias, Durand, & Megraw, 2016; Petriman & Lorentzen, 2020; Santos & Reiter, 2008; Singla & Reiter, 2006; Vincensini, Blisnick, & Bastin, 2011). They are critical organelles for signal transduction and transmit sensory input from a variety of environmental and interorgan signals.…”