The Biology of Motile Cilia

Cilia are microtubule-based cellular extensions that play key roles in sensing the extracellular environment, processing developmental signals and generating propulsive force and fluid flow. They also act as secretory organelles releasing bioactive vesicular ectosomes involved in cell-cell communication and other processes.

Cilia are ancient and complex; in humans, ~5% of all genes are involved in their formation/activity and defects result in complex syndromes or ciliopathies. For many years, my laboratory has been broadly interested in the assembly and function of motile cilia, and has a strong record of identifying new opportunities and pursuing them

to reveal novel aspects of ciliary biology – most recently we demonstrated that cilia act as a source of peptidergic signals. For most studies, we utilize the biciliate unicellular green alga Chlamydomonas as a model due to the ease of biochemical analysis and large array of molecular genetic approaches available. Over the next five

years, we will pursue two broad areas of focus to address what I consider key questions in ciliary biology. Although superficially distinct, these two areas are intimately connected, and I anticipate we will be able to integrate them to yield novel insights into conserved and essential cilia-based pathways.

1) Ciliary Motility: dissecting the dynein motors and control systems that generate ciliary beating and power retrograde intraflagellar transport (IFT). We plan to focus on three major issues. We will dissect the complex pathways by which axonemal and IFT dyneins are synthesized and assembled in cytoplasm employing our

newly devised biochemical fractionation methods. Building a cilium is an immensely complex problem in macromolecular assembly and we will examine how assembly factors control the axonemal incorporation of outer dynein arms at precise locations on doublet microtubules. We will also study axonemal dynein motor

regulation to a) determine how responses to alterations in Ca2+ and redox poise are combined with curvature sensing to yield integrated changes in motility, and b) assess how cells sense imposed changes in ciliary beating and respond by increasing intraciliary levels of the dynein regulator Lis1. 2) Cilia Formation and Peptidergic Signaling: studying the peptide amidating enzyme (peptidylglycine -

amidating monooxygenase; PAM) and its amidated bioactive products in ciliary assembly and cilia-based cell- cell communication. We recently demonstrated that active PAM occurs in cilia and that PAM loss leads to the failure of ciliogenesis and disrupts dynein-driven retrograde IFT. Furthermore, PAM-generated amidated

bioactive products are released in cilia-derived vesicular ectosomes and one acts as a chemotactic modulator. We will build on these observations to identify novel amidated PAM products involved in cilia formation. We will dissect the pathways leading to regulated amidated product release in ciliary ectosomes and determine

where/when processing of the precursors occurs. We will also pursue the amidated product receptors and their downstream signaling pathways, which lead to differential regulation of the two motile cilia and chemotaxis.