BLD10/CEP135 Is a Microtubule-Associated Protein that Controls the Formation of the Flagellum Central Microtubule Pair

Abstract

Cilia and flagella are involved in a variety of processes and human diseases, including ciliopathies and sterility. Their motility is often controlled by a central microtubule (MT) pair localized within the ciliary MT-based skeleton, the axoneme. We characterized the formation of the motility apparatus in detail in Drosophila spermatogenesis. We show that assembly of the central MT pair starts prior to the meiotic divisions, with nucleation of a singlet MT within the basal body of a small cilium, and that the second MT of the pair only assembles much later, upon flagella formation. BLD10/CEP135, a conserved player in centriole and flagella biogenesis, can bind and stabilize MTs and is required for the early steps of central MT pair formation. This work describes a genetically tractable system to study motile cilia formation and provides an explanation for BLD10/CEP135's role in assembling highly stable MT-based structures, such as motile axonemes and centrioles.

Small organelle, big responsibility: the role of centrosomes in development and disease

“…Both ORC1 and pericentrin mutant cells show defective ciliary recruitment of the Shh receptor, Smoothened and consequently abnormal Shh signalling with potentially wide-ranging effects on development [107]. As the primary cilium assembles on a basal body, a structure derived from the mother centriole, CEP152 and CPAP, along with the MCPH proteins, STIL and CEP135, are required not only for centriole biogenesis but also for ciliogenesis [108][109][110][111][112]. Given the link between centriole biogenesis and primary cilia assembly, it is puzzling that patients carrying MCPHor PD-associated mutations in these essential regulators do not exhibit clinical signs of defective ciliary function.…”

Methods to Study Centrosomes and Cilia in Drosophila

“…In spermatocytes and sperm cells, these organelles can be labeled using PACT::GFP (marks centrioles) and acetylated tubulin (marks centrioles and cilia) ( Figure 4C; for a detailed list of markers used in sperm cells see Table 1). The protocols mentioned here can be used to analyze centrioles and cilia in the mutants that affect the assembly, conversion and stability of these organelles [22]. However, to better understand the morphogenesis and functional transformations of these organelles in sperm cells it would be desirable to develop protocols for live imaging of centrosomes and cilia during spermatogenesis.…”

“…Thus, many of the centriole and cilium substructures are under the resolution limit of the light microscope, so a detailed ultrastructural analysis is critical to understand their mechanisms of assembly and maintenance. Although, the protocol to study centrosomes and cilia ultrastructure using transmission electron microscopy in embryo and larvae is not yet well established, these organelles have been investigated by several groups in the pupal/adult antenna and testes [15,20,22] (also see section 3.3).…”

“…As a result, in each early spermatid a single basal body (or centriole) nucleates the sperm flagellum. Interestingly, the elongating sperm flagellum that is motile consists of nine radially arranged doublet microtubules and a central pair of singlet microtubules (9+2) [22,23]. However, how immotile cilia and motile flagella are assembled and how different types of cilia grow from same basal body is still unclear.…”

“…For example, centrioles in the embryo are short and made of nine doublet microtubules, whereas those in sperm cells are uniquely long and consist of nine triplet microtubules (Figure 4,6) [27]. Long centrioles in sperm allow rapid and easy analysis of this organelle by imaging, providing an appropriate system to understand the mechanisms underlying centriole elongation [22,28]. Studies in centriolar cells with or without cilia in the embryo are widely appreciated [28].…”