Microtubule organization in cell proliferation and differentiation

How are centrosomes and cilia assembled and how do they function?

The centrosome is composed of a pair of centrioles, surrounded by a proteinaceous pericentriolar material (PCM). The PCM harbors the microtubule nucleating activity, which at least in part depends on the γ-tubulin ring complex (γTuRC) and is crucial for the centrosome to function as MTOC. We aim to understand how γTuRC is recruited to centrioles and how recruitment is coupled to γTuRC activation, to convert centrioles into MTOCs.

Apart from functioning as MTOCs, centrioles are essential for the formation and function of cilia. We are interested in how MTOC function is coordinated with cilium assembly and disassembly both during the cell cycle and during cell differentiation.

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How is the microtubule cytoskeleton organized in non-transformed cells and how is it remodeled during their differentiation?

Most of our molecular understanding regarding the structures and mechanisms that constitute and organize the microtubule cytoskeleton was obtained through functional studies in transformed cancer cell lines. However, recent work suggests that non-transformed cells implicated in normal development as well as numerous diseases may employ different or additional, yet-to-be-discovered mechanisms to organize their microtubule networks. To close this knowledge gap, we characterize the roles of known MTOCs such as the centrosome and of novel, non-centrosomal MTOCs in human iPSCs and derived cell types during tissue formation.

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How does the microtubule nucleator γ-tubulin ring complex (γTuRC) nucleate microtubules and how is it regulated?

An important question is how cells control the formation of new microtubules, which is crucial for assembly and remodeling of microtubule arrays. Microtubule formation does not occur spontaneously, but requires a nucleator such as γTuRC. γTuRC was proposed to provide a template for the assembly of new microtubules. A major recent advance contributed by our lab was the in vitro reconstitution of human γTuRC, which now allows a detailed structure-function analysis of the nucleation mechanism and of its regulation. Cryo-EM analyses of purified γTuRC have revealed a surprising asymmetry that is incompatible with the template nucleation model. How γTuRC gets activated to become an efficient nucleation template is a major open question.

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How do defects in the microtubule cytoskeleton cause disease?

Mutations in genes encoding proteins that constitute or regulate centrosomes are associated with impaired developmental growth, in particular during brain development, resulting in microcephaly (reduced brain size). Defective formation or function of cilia has been linked to disorders collectively known as ciliopathies, which affect the development and function of a wide range of body parts and organs. We aim to use insight generated in our analyses of fundamental, microtubule cytoskeleton-related processes to unravel the molecular and cellular causes of associated diseases.

A recent example is Cohen Syndrome, a rare developmental disorder, characterized by a range of clinical features including developmental delay, microcephaly, intellectual disability, obesity, low muscle tone, neutropenia (a reduction in immune cells that fight infections), and progressive retinopathy (loss of vision). Unfortunately, due to limited awareness and funding opportunities, many rare diseases including Cohen Syndrome are understudied and there are no or only limited treatment options. Thus, basic research elucidating the underlying molecular and cellular causes is urgently needed. Since we suspect an involvement of the microtubule cytoskeleton in Cohen Syndrome, we leverage our expertise in this area and work with patient families (through the Spanish Cohen Syndrome Association SICOES) (https://www.facebook.com/profile.php?id=100076486994683), and treating clinicians, to establish cell and tissue models to study the disease.

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