Intercellular and intracellular cilia orientation is coordinated by CELSR1 and CAMSAP3 in oviduct multi-ciliated cells.

The molecular mechanisms by which cilia orientation is coordinated within and between multi-ciliated cells (MCCs) are not fully understood. In the mouse oviduct, MCCs exhibit a characteristic basal body (BB) orientation and microtubule gradient along the tissue axis. The intracellular polarities were moderately maintained in cells lacking CELSR1 (cadherin EGF LAG seven-pass G-type receptor 1), a planar cell polarity (PCP) factor involved in tissue polarity regulation, although the intercellular coordination of the polarities was disrupted. However, CAMSAP3 (calmodulin-regulated spectrin-associated protein 3), a microtubule minus-end regulator, was found to be critical for determining the intracellular BB orientation. CAMSAP3 localized to the base of cilia in a polarized manner, and its mutation led to the disruption of intracellular coordination of BB orientation, as well as the assembly of microtubules interconnecting BBs, without affecting PCP factor localization. Thus, both CELSR1 and CAMSAP3 are responsible for BB orientation but in distinct ways; their cooperation should therefore be critical for generating functional multi-ciliated tissues.

Generation of pulsatile ERK activity in mouse embryonic stem cells is regulated by Raf activity.

The extracellular signal-regulated kinase (ERK) is a serine/threonine kinase that is known to regulate cellular events such as cell proliferation and differentiation. The ERK signaling pathway is activated by fibroblast growth factors, and is considered to be indispensable for the differentiation of primitive endoderm cells, not only in mouse preimplantation embryos, but also in embryonic stem cell (ESC) culture. To monitor ERK activity in living undifferentiated and differentiating ESCs, we established EKAREV-NLS-EB5 ESC lines that stably express EKAREV-NLS, a biosensor based on the principle of fluorescence resonance energy transfer. Using EKAREV-NLS-EB5, we found that ERK activity exhibited pulsatile dynamics. ESCs were classified into two groups: active cells showing high-frequency ERK pulses, and inactive cells demonstrating no detectable ERK pulses during live imaging. Pharmacological inhibition of major components in the ERK signaling pathway revealed that Raf plays an important role in determining the pattern of ERK pulses.

Coordination of Cilia Movements in Multi-Ciliated Cells.

Multiple motile cilia are formed at the apical surface of multi-ciliated cells in the epithelium of the oviduct or the fallopian tube, the trachea, and the ventricle of the brain. Those cilia beat unidirectionally along the tissue axis, and this provides a driving force for directed movements of ovulated oocytes, mucus, and cerebrospinal fluid in each of these organs. Furthermore, cilia movements show temporal coordination between neighboring cilia. To establish such coordination of cilia movements, cilia need to sense and respond to various cues, including the organ's orientation and movements of neighboring cilia. In this review, we discuss the mechanisms by which cilia movements of multi-ciliated cells are coordinated, focusing on planar cell polarity and the cytoskeleton, and highlight open questions for future research.