Abstract
Establishing left–right asymmetry is a fundamental process essential for arrangement of visceral organs during development. In vertebrates, motile cilia-driven fluid flow in the left–right organizer (LRO) is essential for initiating symmetry breaking event. Here, we report that myosin 1d (myo1d) is essential for establishing left–right asymmetry in zebrafish. Using super-resolution microscopy, we show that the zebrafish LRO, Kupffer’s vesicle (KV), fails to form a spherical lumen and establish proper unidirectional flow in the absence of myo1d. This process requires directed vacuolar trafficking in KV epithelial cells. Interestingly, the vacuole transporting function of zebrafish Myo1d can be substituted by myosin1C derived from an ancient eukaryote, Acanthamoeba castellanii, where it regulates the transport of contractile vacuoles. Our findings reveal an evolutionary conserved role for an unconventional myosin in vacuole trafficking, lumen formation, and determining laterality.
Highlights
Establishing left–right asymmetry is a fundamental process essential for arrangement of visceral organs during development
We found a significantly higher number of fragmented nuclei in myo1d MZ embryos compared to wild type at 1S and 6S stage (Fig. 4a, b), suggesting that accumulation of vacuoles may cause Kupffer’s vesicle (KV) epithelial cells to burst that may account for the lower cell number (Supplementary Fig. 4d, e)
In zebrafish, myo1d provides the forces required for vacuole delivery and generation of AP cell shape rearrangement of KV
Summary
Establishing left–right asymmetry is a fundamental process essential for arrangement of visceral organs during development. Motile cilia-driven fluid flow in the left–right organizer (LRO) is essential for initiating symmetry breaking event. Using super-resolution microscopy, we show that the zebrafish LRO, Kupffer’s vesicle (KV), fails to form a spherical lumen and establish proper unidirectional flow in the absence of myo1d. This process requires directed vacuolar trafficking in KV epithelial cells. KV lumen formation is a cord hollowing process[16] and its threshold size is critical for creating a unidirectional flow and consistent laterality[6]. Vacuolar trafficking by Myo1d and expulsion of intracellular fluid from KV epithelial cells into the lumen is essential for attaining definitive spherical shape and threshold lumen size that specifies embryo laterality
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