Basal bodies across eukaryotes series: basal bodies in the freshwater planarian Schmidtea mediterranea

Abstract

The freshwater planarian Schmidtea mediterranea has recently emerged as a valuable model system to study basal bodies (BBs) and cilia. Planarians are free-living flatworms that use cilia beating at the surface of their ventral epidermis for gliding along substrates. The ventral epidermis is composed of multiciliated cells (MCCs) that are similar to the MCCs in the respiratory airways, the brain ventricles, and the oviducts in vertebrates. In the planarian epidermis, each cell assembles approximately eighty cilia that beat in a coordinate fashion across the tissue. The BBs that nucleate these cilia all assemble de novo during terminal differentiation of MCCs. The genome of the planarian S. mediterranea has been sequenced and efficient methods for targeting gene expression by RNA interference are available. Defects induced by perturbing the expression of BB proteins can be detected simply by analyzing the locomotion of planarians. BBs are present in large numbers and in predictable orientation, which greatly facilitates analyses by immunofluorescence and electron microscopy. The great ease in targeting gene expression and analyzing associated defects allowed to identify a set of proteins required for BB assembly and function in planarian MCCs. Future technological developments, including methods for transgenic expression in planarians and in related species, will achieve turning free-living flatworms into powerful model systems to study MCCs and the associated human pathologies.

CCDC61/VFL3 Is a Paralog of SAS6 and Promotes Ciliary Functions

“…A specific role of CCDC61 in the anchoring of basal bodies in multiciliated cells is also suggested by experiments in the planarian S. mediterranea. Planaria move by gliding on a ventral array of multiciliated cells (Azimzadeh and Basquin, 2016). Knockdown of CCDC61 in S. mediterranea was found to result in an abnormal direction of locomotion (Azimzadeh et al, 2012) due to basal body mis-orientations caused by a failure to generate basal feet and ciliary rootlets correctly (Basquin et al, 2019).…”

Centrosomal and Non-Centrosomal Microtubule-Organizing Centers (MTOCs) in Drosophila melanogaster

“…The ability to successfully accomplish cell division without centrosomes is not unique to Drosophila , however. Cell division in some planarians [ 112 ] and plants [ 113 ], as well as oocyte meiosis in the majority of animal species [ 114 , 115 , 116 , 117 ], routinely occurs without centrosomes [ 1 ]. Although centrosomes provide the dominant mechanism for MT organization into a bipolar spindle in Xenopus extracts, they are not required for spindle assembly as MTs are organized around mitotic chromatin when centrosomes are absent [ 116 ].…”

A dynamically diluted alignment model reveals the impact of cell turnover on the plasticity of tissue polarity patterns

“…The regeneration of a second head instead of a tail (figure 1a-c) can be assumed to constitute a conflicting cue for the polarization pattern in preexisting tissues. The multi-ciliated ventral epithelium is likely to be one such planarly polarized tissue [29,30]. Its cilia drive the gliding locomotion of planarians, implying consistent polarization of individual cilia and thus of the ventral epithelium as a whole [31,32].…”