Defects in diffusion barrier function of ciliary transition zone caused by ciliopathy variations of TMEM218.

Primary cilia are antenna-like structures protruding from the surface of various eukaryotic cells, and have distinct protein compositions in their membranes. This distinct protein composition is maintained by the presence of the transition zone (TZ) at the ciliary base, which acts as a diffusion barrier between the ciliary and plasma membranes. Defects in cilia and the TZ are known to cause a group of disorders collectively called the ciliopathies, which demonstrate a broad spectrum of clinical features, such as perinatally lethal Meckel syndrome (MKS), relatively mild Joubert syndrome (JBTS), and nonsyndromic nephronophthisis (NPHP).

Formation of the B9-domain protein complex MKS1-B9D2-B9D1 is essential as a diffusion barrier for ciliary membrane proteins.

Cilia are plasma membrane protrusions that act as cellular antennae and propellers in eukaryotes. To achieve their sensory and motile functions, cilia maintain protein and lipid compositions that are distinct from those of the cell body. The transition zone (TZ) is a specialized region located at the ciliary base, which functions as a barrier separating the interior and exterior of cilia.

Spermatozoon of the freshwater rotifer Brachionus calyciflorus (Rotifera, Monogononta): Advances in morphological and ultrastructural studies.

The morphological and ultrastructural features of the spermatozoon in Brachionus calyciflorus are described using light, fluorescence and transmission electron microscopy (TEM). The mature spermatozoon, which appears to be thread-like, is composed of a slightly expanded anterior of cell body region and a flagellum region without acrosome. The cell body region and flagellum region are respectively 16-27μm and 20-33μm in length (n=60).