ABSTRACT Dense populations of Urceolaria mitra (Cilophora, Peritrichid) were observed on the surface of the planarian Polycelis tenuis (Platyhelminthes Turbellaria). Although the epizoite was primarily confined to the anterior dorsal surface of the planarian, heavily infested individuals had peritrichs attached to the posterior, lateral and ciliated ventral surfaces. Unique profiles of the skeletal ring (aboral disc) in relation to the host surface showed that some local erosion of planarian epithelium occurs. Outer and inner rows of cilia extended anti‐clockwise around the peristomal disc. The cilia ran for one and one‐eighth turns around the disc and overlapped in the form of a spiral when the protist was extended and feeding. The cilia appeared to beat in metachronal rhythm and exhibited a wavelength and amplitude of approximately 10μm. Regular striations having a periodicity of 1μm were observed in the periostimal membrane. A posterior or basal circlet of locomotor cilia was also observed and freeze fracture revealed an internal arrangement of microvilli, cilia and reticular membranes.
1. 1. Da Silva-Buttkus P., 2. et al.
2008. J. Cell Sci. doi:10.1242/jcs.036400
[OpenUrl][1][Abstract/FREE Full Text][2]
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In the ovary, initiation of follicle growth is marked by cuboidalization of flattened granulosa cells (GCs). The regulation and cell biology of this shape change remains poorly understood. We propose that characterization of intercellular junctions and associated proteins is key to identifying as yet unknown regulators of this important transition. As GCs are conventionally described as epithelial cells, this study used mouse ovaries and isolated follicles to investigate epithelial junctional complexes (tight junctions [TJ], adherens junctions [AJ], and desmosomes) and associated molecules, as well as classic epithelial markers, by quantitative PCR and immunofluorescence. These junctions were further characterized using ultrastructural, calcium depletion and biotin tracer studies. Junctions observed by transmission electron microscopy between GCs and between GCs and oocyte were identified as AJs by expression of N-cadherin and nectin 2 and by the lack of TJ and desmosome-associated proteins. Follicles were also permeable to biotin, confirming a lack of functional TJs. Surprisingly, GCs lacked all epithelial markers analyzed, including E-cadherin, cytokeratin 8, and zonula occludens (ZO)-1alpha+. Furthermore, vimentin was expressed by GCs, suggesting a more mesenchymal phenotype. Under calcium-free conditions, small follicles maintained oocyte-GC contact, confirming the importance of calcium-independent nectin at this stage. However, in primary and multilayered follicles, lack of calcium resulted in loss of contact between GCs and oocyte, showing that nectin alone cannot maintain attachment between these two cell types. Lack of classic markers suggests that GCs are not epithelial. Identification of AJs during GC cuboidalization highlights the importance of AJs in regulating initiation of follicle growth.
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