Volumetric Dynamics of Lorica Forming Material Across the Cell Cycle in the Model Tintinnid Schmidingerella (Alveolata, Ciliophora)

Abstract

Background Tintinnids are marine planktonic ciliates with tube-shaped or vase-shaped loricae (shells). During cell division, lorica forming material (LFM) is generated and accumulates in the proter (anterior division product). After transverse fission, the proter leaves the lorica and secretes the material, creating its own shell, while the opisthe (posterior division product) retains the parental one. The timing of material production and its final quantity are unknown. Results Our study focuses on Schmidingerella Agatha & Strüder-Kypke, 2012, a model tintinnid genus with transparent, champagne flute-shaped loricae. We define five division stages based on the shapes of the opisthe’s newly forming membranellar zone (oral primordium), a feature recognisable both in live and fixed material. In monoclonal, methyl blue-eosin-stained culture material from the Northeast Pacific, the LFM is first perceptible in middle dividers and finally occupies on average 6.7% of the cell volume. The wall volume of the finished lorica estimated by a shape function is at least 4.5-fold larger than the volume of the intracellular material. Protargol-stained field material from the Chesapeake Bay at the Northwest Atlantic provides detailed morphometric data on morphostatic specimens (non-dividers) and dividers. Specimens from our culture and from the field material match in the timing of LFM production and its intracellular distribution. Conclusions The LFM is generated only during a certain period of the cell cycle, i.e., in early middle to late dividers. The LFM quantities in the different cell portions (anterior, middle, and posterior portion) suggest an increased production at the level of the oral primordium and the macronuclear nodules prior to its translocation into the anterior portion. The much larger volume of the finished lorica wall indicates a distinct swelling of the material after its secretion by the proter.