Pleuralins are involved in theca differentiation in the diatom Cylindrotheca fusiformis

Diatom cells are encased within a silica-based cell wall (frustule) that se rves as armour-like protection for the enclosed protoplast. Maintaining the integrity of the frustule requires a precise coupling between the biogenes is of new frustule components and the cell cycle. Thus far, the molecular m echanisms by which this coupling is achieved are unknown. This study demons trates that pleuralins (formerly HEPs), a previously characterized family o f diatom cell wall proteins, are involved in cell cycle-dependent frustule development, The frustule is made up of two, overlapping half-shells termed the epitheca and hypotheca. Both thecae are morphologically identical, yet immunolocalisation with anti-pleuralin antibodies demonstrates that their protein composition is clearly different. During interphase, pleuralins are associated only with the epitheca, where they are confined to the inner su rface of the terminal elements (pleural bands) in the region of overlap wit h the hypotheca. At cell division, pleuralins also become associated with t he newly formed pleural bands of the hypotheca, Remarkably, this process is concomitant with the functional conversion of the parental hypotheca into the epitheca of one of the progeny cells. These results indicate that devel opmentally controlled association of pleuralins with the frustule is involv ed in hypotheca-epitheca differentiation, which is a crucial process to ens ure proper frustule development.