Whole population cell analysis of a landmark-rich mammalian epithelium reveals multiple elongation mechanisms

Abstract

Tissue elongation is a fundamental component of developing and regenerating systems. Although localised proliferation is an important mechanism for tissue elongation, potentially important contributions of other elongation mechanisms, specifically cell shape change, orientated cell division and cell rearrangement, are rarely considered or quantified, particularly in mammalian systems. Their quantification, together with proliferation, provides a rigorous framework for the analysis of elongation. The mammalian palatal epithelium is a landmark-rich tissue, marked by regularly spaced ridges (rugae), making it an excellent model in which to analyse the contributions of cellular processes to directional tissue growth. We captured confocal stacks of entire fixed mouse palate epithelia throughout the midgestation growth period, labelled with membrane, nuclear and cell proliferation markers and segmented all cells (up to ~20,000 per palate), allowing the quantification of cell shape and proliferation. Using the rugae as landmarks, these measures revealed that the socalled growth zone is a region of proliferation that is intermittently elevated at ruga initiation. The distribution of oriented cell division suggests that it is not a driver of tissue elongation, whereas cell shape analysis revealed that both elongation of cells leaving the growth zone and apico-basal cell rearrangements do contribute significantly to directional growth. Quantitative comparison of elongation processes indicated that proliferation contributes most to elongation at the growth zone, but cell shape change and rearrangement contribute as much as 40% of total elongation. We have demonstrated the utility of an approach to analysing the cellular mechanisms underlying tissue elongation in mammalian tissues. It should be broadly applied to higher-resolution analysis of links between genotypes and malformation phenotypes.

Mapping cellular processes in the mesenchyme during palatal development in the absence of Tbx1 reveals complex proliferation changes and perturbed cell packing and polarity

“…Unlike the previous analysis of proliferation in the secondary palate epithelium (Economou et al 2013), the proliferation index heat maps of palatal shelf mesenchyme showed a remarkably noisy and inconsistent pattern at all stages for both mutant and wild-type. Figure 3 shows illustrative examples for each stage, genotype and AP region.…”

“…Growth itself is typically not isotropic expansion by proliferation, but involves directional increase. It has previously been shown in palate epithelium that a significant proportion of the AP growth in that tissue is not proliferation-based, but rather arises by cell shape change and cell rearrangement (Economou et al 2013). In the present paper, a preliminary study has been described, as methods for capturing the separate components of directional growth in three dimensions and in mesenchyme are still in development.…”

Tissue tension and not interphase cell shape determines cell division orientation in the Drosophila follicular epithelium

“…The expansion and shaping of the Drosophila pupal notum and wing, and the mouse oral palate epithelium, are driven by the combined activity of cell division, rearrangement, shape changes, and cell extrusion (Economou et al, 2013;Guirao et al, 2015). Epithelial morphogenesis is a dynamic multiscale process that is the result of the coordination and integration of individual cell behaviors, including shape change, rearrangement, division, extrusion, and integration.…”

“…Developing tissues utilize different combinations of these cell behaviors in distinct biological contexts to drive morphogenesis. The expansion and shaping of the Drosophila pupal notum and wing, and the mouse oral palate epithelium, are driven by the combined activity of cell division, rearrangement, shape changes, and cell extrusion (Economou et al, 2013;Guirao et al, 2015). In contrast, salivary gland tube formation and germband extension in Drosophila embryos are driven by cell shape changes and cell rearrangements, with the latter process also including an additional small contribution from oriented cell divisions (reviewed in Ref.…”

Using cell deformation and motion to predict forces and collective behavior in morphogenesis

“…The first class focuses on the shape of cell outlines and their deformation [11, 12, 25, 27, 28]. For example, Blanchard et al define cell shape by fitting an ellipse to the cell outline (Figure 2A) [11].…”