Xenopus as a model for studies in mechanical stress and cell division

Abstract

We exist in a physical world, and cells within biological tissues must respond appropriately to both environmental forces and forces generated within the tissue to ensure normal development and homeostasis. Cell division is required for normal tissue growth and maintenance, but both the direction and rate of cell division must be tightly controlled to avoid diseases of over-proliferation such as cancer. Recent studies have shown that mechanical cues can cause mitotic entry and orient the mitotic spindle, suggesting that physical force could play a role in patterning tissue growth. However, to fully understand how mechanics guides cells in vivo, it is necessary to assess the interaction of mechanical strain and cell division in a whole tissue context. In this mini-review we first summarise the body of work linking mechanics and cell division, before looking at the advantages that the Xenopus embryo can offer as a model organism for understanding: (1) the mechanical environment during embryogenesis, and (2) factors important for cell division. Finally, we introduce a novel method for applying a reproducible strain to Xenopus embryonic tissue and assessing subsequent cell divisions.

Keywords: Xenopus laevis; biomechanics; division orientation; mitosis.

Figure 1. Method to simultaneously apply a reproducible strain and analyse cell division in the Xenopus animal cap

a) The animal cap is dissected (red lines) from an early gastrula stage embryo that has been labeled by injection of GFP-α-tubulin and Cherry-histone2B mRNAs at the 2 cell stage. The dark brown area indicates the pigmented apical cell layer that will be imaged. b) Animal caps are cultured on a fibronectin coated flexible PDMS membrane until adhered. The PDMS membrane is cast in a custom mould with teeth on all four sides allowing either a uni-axial or biaxial stretch to be applied. c) PDMS membrane with cultured animal caps (arrow) attached to stretch apparatus. A uniaxial stretch is applied to stretch the animal caps by 35%; the teeth orthogonal to the stretch direction have been removed. d) The stretch apparatus is attached to the stage of an upright confocal microscope; a water-dipping objective is used to visualize cells in the apical layer. e) Example timelapse series using maximum intensity projections of cell division in the apical cell layer with frames 5 minutes apart. 35% stretch was applied in horizontal direction. The dividing cell is marked by dashed outline at 0 min, GFP-α-tubulin (green) labels the microtubule cytoskeleton and condensing centrosomes (arrowheads), Cherry-histone2B (magenta) labels nuclei. Scale bar: 30μm.