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Description
Chordocytes, in early zebrafish, pack in a small number of stereotyped patterns. Disruptions of the WT pattern are associated with developmental defects, including scoliosis. The dominant WT "staircase" pattern is the only regular pattern with transverse eccentricity. Morphometry and pattern analysis have established a length ratio governing which patterns will be observed. Physical models of cell packing in the notochord have established some relationships between geometric and mechanical ratios. Since a major function of the early notochord is to act as both a column and a beam, we aim to understand the overall resistance to compression and bending in terms of these mesoscale cell/tissue properties. To frame these relationships, we developed a model of the notochord as an elastic closed-cell foam, packed in either “staircase” or “bamboo” pattern. We determine the tension ratio between different surfaces in the notochord in terms of the relative stiffnesses and internal pressure. We determine the flexural rigidity of the model notochords in terms of relative stiffnesses and pressure. We find that the staircase pattern is more than twice as stiff as the bamboo pattern. The staircase pattern is also more than twice as stiff in lateral bending as in dorsoventral bending. This biomechanical difference may provide a specific developmental advantage to regulating the cell packing pattern in early-stage notochords.
