A landmark-free morphometric staging system for the mouse limb bud.

We have created a 2D morphometric analysis of the developing mouse hindlimb bud. This analysis has provided two useful resources for the study of limb development. First, a temporally accurate numerical description of shape changes during normal mouse limb development. Second, a web-based morphometric staging system, which has the advantage of being easy to use, and with a reproducibility of about ±2 hours. It allows users to upload a dorsal-view photo of a limb bud, draw a spline curve and thereby stage the bud within a couple of minutes. We describe how the system is constructed, its robustness to user variation and illustrate one application: the accurate tracking of spatiotemporal dynamics of gene expression patterns.