Furthermore, direct volumetric measurement of individual structures is facile

using modern 3D visualisation software packages (such as Amira [www.amiravis.com] and Osirix [www.osirix-viewer.com]) and is only limited by the task of selecting the desired region of interest. This opens the possibility of a more systematic and quantitative analysis of the changes in heart structure and composition during embryonic development. Not only would this resolve the extent of variation that may be inherent between individual embryos and the different mouse strains used in biomedical research, it may also provide an objective baseline for identifying developmental abnormalities Proteasome inhibitor that may be difficult to assess by qualitative criteria alone. For example, the normal range of variation in ventricular trabeculation is currently unknown. Grossly abnormal patterns have been identified in a few mutant mouse lines, which show embryonic lethality, but it is effectively impossible to identify milder phenotypes that might be helpful in analysing for example whether developmental aberrations underlie non-compaction disease. Similarly, HREM analysis has facilitated quantitative assessment of stenosis or dilation of the great intrathoracic arteries. Coarctation of the aorta or stenosis of the pharyngeal arch arteries and their see more derivatives often are associated with complex, intra-cardiac

and extra-cardiac defects [e.g.] [29, 30, 31, 32 and 33] which can result in prenatal or perinatal lethality. Accurate detection of stenosis in embryonic and foetal blood vessels requires histological sections cut precisely perpendicular

to the longitudinal axis of the artery being measured. Technically challenging with adult mice, this conventional approach is impossible with mouse embryos. Its digital equivalent is however straightforward with image volume data — and only HREM data PFKL currently provides spatial resolution adequate to yield meaningful measurements [34 and 35] (Figure 2). 3D modelling of gene expression patterns has had an important impact on our understanding of heart morphogenesis by revealing the contributions of different cell lineages either directly (using CRE-mediated recombination to activate reporter genes) or indirectly (using endogenous gene expression patterns as a surrogate for lineage marking). As more marker genes for cardiac cells and tissues are identified, such studies will increasingly allow all aspects of cardiac development to be reassessed. Gene expression studies have almost exclusively relied on staining individual sections, since this has yielded the most sensitive results and allowed investigation of several gene patterns simultaneously. However, as with studies of morphology, reconstruction of the expression data into 3D models inevitably results in significant loss of resolution, in part from the limited frequency of sections but also from the constraints imposed by poor section registration.