High-resolution contrast-enhanced microCT reveals the true three-dimensional morphology of the murine placenta


Photo : L’histologie virtuelle en 3D passe à la haute résolution à Louvain(s) (© Daily Science)

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Genetic engineering of the mouse genome identified many genes that are essential for embryogenesis. Remarkably, the prevalence of concomitant placental defects in embryonic lethal mutants is highly underestimated and indicates the importance of detailed placental analysis when phenotyping new individual gene knockouts. Here, we introduce high-resolution contrast-enhanced microfocus computed tomography (CE-CT) as a non-destructive, high throughput technique to evaluate the 3D placental morphology. Using a novel contrast agent, Zirconium-substituted Keggin polyoxometalate (Zr-POM), the soft tissue of the placenta (i.e. different layers and cell types, and its vasculature) was imaged with a resolution of 3.5μm voxel size. This novel approach allowed us to visualize and study early and late stages of placental development. Moreover, CE-CT provides a method to precisely quantify placental parameters (i.e. volumes, volume fraction, ratio of different placental layers and volumes of specific cell populations) that are crucial for statistical comparison studies. The CE-CT assessment of the 3D morphology of the placentas was validated (i) by comparison to standard histological studies, (ii) by evaluating placentas from two different mouse strains, 129S and C57BL/6J mice and (iii) by confirming the placental phenotype of mice lacking phosphoinositol 3-kinase (PI3K)-p110α. Finally, the Zr-POM-based CE-CT allowed for inspection of the vasculature structure in the entire placenta, as well as detecting placental defects in pathologies characterised by embryonic resorption and placental fusion. Taken together, Zr-POM-based CE-CT offers a novel quantitative 3D methodology to investigate placental development or pathologies.

Prof. Greet KerckhofsOur paper (see https://www.pnas.org/content/early/2019/06/25/1902688116) describes an innovative 3D imaging technique that allows, non-invasively, to visualize biological tissues, to characterize their 3D microstructure and to analyse spatial relationships between tissues. We call this technique "virtual 3D histology". The imaging methodology (stains, imaging protocol, image analysis) has been developed by the research group of Prof. G. Kerckhofs (UCLouvain). Using this novel imaging methodology, it was possible to study very early stages of embryonic development in an intact mouse uterus. Moreover, this new technique offers the possibility to study the development of the placenta in 3D at an unprecedented spatial resolution during pregnancy. In this way, it is possible to dissect different placental compartments and to quantify them correctly in intact placental tissue. As a direct outcome, this study will enable new insights to be gained in the future in certain placental pathologies such as mono- and dichorionic twin placentas and placental infarctions.
Within the current study, the focus was on placental tissue and embryonic development. However, our novel imaging methodology, i.e. virtual 3D histology, has many more potential applications. Indeed, it will show strong added value for complex and highly heterogeneous biological tissues, such as cardiovascular tissues (arteries, heart valves and heart tissue), lungs, kidneys, and many more.
Finally, we would like to highlight that our study is an important example of the strength of interdisciplinary work. Indeed, the collaborative effort between engineers (group of Prof. Kerckhofs) and biomedical scientists (Prof. J. Vriens) was crucial in order to come up with this novel methodology. In addition, the study also highlights the strong collaboration between the KU Leuven (Professor Vriens’ group) and UCLouvain (Prof. Kerckhofs’ group).


Published on July 05, 2019