Abstract
Mouse embryo imaging is conventionally carried out on ex vivo embryos excised from the amniotic sac, omitting vital structures and abnormalities external to the body. Here, we present an in amnio MR imaging methodology in which the mouse embryo is retained in the amniotic sac and demonstrate how important embryonic structures can be visualised in 3D with high spatial resolution (100 µm/px). To illustrate the utility of in amnio imaging, we subsequently apply the technique to examine abnormal mouse embryos with abdominal wall defects. Mouse embryos at E17.5 were imaged and compared, including three normal phenotype embryos, an abnormal embryo with a clear exomphalos defect, and one with a suspected gastroschisis phenotype. Embryos were excised from the mother ensuring the amnion remained intact and stereo microscopy was performed. Embryos were next embedded in agarose for 3D, high resolution MRI on a 9.4T scanner. Identification of the abnormal embryo phenotypes was not possible using stereo microscopy or conventional ex vivo MRI. Using in amnio MRI, we determined that the abnormal embryos had an exomphalos phenotype with varying severities. In amnio MRI is ideally suited to investigate the complex relationship between embryo and amnion, together with screening for other abnormalities located outside of the mouse embryo, providing a valuable complement to histology and existing imaging methods available to the phenotyping community.
Highlights
Mice are widely used as research models for investigating development and disease as the murine genome can be readily manipulated to create phenotypes analogous to human conditions
Ex vivo mouse embryo Magnetic resonance imaging (MRI) is carried out on mid to late gestation embryos, which have been extracted from the mother, removed from the amniotic sac and exsanguinated by cutting the umbilical cord close to the abdomen [10]
We describe a new in amnio MR imaging method in which the mouse embryo is retained within the amniotic sac, complementing the existing ex vivo embryo screening protocol by providing additional information on the developmental relationship between the embryo, fine external structures, umbilical cord and placenta
Summary
Mice are widely used as research models for investigating development and disease as the murine genome can be readily manipulated to create phenotypes analogous to human conditions. Ex vivo mouse embryo MRI is carried out on mid to late gestation embryos (typically aged between E14.5 and 18.5), which have been extracted from the mother, removed from the amniotic sac and exsanguinated by cutting the umbilical cord close to the abdomen [10]. Whilst this protocol is sufficient for screening the majority of abnormal embryos, abnormalities associated with the amnion, the placenta or external structures that are fine or damaged could be missed. These include placental defects, such as preeclampsia [11] and intrauterine growth retardation [12], as well as abdominal wall abnormalities, such as exomphalos and gastroschisis, in which the defect may not be accurately delineated due to disruption of structures whilst extracting and preparing the embryo [13]
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