Following our latest data release, the DMDD website (dmdd.org.uk) now contains detailed phenotype data for nearly 700 embryos from 82 different knockout mouse lines. Highlights include the identification of limb defects and cysts in Col4a2 knockouts and replication of the major features of Meckel syndrome in B9d2 knockouts.
We have begun to add immunohistochemistry image data for the brain and spinal cord of some embryos at E18.5. These images give further information about lines in which the embryos appeared morphologically normal at E14.5, but were still not viable. We have also added viability data for every line at both E9.5 and E14.5.
Together with the placental phenotype data that we hold for more than 100 knockout lines, the DMDD website is a rich resource for those investigating the effect of gene mutations on embryo development, and may provide clues about the genetic basis of rare diseases.
LIMB DEFECTS SEEN IN Col4a2 KNOCKOUTS
In humans, COL4A2 mutations have been linked to porencephaly, a rare disorder with phenotypes that include the development of intracranial cysts. In the latest DMDD data, Col4a2 knockouts have a variety of nervous system disorders in line with porencephaly. However, all four embryos also show abnormal autopod morphology and cysts between the nasal septum and the oral cavity, as well as other morphological defects.
B9d2 KNOCKOUTS MODEL MECKEL SYNDROME
In humans, mutations of the gene B9D2 have been linked to Meckel syndrome, a severe disorder caused by dysfunction of the primary cilia during the early stages of embryogenesis. Meckel syndrome is characterised by multiple kidney cysts, occipital encephalocele (where a portion of the brain protrudes through an opening in the skull) and polydactyly, but it also commonly affects the brain and spinal cord, eyes, heart, lungs and bones.
B9d2 knockout mouse embryos included in our latest data release show the major features of Meckel syndrome, including polydactyly and defects in the brain, peripheral nervous system, heart and vascular system. They also display situs defects, where the left-right asymmetry of the body did not develop as expected. The image below shows a B9d2 knockout embryo with left pulmonary isomerism and symmetric branching of the principle bronchi from the trachea.
NEURAL IMAGE DATA NOW AVAILABLE
In around 20% of embryonic lethal lines, embryos appear morphologically normal at E14.5 but still go on to die before or shortly after birth. To understand more about why these embryos were not viable, DMDD colleagues Professor Corinne Houart and Dr Ihssane Bouybayoune at Kings College London analysed the lines at E18.5 – when embryo development is almost complete. They used immunohistochemistry to identify abnormalities in the brain and spinal cord that could not be picked up in our standard, whole-embryo morphological analyses. This data is now available for the line Trappc9, and additional lines will be added in future data releases.
Neural images are available as 20-micron sections through the brain and spinal cord, and the images from different embryos can be compared side by side using the stack viewer. A separate Nissl stain was used to highlight neural death and these images can also be explored online.