Quantitative Neuroanatomical Phenotyping of the Embryonic Mouse Brain.

Congenital neurodevelopmental anomalies are present from birth and are characterized by an abnormal development of one or more structures of the brain. Brain structural anomalies are highly comorbid with neurodevelopmental and neuropsychiatric disorders such as intellectual disability, autism spectrum disorders, epilepsy, and schizophrenia, and 80% are of genetic origin. We aim to address an important neurobiological question: How many genes regulate the normal anatomy of the brain during development. To do so, we developed a quantitative approach for the assessment of a total of 106 neuroanatomical parameters in mouse mutant embryos at embryonic day 18.5 across two planes commonly used in brain anatomical studies, the coronal and sagittal planes. In this article we describe the techniques we developed and explain why ultrastandardized procedures involving embryonic mouse brains are even more of prime importance for morphological phenotyping than adult mouse brains. We focus our analysis on brain size anomalies and on the most frequently altered brain regions including the cortex, corpus callosum, hippocampus, ventricles, caudate putamen, and cerebellum. Our protocols allow a standardized histology pipeline from embryonic mouse brain preparation to sectioning, staining, and scanning and neuroanatomical analyses at well-defined positions on the coronal and sagittal planes. Together, our protocols will help scientists in deciphering congenital neurodevelopmental anomalies and anatomical changes between groups of mouse embryos in health and genetic diseases. © 2022 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Fixation and preparation of embryonic mouse brain samples Basic Protocol 2: Sectioning, staining, and scanning of embryonic mouse brain sections Basic Protocol 3: Coronal neuroanatomical measurements of embryonic mouse brain structures Basic Protocol 4: Sagittal neuroanatomical measurements of embryonic mouse brain structures.