The neuroanatomy of Eml1 knockout mice, a model of subcortical heterotopia

Abstract

The cerebral cortex is a highly organized structure responsible for advanced cognitive functions. Its development relies on a series of steps including neural progenitor cell proliferation, neuronal migration, axonal outgrowth and brain wiring. Disruption of these steps leads to cortical malformations, often associated with intellectual disability and epilepsy. We have generated a new resource to shed further light on subcortical heterotopia, a malformation characterized by abnormal neuronal position. We describe here the generation and characterization of a knockout (KO) mouse model for Eml1, a microtubule-associated protein showing mutations in human ribbon-like subcortical heterotopia. As previously reported for a spontaneous mouse mutant showing a mutation in Eml1, we observe severe cortical heterotopia in the KO. We also observe abnormal progenitor cells in early corticogenesis, likely to be the origin of the defects. EML1 KO mice on the C57BL/6N genetic background also appear to present a wider phenotype than the original mouse mutant, showing additional brain anomalies, such as corpus callosum abnormalities. We compare the anatomy of male and female mice and also study heterozygote animals. This new resource will help unravel roles for Eml1 in brain development and tissue architecture, as well as the mechanisms leading to severe subcortical heterotopia.The following primers were used for genotyping ( Fig. S1):

Echinoderm Microtubule Associated Protein Like 1 Is Indispensable for Oocyte Spindle Assembly and Meiotic Progression in Mice

“…In a spontaneous mouse mutant model where the expression of Eml1 was disrupted by a transposon insertion, the localization of γ-tubulin and the length of metaphase spindles were also found to be altered in the apical progenitors of the developing cerebral cortex (Kielar et al, 2014;Collins et al, 2019). But the spindles in this mutant brain cells were abnormally long, which was opposite to what we observed here in the oocytes with EML1 knocked down.…”

“…Until recently, the physiological role of this family protein was starting to be appreciated, as the disease-and developmental disorder causingmutations and deletions of the EML encoding genes were gradually discovered (De Keersmaecker et al, 2005;Lin et al, 2009;Sun et al, 2015). Of particularly, for instance, deletions or losses of function of EML1 in mouse, rat, and human cause subcortical heterotopia in the brain or disorganization of retina architecture in the eye, which is probably brought by defects in primary cilia formation, mitotic spindle length/positioning and proliferation of neuronal progenitors, and lamination of the inner retina (Eudy et al, 1997;Kielar et al, 2014;Bizzotto et al, 2017;Collins et al, 2019;Oegema et al, 2019;Uzquiano et al, 2019;Collin et al, 2020;Grosenbaugh et al, 2020). Unfortunately, these interesting new findings were all on somatic cells, the function of EMLs in oocytes remained virtually unknown.…”

Roots of the Malformations of Cortical Development in the Cell Biology of Neural Progenitor Cells

“…EML1 (echinoderm microtubule associated protein-like 1) is a microtubule-associated protein whose mutation leads to complex cortical malformations characterized by megalencephaly with a ribbon-like heterotopia and callosal agenesis ( Kielar et al, 2014 ; Oegema et al, 2019 ). The spontaneously arisen mutant mice (HeCo mice) and KO mouse models recapitulate the heterotopia phenotype ( Kielar et al, 2014 ; Collins et al, 2019 ). HeCo mice are characterized by a perturbation of microtubule dynamics and an increase in oblique cleavage orientations of aRG, that lead to ectopic proliferation of progenitor cells in IZ and CP ( Kielar et al, 2014 ; Bizzotto et al, 2017 ).…”

Quantitative Neuroanatomical Phenotyping of the Embryonic Mouse Brain

“…Using these protocols, we have processed 288 embryonic mouse brain samples to date, representing 144 mutant and 144 wild‐type samples, all on C57BL/6N backgrounds for 12 unique gene mutations. Here, we illustrate three examples of genes ( Eml1 , Wdr91 , and Wdr47 ) belonging to the WD40‐repeat gene family, which is characterized by seven repetitive blades of 40 amino acids that end with a tryptophan‐aspartic acid dipeptide at the C terminus, which is enriched in neurodevelopmental anomalies (Collins, Uzquiano, et al., 2019; Kannan et al., 2017). Key results are summarized, which were obtained for Eml1 , Wdr91 , and Wdr47 full knockout embryos, ordered here from extremely severe ( Eml1 ) to very severe ( Wdr91 ) to severe ( Wdr47 ) brain anatomical perturbations.…”