Human doublecortin (DCX) mutations are associated with severe brain malformations leading to aberrant neuron positioning (heterotopia), intellectual disability and epilepsy. The Dcx protein plays a key role in neuronal migration, and hippocampal pyramidal neurons in Dcx knockout (KO) mice are disorganized. The single CA3 pyramidal cell layer observed in wild type (WT) is present as two abnormal layers in the KO, and CA3 KO pyramidal neurons are more excitable than WT. Dcx KO mice also exhibit spontaneous epileptic activity originating in the hippocampus. It is unknown, however, how hyperexcitability arises and why two CA3 layers are observed.Transcriptome analyses were performed to search for perturbed postnatal gene expression, comparing Dcx KO CA3 pyramidal cell layers with WT. Gene expression changes common to both KO layers indicated mitochondria and Golgi apparatus anomalies, as well as increased cell stress. Intriguingly, gene expression analyses also suggested that the KO layers differ significantly from each other, particularly in terms of maturity. Layer-specific molecular markers and BrdU birthdating to mark the final positions of neurons born at distinct timepoints revealed inverted layering of the CA3 region in Dcx KO animals. Notably, many early-born 'outer boundary' neurons are located in an inner position in the Dcx KO CA3, superficial to other pyramidal neurons. This abnormal positioning likely affects cell morphology and connectivity, influencing network function. Dissecting this Dcx KO phenotype sheds light on coordinated developmental mechanisms of neuronal subpopulations, as well as gene expression patterns contributing to a bi-layered malformation associated with epilepsy.
Abstract Motile cells such as immune and cancer cells experience large deformation events that result from the physical constraints they encounter while migrating within tissues or circulating between organs. It has become increasingly clear that these cells can survive and adapt to these changes in cell shape using dedicated shape sensing pathways. However, how shape sensing impacts their function and fate remains largely unknown. Here we identify a shape sensing mechanism that couples cell motility to expression of CCR7, the chemokine receptor that guides immune cells to lymph nodes. We found that this mechanism is controlled by the lipid metabolism enzyme cPLA 2 , requires an intact nuclear envelop and exhibits an exquisitely sensitive activation threshold tuned by ARP2/3 and its inhibitor Arpin. We further show that shape sensing through the ARP2/3-cPLA 2 axis controls Ikkβ-NFκB-dependent transcriptional reprogramming of dendritic cells, which instructs them to migrate to lymph nodes in an immunoregulatory state compatible with their homeostatic tolerogenic function. These results highlight that the cell shape changes experienced by motile cells evolving within the complex environment of tissues can dictate their behavior and fate.
