One subtype of interneurons, classified by their neurochemical properties, are somatostatin-positive (SST+) interneurons, which express somatostatin along with GABA and form synapses with both pyramidal neurons and other interneurons. SST+ interneurons originate in the medial ganglionic eminence and migrate tangentially to the cortex, making them potentially vulnerable to gene mutations linked to neuronal migration disorders. The Lis1 gene (Pafah1b1) regulates dynein-mediated motility, mitosis, and microtubule organization. Mutations in Lis1 are associated with lissencephaly and cortical disorganization. To investigate its role, we developed a mouse model with Lis1 deletion specifically in SST+ interneurons. We studied the anatomical and developmental effects of this deletion, focusing on tangential migration during embryonic and early postnatal stages. We analyzed SST+ interneuron numbers in the cingulate cortex (anterior and retrosplenial regions) of young mutant mice (P30). Our findings show a reduction in SST+ interneurons in mutants compared to controls, indicating impaired migration and/or maturation. Further research is needed to uncover the mechanisms behind this reduction and to determine its functional implications.

LIS1-lissencephaly is a neurodevelopmental disorder marked by reduced cortical folding and severe neurological impairment. Although all cases result from heterozygous mutations in the LIS1 gene, patients present a broad spectrum of severity. Here, we use patient-derived forebrain organoids representing mild, moderate, and severe LIS1-lissencephaly to uncover mechanisms underlying this variability. We show that LIS1 protein levels vary across patient lines and partly correlate with clinical severity, indicating mutation-specific effects on protein function. Integrated morphological, transcriptomic, and proteomic analyses reveal progressive changes in neural progenitor homeostasis and neurogenesis that scale with severity. Mechanistically, microtubule destabilization disrupts cell-cell junctions and impairs WNT signaling, and defects in protein homeostasis, causing stress from misfolded proteins, emerge as key severity-linked pathways. Pharmacological inhibition of mTORC1 partially rescues these defects. Our findings demonstrate that patient-derived organoids can model disease severity, enabling mechanistic dissection and guiding targeted strategies in neurodevelopmental disorders.

Cytoplasmic dynein-1 (dynein) is an essential molecular motor controlled in part by autoinhibition. Lis1, a key dynein regulator mutated in the neurodevelopmental disease lissencephaly, plays a role in dynein activation. We recently identified a structure of partially autoinhibited dynein bound to Lis1, which suggests an intermediate state in dynein's activation pathway. However, other structural information is needed to fully understand how Lis1 activates dynein. Here, we used cryo-EM and yeast dynein and Lis1 incubated with ATP at different time points to reveal conformations that we propose represent additional intermediate states in dynein's activation pathway. We solved 16 high-resolution structures, including 7 distinct dynein and dynein-Lis1 structures from the same sample. Our data support a model in which Lis1 relieves dynein autoinhibition by increasing its basal ATP hydrolysis rate and promoting conformations compatible with complex assembly and motility. Together, this analysis advances our understanding of dynein activation and the contribution of Lis1 to this process.

The viscoelastic properties of tissues influence their morphology and cellular behavior, yet little is known about changes in these properties during brain malformations. Lissencephaly, a severe cortical malformation caused by LIS1 mutations, results in a smooth cortex. Here, we show that human-derived brain organoids with LIS1 mutation exhibit increased stiffness compared to controls at multiple developmental stages. This stiffening correlates with abnormal extracellular matrix (ECM) expression and organization, as well as elevated water content, measured by diffusion-weighted MRI. Short-term MMP9 treatment reduces both stiffness and water diffusion levels to control values. Additionally, a computational microstructure mechanical model predicts mechanical changes based on ECM organization. These findings suggest that LIS1 plays a critical role in ECM regulation during brain development and that its mutation leads to significant viscoelastic alterations.

Lissencephaly (LIS) is a subtype of malformations of cortical development (MCD), characterized by smooth brain surfaces and underdeveloped gyri and sulci. This study investigates the genetic cause of pachygyria in a Chinese male infant diagnosed with the condition, who previously showed no causative variant through trio whole exome sequencing (Trio-WES) and copy number variation sequencing (CNVseq). Whole-genome sequencing (WGS) was conducted, revealing a novel heterozygous inversion spanning 1.02M bps on chromosome 17 [seq[GRCh37]inv(17)(p13.3p13.2)|NC_000017.10:g.2562761_3581978inv] involving the PAFAH1B1 gene. This de novo variant, confirmed by PCR and Sanger sequencing, was present in the proband but absent in the parents. The inversion disrupts PAFAH1B1, classified as haploinsufficient in the ClinGen database, and is associated with lissencephaly-1 (LIS1) and subcortical band heterotopia (SBH) (OMIM #607432). The findings align with the known characteristics of this disorder, extending the understanding of the molecular mechanisms underlying pachygyria. This identification offers new insights for individuals with developmental delays and brain malformations to uncover the genetic cause of their conditions.