Date of Award

2025

Document Type

Open Access Thesis

Department

Biological Sciences

First Advisor

Deanna Smith

Abstract

Proper LIS1 function is crucial for human brain development, as mutations in LIS1 lead to lissencephaly, a severe neurodevelopmental disorder caused by defective proliferation, differentiation and migration of neural precursors. Our understanding of LIS1's functions after brain development is limited. LIS1 regulates cytoplasmic dynein 1 (dynein), an essential microtubule motor protein in cell division and migration, but also a cellular transport motor. We previously showed that tamoxifen (TX)-induced global knockout of LIS1 using a Cre/Lox system (Act-Lis1iKO) in young adult mice results in severe neurological defects and rapid lethality. This strongly supports LIS1's critical post- developmental role, but the underlying cellular defects causing the severe phenotypes remain unknown. For my thesis project I worked on a study in which LIS1 was depleted specifically in mature projection neurons using a thy1 promoter to drive TX-inducible Cre recombinase (Thy1-Lis1iKO). This study demonstrates the LIS1 loss in these cells was the primary underlying cause of the observed Act-Lis1iKO phenotypes. Homozygous iKO mice exhibited clear neurological phenotypes, including severe shivering and leg clasping behaviors, followed by seizures and ultimately death within 10 days after the initial injection. Control littermates or mice with LIS1 depleted from astrocytes instead of neurons did not have severe neurological phenotypes and did not die, reaffirming that LIS1 depletion in projection neurons was the primary cause of the observed Act-Lis1iKO phenotypes. Most studies with the Thy1-Lis1iKO mice involved 5 consecutive daily injections of TX. Reducing this to 3 consecutive TX injections produced a less severe phenotype and longer survival. . Crossing mice with a fluorescent Cre activity reporter indicates this TX dose activates Cre in fewer neurons. At the time severe neurological symptoms were displayed in mice receiving 5 TX injections, axons throughout the PNS and CNS had a beaded appearance and appeared fragmented. Axons were also immunoreactive for an antibody that recognizes a neurofilament epitope normally only seen in degenerating axons (Degenotag). Cultured DRGs from Thy1-Lis1iKO mice receiving 4 injections also displayed a beaded appearance and were immunoreactive for Degenotag. Application of SARM1 inhibitor drug to these cultures reduced axonal swellings observed. Together this work demonstrates that LIS1 is a critically important protein in young adult mouse projection neurons and is required for axonal maintenance.

Rights

© 2025, Anne Ventrone

Download

Included in

Neurosciences Commons

Share

COinS