Oregon Health & Science UniversityNervous
The STe20-Related ADapter (STRAD) pseudokinases are highly evolutionarily conserved regulators of the protein kinase LKB1, but the roles of the vertebrate paralogs STRADα and STRADβ in the developing nervous system are not fully defined, nor is it known whether they serve distinct functions given their high degree of homology. Our phylogenetic analysis indicates that STRADα is the primal STRAD gene with STRADβ appearing following a gene duplication event solely in vertebrate species. The discovery and description of a hereditary developmental epilepsy syndrome known as Polyhydramnios, Megalencephaly, and Symptomatic Epilepsy (PMSE) Syndrome caused by homozygous deletion of part of the STRADα gene (Puffenberger et al., 2007) indicates that this family of proteins plays a key role in development. I conducted biochemical and genetic analyses to better understand the contribution of the STRAD pseudokinases to vertebrate brain patterning. Here I report a novel STRADα splice variant, STRADα-7, as well as assigning tissue specificity to a previously reported splice variant, STRADα-1. Each splice form of STRADα and STRADβ was sufficient to potentiate axogenesis, and both STRADs promoted cell survival in the developing cortex. We also found a reciprocal proteinstabilizing relationship in vivo between LKB1 and STRADα, whereby STRADα specifically maintains LKB1 protein levels via cytoplasmic compartmentalization and control of nuclear export. We demonstrate for the first time, that STRADβ is sufficient for axogenesis, and that STRADα, but not STRADβ, is responsible for LKB1 protein stability in vivo. We also examined the regulation of the STRAD proteins by another protein, Cerebral Cavernous Malformations 3/ProgrammeD Cell Death 10 (CCM3/PDCD10). CCM3 had differential effects on STRADa and STRADβ, suggesting that it acts to fine-tune LKB1 activity. There are myriad causes of developmental epilepsy, both environmental and genetic. Hereditary epilepsies can be studied to better understand the genetic mechanisms underlying these diseases, and to perhaps generate effective interventions. We generated knockout mice of STRADα and its family member, STRADβ, as mouse models for this human disease, and to begin to outline the epileptic mechanism. We also examined the timing of STRADα and STRADβ deletion and their effects on gross corticogenesis and show that timing and mode of deletion of STRADα determined its effects on cortical development, indicating tight developmental control of STRAD expression. A partial redundancy between STRADα and STRADβ was observed in the context of cortical lamination. Furthermore, loss of both STRADα and STRADβ did not phenocopy LKB1. Taken together, our data provide a richer understanding of the expression and function of the STRAD pseudokinases in the developing brain.
Neuroscience Graduate Program
School of Medicine
Veleva-Rotse, Biliana O., "Strad pseudokinases are critical in embroyonic brain development and in regulating LKB1 stability" (2015). Scholar Archive. 3604.
Available for download on Tuesday, January 16, 2018