Cdk5 and its substrates, Dcx and p27kip1, regulate cytoplasmic dilation formation and nuclear elongation in migrating neurons

Abstract

Neuronal migration is crucial for development of the mammalian-specific six-layered cerebral cortex. Migrating neurons are known to exhibit distinct features; they form a cytoplasmic dilation, a structure specific to migrating neurons, at the proximal region of the leading process, followed by nuclear elongation and forward movement. However, the molecular mechanisms of dilation formation and nuclear elongation remain unclear. Using ex vivo chemical inhibitor experiments, we show here that rottlerin, which is widely used as a specific inhibitor for PKCδ, suppresses the formation of a cytoplasmic dilation and nuclear elongation in cortical migrating neurons. Although our previous study showed that cortical neuronal migration depends on Jnk, another downstream target of rottlerin, Jnk inhibition disturbs only the nuclear elongation and forward movement, but not the dilation formation. We found that an unconventional cyclin-dependent kinase, Cdk5, is a novel downstream target of rottlerin, and that pharmacological or knockdown-mediated inhibition of Cdk5 suppresses both the dilation formation and nuclear elongation. We also show that Cdk5 inhibition perturbs endocytic trafficking as well as microtubule organization, both of which have been shown to be required for dilation formation. Furthermore, knockdown of Dcx, a Cdk5 substrate involved in microtubule organization and membrane trafficking, or p27 kip1 , another Cdk5 substrate involved in actin and microtubule organization, disturbs the dilation formation and nuclear elongation. These data suggest that Cdk5 and its substrates, Dcx and p27 kip1 , characterize migrating neuronspecific features, cytoplasmic dilation formation and nuclear elongation in the mouse cerebral cortex, possibly through the regulation of microtubule organization and an endocytic pathway.

p27kip1: An all-round tumor suppressor

“…7 Recent studies in neurons demonstrated that p27 controls the trafficking of Rab5-containing vesicles via regulation of MT organization. 8 In line with these observations, our work provides evidence that cytoplasmic p27, through its interaction with Stathmin, affects Ras activity, favoring its accumulation in Rab-5-positive vesicles and its mono-/bi-ubiquitination. 7 Using different approaches, we demonstrated that the increase in MAPK pathway activity observed in p27 null cells is, at least in part, dependent on MTdependent transport.…”

The Role of Cdk5 in Alzheimer’s Disease

“…Cdk5 is considered as an important regulator of mitochondrial morphology via inhibitory phosphorylation of Drp1S616 in post-mitotic neurons [30]. Furthermore, Cdk5 and its substrates, Dcx and p27 (kip1), characterize modulating cytoplasmic dilation formation and nuclear elongation in migrating neurons, possibly via regulating microtubule organization and an endocytic pathway [31]. The Cdk5/p35 complex may make a significant contribution to regulation of Hif-1α stabilization and influence neuronal survival during Cdk5 is a multi-function kinase that is implicated in neuron survival and death.…”

Morphological and Molecular Basis of Cytoplasmic Dilation and Swelling in Cortical Migrating Neurons

“…Locomoting neurons show neuron-specific unique migration features [ 12 , 13 , 17 ]. (1) Locomoting neurons extend a leading process and form a cytoplasmic “dilation” (also known as a “swelling”) at the proximal region of their leading process; (2) The nuclei in the locomoting neurons elongate to enter the cytoplasmic dilation.…”

“…Recently, several in vitro and ex vivo techniques, allowing direct analysis of molecules involved in the locomotion mode, have been established. These include explant culture [ 12 ], slice culture-based ex vivo chemical inhibitor technique [ 11 , 13 ], lattice culture [ 14 , 15 ], co-culture of primary cortical excitatory neurons and nestin-positive cells [ 16 ], co-culture of MGE explants on dissociated cortical neurons with elongated axons [ 17 ] and cortical imprint assay [ 18 ].…”