The Microtubule Minus-End-Binding Protein Patronin/PTRN-1 Is Required for Axon Regeneration in C. elegans

Abstract

Summary Precise regulation of microtubule (MT) dynamics is increasingly recognized as a critical determinant of axon regeneration. In contrast to developing neurons, mature axons exhibit noncentrosomal microtubule nucleation. The factors regulating noncentrosomal MT architecture in axon regeneration remain poorly understood. We report that PTRN-1, the C. elegans member of the Patronin/Nezha/CAMSAP family of microtubule minus end binding proteins, is critical for efficient axon regeneration in vivo. ptrn-1 null mutants display generally normal developmental axon outgrowth but significantly impaired regenerative regrowth after laser axotomy. Unexpectedly, mature axons in ptrn-1 mutants display elevated numbers of dynamic axonal MT before and after injury, suggesting PTRN-1 inhibits MT dynamics. The CKK domain of PTRN-1 is necessary and sufficient for its functions in axon regeneration and MT dynamics, and appears to stabilize MTs independent of minus end localization. Whereas in developing neurons PTRN-1 inhibits activity of the DLK-1 MAPK cascade, we find that in regeneration PTRN-1 and DLK-1 function together to promote axonal regrowth.

The Genetics of Axon Guidance and Axon Regeneration in Caenorhabditis elegans

“…Regrowth initiation is impaired in animals with a gain of function mutation in mec-7/ b-tubulin (Kirszenblat et al 2013). Axon regeneration is also dependent on function of the MT minus end binding protein PTRN-1, a member of the Patronin/CAMSAP family (Chuang et al 2014). ptrn-1 null mutants display minor abnormalities in axon development (Marcette et al 2014;Richardson et al 2014), but are severely impaired in regeneration.…”

Microtubule Minus-End-Targeting Proteins

“…CAMSAP homologues are present in the genomes of all sequenced eumetazoa (animals with tissues) [33]; furthermore, the CKK domain can be found in the sequenced genomes of diverse unicellular organisms, suggesting an ancient evolutionary origin. In worms, overexpression of the CKK domain is necessary and sufficient to rescue the function of the Patronin homologue during axon regeneration, supporting its important function [42]. (A) Schemes of CAMSAP/Patronin/Nezha proteins from three different organisms are shown.…”

“…The localization and function of CAMSAPs/Patronin was analyzed in detail in mammalian and in Caenorhabitis elegans neurons [39][40][41][42]. In cultured mammalian hippocampal neurons, CAMSAP2 -the predominant CAMSAP family member in this cell type -is distributed as small puncta and clusters at early developmental stages and as long (>10 mm) stretches in more mature neurons [39].…”

“…In this review, we discuss how the identification and characterization of these factors has advanced our understanding of microtubule minus-end dynamics and has helped to demonstrate the importance of microtubule minus-end regulation in the control of mitotic spindle length [34][35][36], epithelial cell migration and proper organelle distribution [37,38], and neuronal development and regeneration [39][40][41][42].…”

Noncentrosomal microtubules in C. elegans epithelia

“…C. elegans possesses three known -TIPs (Box 1): g-tubulin and its associated proteins GIP-1 and GIP-2 (Hannak et al, 2002), PTRN-1 [belonging to the conserved Patronin/ Nehza/calmodulin and spectrin-associated family (CAMSAP) (Goodwin and Vale, 2010)], and NOCA-1(noncentrosomal array 1) with homology to ninein (Wang et al, 2015). PTRN-1 function has mostly been described in neurons (Marcette et al, 2014;Richardson et al, 2014), and axon regeneration (Chuang et al, 2014). NOCA-1 was initially identified in the same cluster as g-tubulin and dynein after multiparametric profiling of the results of a screen for germline defects (Green et al, 2011).…”