OVEREXPRESSION OF ANOSMIN-1 ALTERS THE MYELINATION PATTERN AND THE MORPHOLOGY OF AXONAL COMPONENTS IN CEREBELLAR PURKINJE CELLS

Anosmin-1 (A1) is an extracellular matrix glycoprotein that regulates FGF, Wnt, BMP, and VEGF signaling pathways during nervous system development, and is widely expressed throughout the central nervous system, including the cerebellum. Mutations in the ANOS1 gene (formerly KAL1), which encodes A1, cause Kallmann syndrome (KS), a rare congenital disorder characterized by hypogonadotropic hypogonadism and anosmia. Given that the A1-overexpressing mouse model exhibits ataxia-like motor deficits, we hypothesized that these abnormalities might result from cerebellar dysfunction. Alterations in myelin formation and in the structural components of axons are major contributors to both the generation and conduction velocity of action potentials and may represent a key mechanism underlying the motor impairments observed in A1-overexpressing mice. To investigate this possibility, we examined the maturation dynamics of the axon initial segment (AIS) and the overall myelination pattern. Immunostaining of Ankyrin-g, a reliable marker of the AIS, revealed distinct morphological modifications in Purkinje cell axons of A1-overexpressing mice. Specifically, AISs in mutant mice are significantly longer and located further away from the soma compared to wild-type (WT) controls at adult stages. To assess potential structural modifications in the nodal and paranodal regions, we measured the length of nodes of Ranvier and found that, at postnatal day 60, mutant mice displayed longer nodes compared to WT. Moreover, during development, A1-overexpressing mice exhibited an altered timeline of myelination with evidence that the deposition occurs earlier compared to WT. Yet, in the mutants myelination reaches normal levels at adult stages. These data indicate that A1 regulates both the timing of myelin deposition and the structural organization of axonal domains, thereby participating in the neuromorphological shaping of Purkinje cell axons essential for efficient signal transmission.