Distribution of doublecortin in the developing retina of birds: A comparative analysis.

The avian retina presents an elegant and highly accessible model for investigating the spatial and temporal dynamics of neurogenesis within the central nervous system. In recent years, the microtubule cytoskeleton has emerged not merely as a structural scaffold, but as a dynamic regulator of the transition of a morphologically homogeneous pool of multipotent progenitor cells to postmitotic neurons. Doublecortin (DCX) is a microtubule-associated protein broadly recognized for its fundamental roles in neuronal migration, differentiation, and structural plasticity within the developing nervous system. While its roles in the brain are well-documented, the precise spatiotemporal distribution of DCX in the developing retina of birds remains poorly understood. In this study we investigated the expression pattern of DCX during embryonic development of the retina of one altricial (zebra finch, Taeniopygia guttata) and two precocial (chicken, Gallus gallus; Japanese quail, Coturnix coturnix) bird species using immunohistochemical techniques. Our results demonstrated that the onset of DCX expression coincided chronotopographically with the onset of neurogenesis in the developing retina. In these early stages, DCX expression is tightly colocalized with the neuronal marker class III β-tubulin. As retinal histogenesis progressed to more advanced stages, DCX expression persisted and segregated into specific subsets of ganglion, amacrine, and horizontal cells. Furthermore, prominent immunoreactivity was maintained within the ciliary marginal zone (CMZ), highlighting its association with late-stage retinal progenitors and ongoing neurogenesis. These findings reveal a conserved spatiotemporal expression pattern of DCX across diverse avian species. Furthermore, it suggests that some elements of the cytoskeleton and its associated regulatory proteins form a functional continuous biological continuum: first acting as drivers of neurogenesis and migration and, subsequently, transitioning into structural stabilizers that lock in and maintain the complex morphology of fully differentiated, mature retinal neurons.