The dynamics of the spatial distribution of histogenetic stages during the chick optic tectum corticogenesis. Immunohistochemical characterization

RAPACIOLI, MELINA; RODRIGUEZ CELIN, ALEJANDRA; DUARTE, SANTIAGO; ORTALLI, ANA L; TERUEL, LUISA R; SANCHEZ, VIVIANA; SCICOLONE, GABRIEL; FLORES, VLADIMIR

Buenos Aires, Argentina

Congreso; 4th International Meeting of the Latin American Society of Developmental Biology.; 2008

Latin American Society of Developmental Biology

The dynamics of the spatial distribution of histogenetic stages during the  chick optic tectum corticogenesis. Immunohistochemical characterization. Rapacioli M 1, Rodrgíguez Celín A 1, Duarte S 2, Ortalli A 2, Teruel L 2, Sánchez V 2, Scicolone G 2, Flores V 1,2. Introduction. The avian optic tectum (OT) is a widely used experimental model in developmental neurosciences. It possesses a cortical organization whose development starts as a simple neuroepithelium and progresses through increasingly complex multilaminated patterns. Although it is widely accepted that its development proceeds according to a ventrolateral to dorsomedial developmental gradient, morphological studies on the developing chick OT usually disagree in many respects. Our hyptothesis is that discrepancies frequently arise from the fact that development progression is usually described only as a function of time and that the spatial complexity is usually disregarded. Objectives. (a) Definition of a table of developmental histogenetic stages (DHS) of the OT. This table can be used to avoid inappropriate comparisons, (b) Validation of the hypothesis that the DHS progresses not only as a function of time but also propagates as a function of space. This implies that different DHS coexist at the same time but localized at different positions along the spatial axes. (c) Characterization of the spatial pattern of expression of several developmental informative molecules and their association with particular DHS. Methods. The methodology implies: 1. Analyses of spatially oriented complete histological serial sections of OTs of different developmental ages (Embryonic days 2 through 12). 2. Adjacent sections were processed for H-E staining and by immunohistochemical methods for detection of several molecules involved in neuroepithelial cell proliferation, neuronal migration  and neuron differentiation (Notch, Hes5, BTG2, NeuroD, several integrin subunits, uPA-receptor, MMP2). 3. Definition of DHS on the bases of qualitative histogenetic features and morphometric parameters. 4. Demarcation of each DHS on sections of OT of different ages. 5. Construction of 2D maps of DHS distribution. 6. Assembly of 2D maps of DHS as a function of the Z axis and construction of 3D virtual OT replicas. Results. Analyses of 3D virtual OT replicas demonstrate that: 1. Several DHS coexists at any developmental age analyzed. 2. These different DHS show a characteristic spatial organization along the cephalic-caudal and the dorso-ventral axes. 3. Each DHS first appears at a site of maximal development, close to the zone of the optic nerve entry, and from this site propagates, as a wave, through the OT lateral and medial surfaces, towards the caudal zone of the dorsal midline. 4. Immunohistochemical methods help to characterize patterns of cell behaviors operating at different DHS. Conclusions. Given that the OT corticogenesis progresses and propagates as a function of both, time and space, both parameters must be taken into account in order to make appropriate comparisons between different observations. As a whole our results indicate that it is advisable to always specify several parameters as references to guarantee appropriate comparisons: a) embryonic age, b) embryonic developmental stage, c) OT DHS and d) specific position of the region under analysis along each spatial reference axis. Without these specifications any comparison could be considered as potentially inappropriate. Supported by grants from CONICET and UBACYT (Argentina)