Optic tectum morphogenesis: a step-by-step model based on the temporal-spatial organization of the cell proliferation. Significance of deterministic and stochastic components subsumed in the spatial organization.

BACKGROUND: Cell proliferation plays an important morphogenetic role. This work analyzes the temporal-spatial organization of cell proliferation as an attempt to understand its contribution to the chick optic tectum (OT) morphogenesis. RESULTS: A morphogenetic model based on space-dependent differences in cell proliferation is presented. Step1: a medial zone of high mitotic density (mZHMD) appears at the caudal zone. Step2: the mZHMD expands cephalically forming the dorsal curvature and then duplicates into two bilateral ZHMDs (bZHMD). Step3: the bZHMDs move toward the central region of each hemitectum. Step4: the planar expansion of both bZHMD and a relative decrement in the dorsal midline growth produces a dorsal medial groove separating the tectal hemispheres. Step5: a relative caudal displacement of the bZHMDs produces the OT caudal curvature. Numerical sequences derived from records of mitotic cells spatial coordinates, analyzed as stochastic point processes, show that they correspond to 1/f((ß)) processes. The spatial organization subsumes deterministic and stochastic components. CONCLUSIONS: The deterministic component describes the presence of a long-range influence that installs an asymmetric distribution of cell proliferation, i.e., an asymmetrically located ZHMD that print space-dependent differences onto the tectal corticogenesis. The stochastic component reveals short-range anti-correlations reflecting spatial clusterization and synchronization between neighboring cells.

Spatiotemporal analysis of the protein expression of angiogenic factors and their related receptors during folliculogenesis in rats with and without hormonal treatment.

This study investigated the protein expression and cellular localization of ANGPT1, ANGPT2, and their receptor TEK, as well as vascular endothelial growth factor A (VEGFA) and its receptor KDR (VEGFR2) during folliculogenesis. To obtain follicles at different stages for immunochemistry and western analyses, we used prepubertal untreated, diethylstilbestrol- and equine chorionic gonadotropin-treated rats. To confirm that these hormonal treatments reflect physiological change, we used non-treated adult rats. No expression of ANGPT1 was observed in granulosa cells (Gc) from immature hormone-treated and non-treated rats at any follicular stage. By contrast, ANGPT1 expression in theca cells (Tc) increased with follicular maturation. ANGPT2 protein was either absent or weakly expressed in Gc at all follicular stages. In Tc, minimal expression of ANGPT2 protein was detected in the preantral follicle (PF), whereas it was stronger in the early antral follicle (EAF) and preovulatory follicle (POF). TEK staining was absent in Gc but was intense in Tc at every follicular stage. Staining for VEGFA was either absent or weakly present in Gc and Tc in PF and EAF, although in POF it was stronger in Gc and Tc. Staining for KDR was absent in Gc and very low in Tc from PF. Gc and Tc of EAF showed positive staining for KDR and in POF the staining was stronger. These results were confirmed by western immunoblot. A similar pattern of expression of these proteins was observed in cycling rats. In conclusion, we observed that the protein expression of ANGPT1, ANGPT2, VEGFA and their receptors increased during follicular development in rats.

Regulation of ovarian angiogenesis and apoptosis by GnRH-I analogs.

An adequate vascular supply is important to provide endocrine and paracrine signals during follicular development. We evaluated the direct in vivo effects of both the GnRH-agonist Leuprolide acetate (LA) and the GnRH-antagonist Antide (Ant) on the expression of VEGF-A and ANPT-1 and their receptors in ovarian follicles from prepubertal eCG-treated rats. We also examined whether the changes observed in apoptosis by GnRH-I analogs have an effect on the caspase cascade. LA significantly decreased the levels of VEGF-A, its receptor Flk-1, and ANPT-1 when compared to controls, while the co-injection of Ant interfered with this effect. No changes were observed in the levels of Tie-2 after treatment with these analogs. When we measured the follicular content of caspase-3 protein, we observed that LA significantly increased the level of the active form. The co-injection of Ant interfered with this effect and Ant alone significantly decreased caspase-3 cleavage. IHC analyses corroborated these data. Notably, while LA increased caspase-3 activity levels, Ant decreased them when compared to controls. In follicles obtained from LA-treated rats, cleavage of PARP (a substrate of caspase-3) from the intact 113-kDa protein showed a significant enhancement in an 85-kDa fragment. The co-injection of Ant interfered with this effect. Ant alone significantly decreased PARP cleavage as compared to controls. We conclude that the decrease in VEGF-A, its receptor Flk-1/KDR, and ANPT-1 produced by the administration of GnRH-I agonist is one of the mechanisms involved in ovarian cell apoptosis. This suggests an intraovarian role of an endogenous GnRH-like peptide in gonadotropin-induced follicular development.

Temporal-spatial correlation between angiogenesis and corticogenesis in the developing chick optic tectum.

The developing chick optic tectum is a widely used model of corticogenesis and angiogenesis. Cell behaviors involved in corticogenesis and angiogenesis share several regulatory mechanisms. In this way the 3D organizations of both systems adapt to each other. The consensus about the temporally and spatially organized progression of the optic tectum corticogenesis contrasts with the discrepancies about the spatial organization of its vascular bed as a function of the time. In order to find out spatial and temporal correlations between corticogenesis and angiogenesis, several methodological approaches were applied to analyze the dynamic of angiogenesis in the developing chick optic tectum. The present paper shows that a typical sequence of developmental events characterizes the optic tectum angiogenesis. The first phase, formation of the primitive vascular bed, takes place during the early stages of the tectal corticogenesis along which the large efferent neurons appear and begin their early differentiation. The second phase, remodeling and elaboration of the definitive vascular bed, occurs during the increase in complexity associated to the elaboration of the local circuit networks. The present results show that, apart from the well-known influence of the dorsal-ventral and radial axes as reference systems for the spatial organization of optic tectum angiogenesis, the cephalic-caudal axis also exerts a significant asymmetric influence. The term cortico-angiogenesis to describe the entire process is justified by the fact that tight correlations are found between specific corticogenic and angiogenic events and they take place simultaneously at the same position along the cephalic-caudal and radial axes.

The chick optic tectum developmental stages. A dynamic table based on temporal- and spatial-dependent histogenetic changes: A structural, morphometric and immunocytochemical analysis.

Development is often described as temporal sequences of developmental stages (DSs). When tables of DS are defined exclusively in the time domain they cannot discriminate histogenetic differences between different positions along a spatial reference axis. We introduce a table of DSs for the developing chick optic tectum (OT) based on time- and space-dependent changes in quantitative morphometric parameters, qualitative histogenetic features and immunocytochemical pattern of several developmentally active molecules (Notch1, Hes5, NeuroD1, ß-III-Tubulin, synaptotagmin-I and neurofilament-M). Seven DSs and four transitional stages were defined from ED2 to ED12, when the basic OT cortical organization is established, along a spatial developmental gradient axis extending between a zone of maximal and a zone of minimal development. The table of DSs reveals that DSs do not only progress as a function of time but also display a spatially organized propagation along the developmental gradient axis. The complex and dynamic character of the OT development is documented by the fact that several DSs are simultaneously present at any ED or any embryonic stage. The table of DSs allows interpreting how developmental cell behaviors are temporally and spatially organized and explains how different DSs appear as a function of both time and space. The table of DSs provides a reference system to characterize the OT corticogenesis and to reliably compare observations made in different specimens.