Here we will discuss the aspects of patterning the morphogenic cell behaviours that close the blastopore during gastrulation of amphibians. Spemann (1938) distinguished between patterning of morphogenesis, which he referred to as ‘dynamic determination’ of regionally autonomous ‘formative tendencies’, and patterning of tissue types, which he referred to as ‘material determination’, and he discussed at length how the two might be related. Patterning is often thought of as the process of specifying a region of the embryo to differentiate into a particular cell or tissue type, but in the context of morphogenesis, patterning is the specification of a dynamic, spatio-temporal pattern of cell behaviours and tissue properties that generate and transmit the forces driving morphogenic (shape generating) processes. Understanding the patterning of these dynamic features of cell behaviour is important and will require analysis of signalling at much greater spatial and temporal resolution than that has been typical in the analysis of patterning tissue differentiation. It is not the nature of the cell behaviour alone, but the context, the biomechanical connectivity and spatial and temporal pattern of its expression that determine specificity of morphogenic output during gastrulation and blastopore closure. They are expressed progressively along presumptive lateral–medial and anterior–posterior axes of the body plan in highly ordered geometries of functional significance in the context of the biomechanics of blastopore closure, thereby accounting for the production of similar patterns of circumblastoporal forces. Although these cell behaviours are quite different and involve different germ layers and tissue organization, they are expressed in similar patterns. Mediolateral cell intercalation behaviour and epithelial–mesenchymal transition are used in different combinations in several species of amphibian to generate a conserved pattern of circumblastoporal hoop stresses. The present study suggested that (i) the dorsal determinants consist of blastopore-forming and dorsal mesoderm-inducing factors, which are not always mutually dependent (ii) both factors are activated during the late blastula stage (iii) the dorsal marginal zone cannot specify to an organized notochord and muscle without the involution that blastopore formation leads to and (iv) the localization of both factors in the same place is prerequisite for dorsal axis formation.We review the dynamic patterns of cell behaviours in the marginal zone of amphibians with a focus on how the progressive nature and the geometry of these behaviours drive blastopore closure. bra expression was activated in the nocodazole-treated embryos but not in the suramin-injected embryos. In contrast, the LDMZ of the suramin-injected embryos lost its dorsal mesoderm-inducing activity. The dorsal mesoderm-inducing activity of the LDMZ in the nocodazole-treated gastrulae was still active. Suramin-injected and nocodazole-treated blastulae did not have involution of the dorsal marginal zone, although the blastopore was formed. These embryos were rescued by artificially facilitating involution of the dorsal marginal zone. Involution of the dorsal marginal zone was disturbed by the abnormal blastopore. Ultraviolet-irradiated eggs formed an abnormal blastopore and then did not form a dorsal axis, although the lower dorsal marginal zone (LDMZ) still had dorsal mesoderm-inducing activity. It was confirmed that the isolated dorsal C and D blastomeres autonomously formed a blastopore. The blastopore-forming (bottle) cells originated mainly from the progeny of the mid-dorsal C and/or D blastomeres of the 32-cell embryo, but were not defined to a fixed blastomere. The independent roles of blastopore formation and dorsal mesoderm induction in dorsal axis formation of the Cynops pyrrhogaster embryo were attempted to be clarified.
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