Regional Specification of the Head and Trunk–Tail Organizers of a Urodele (Cynops pyrrhogaster) Embryo Is Patterned during Gastrulation

Abstract

The dorsal marginal zone (DMZ) of an amphibian early gastrula is thought to consist of at least two distinct domains: the future head and trunk-tail organizers. We studied the mechanism by which the organizing activities of the lower half of the DMZ (LDMZ) of the urodelean (Cynops pyrrhogaster) embryo are changed. The uninvoluted LDMZ induces the notochord and then organizes the trunk-tail structures, whereas after cultivation in vitro or suramin treatment, the same LDMZ loses the notochord-inducing ability and organizes the head structures. A cell-lineage experiment indicated that the change in the organizing activity of the LDMZ was reflected in the transformation of the inductive ability: from notochord-inducing to neural-inducing activity. Using RT-PCR, we showed that the LDMZ expressed gsc, lim-1, chordin, and noggin, but not the mesoderm marker bra. In the sandwich assay, the LDMZ induced bra expression in the animal cap ectoderm, but the inductive activity was inhibited by cultivation or suramin treatment. The present study indicates that the change in the organizing activity of the LDMZ from trunk-tail to head is coupled with the loss of notochord-inducing activity. Based on these results, we suggest that this change is essential for the specification of the head and trunk-tail organizers during gastrulation.

Gastrulation and pre-gastrulation morphogenesis, inductions, and gene expression: Similarities and dissimilarities between urodelean and anuran embryos

“…Much later, dividing the Cynops early gastrula DMZ into the UDMZ and LDMZ further confirmed that the LDMZ selfdifferentiates into an endodermal cell mass, but has potent notochord-inducing activity (Fig. 8), and that the UDMZ has epidermal self-differentiation capacity (Kaneda, 1981;Kaneda and Suzuki, 1983;Suzuki et al, 1984;Kaneda et al, 2002Kaneda et al, , 2009Sakaguchi et al, 2002).…”

“…Suzuki et al, 2002), while the notochord-inducing activity of the LDMZ remains active . Suzuki et al (2002) treated Cynops embryos with anti-morphogenesis reagents such as suramin (aspecific FGF-inhibitor, Gerhart et al, 1991;Grunz, 1992;Oschwald et al, 1993;Cardellini et al, 1994;Wallingford et al, 1997;Kaneda et al, 2002;Sakaguchi et al, 2002) or nocodazole (inhibitor for microtubule polymerization, Lane and Keller, 1997). Suramin injection and nocodazole treatment inhibited involution of the DMZ, but the blastopore formed normally.…”

“…Although the embryonic stage, isolation size, spatial localization and methods of identifying the self-differentiation and organizing capacities vary among studies according to the defining criteria used, the self-differentiation and organizing activities of the early gastrula DMZ have been extensively analyzed in many urodeles (e.g., Spemann and Mangold, 1924;Holtfreter, 1938a;Holtfreter-Ban, 1965;Kaneda and Hama, 1979;Kaneda, 1980Kaneda, , 1981Slack, 1984;Cleine and Slack, 1985;Hama et al, 1985;Delarue et al, 1992;Yamamoto and Suzuki, 1994;Imoh et al, 1998;Kaneda et al, 2002Kaneda et al, , 2009 and in anura species (e.g., Holtfreter, 1938b;Smith and Slack, 1983;Gerhart, 1990, 1991;Shih and Keller, 1992;Domingo and Keller, 1995;Lane and Keller, 1997;Manes and Campos Casal, 1997;Fujii et al, 2002). By inserting the DLP into the blastocoel, earlier experiments revealed that the DLP of the early gastrula has secondary axis organizing activity in which the inserted DLP differentiates into notochord, somites and endoderm, while the secondary neural axis originates from the host embryo (e.g., Spemann and Mangold, 1924).…”

Morphogenic machines evolve more rapidly than the signals that pattern them: lessons from amphibians

“…For example, the initial symmetry breaking mechanism giving rise to the embryonic dorsal-ventral axis (Elinson and Rowning, '88;Houliston and Elinson, '91;Iwao et al, '97;Elinson and Ninomiya, 2003;Weaver and Kimelman, 2004;Heasman, 2006), the expression of Brachyury in presumptive mesoderm before involution, and in the extending notochord after involution (Smith et al, '91;del Pino, '96;Tabata et al, 2001;Kaneda et al, 2002;Johnson et al, 2003;Moya et al, 2007) and the expression of Lim1 in the organizer (Taira et al, '92;Tabata et al, 2001;Kaneda et al, 2002;Hukriede et al, 2003;Langeland et al, 2006;del Pino et al, 2007) are all well conserved among the anurans and urodeles. In some cases the conservation of patterning also seems to translate to the conservation of the spatio-temporal pattern of cell behaviors, as noted above for MIB and Subduction.…”

The role of the Spemann organizer in anterior–posterior patterning of the trunk

“…In an early model, it was postulated that different portions of the organizer mediate different positional values along the AP axis (Mangold, 1933;Eyal-Giladi, 1954). Head, trunk, and tail organizing areas have been described in the Xenopus organizer (Zoltewicz and Gerhart, 1997;Lane and Keller, 1997) and other vertebrates (Agathon et al, 2003;Kaneda et al, 2002). Vertical signals from different portions of the internalized organizer mesoderm to the overlying prospective neurectoderm have been suggested for regulation of a few, very anterior patterning genes (Hemmati-Brivanlou et al, 1990;Blitz and Cho, 1995).…”