Comparative study of sequential expression of the organizer‐related genes in normal Cynops pyrrhogaster embryos and mesodermalized ectoderm

Abstract

An artificially mesodermalized ectoderm (mE) of early Cynops pyrrhogaster gastrula acquires the organizer property; the mE is able to induce the secondary axis. The expression of organizer-related genes was investigated during the mesodermalizing process of the mE. The expression of C. pyrrhogaster organizer-related genes, such as bra, gsc, lim-1, chd and noggin, were analyzed. Cynops pyrrhogaster shh expression was also investigated. The organizer-related genes were activated by 12 h after the mesoderm-inducing stimulus. It was noted that there was a temporal gap in the expression of each gene. The expression of bra and gsc seemed to be more quickly activated during the mesodermalizing process. While expression of lim-1 and noggin was activated later than that of bra and gsc, lim-1 expression was earlier than chd and noggin expression. Shh expression was activated later than lim-1/noggin. The present study suggests the possibility that the bra/gsc, lim-1, chd, noggin and shh genes are expressed one by one in that order during the mesodermalizing of the presumptive ectoderm. It also indicates that the sequence is not always consistent with that of the whole embryo during normal embryogenesis. The meaning of the discrepancy will be discussed in connection with the cascade of certain genes expressed during the mesodermalizing process.

Blastopore formation and dorsal mesoderm induction are independent events in early Cynops embryogenesis

“…In Cynops embryos, gsc and bra genes are expressed during the mesodermalizing process (Sone et al 1997;Yokota et al 1998;Tabata et al 2001;Kaneda et al 2002). It has been indicated that bra is not expressed at the early gastrula stage, but its expression is detected in the area corresponding to the prospective notochord of the advanced gastrula (Sone et al 1997;Yokota et al 1998;Doi et al 2000;Tabata et al 2001). Neither invagination nor involution movements were observed in the suramin-treated gastrulae.…”

“…To compare the expressions of gsc , bra , α‐actin and N‐CAM , the total RNA extracted from one embryo of each sample was used for reverse transcription (RT)–polymerase chain reaction (PCR). Total RNA isolation and RT–PCR have been previously described (Tabata et al . 2001).…”

“…2001). The primer sequences used for the marker genes were as follows: bra (Tabata et al . 2001), gsc (Takabatake et al .…”

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

“…This idea is supported both by the delayed determination of the notochord with respect to the onset of gastrulation, in urodeles compared with anurans (Kaneda and Suzuki, '83;Sakaguchi et al, 2002) and by the delayed onset of Brachyury expression in Cynops (Sone et al, '97;Yokota et al, '98;Tabata et al, 2001) and Ambystoma (Johnson et al, 2003) after the beginning of gastrulation, compared with its earlier expression in Xenopus (Smith et al,'91). Perhaps this reflects a more progressive mode of patterning, with only the currently more vegetal population of cells in the portion of the marginal zone that has not yet ingressed receiving signals for specification and cell behavior.…”

“…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.…”