a = anterior an = animal bc = blastocoel bp = blastopore d = dorsal dl = dorsal lip dm = deep mesoderm fg = foregut fp = floor plate hg = hindgut l = left no = notochord ov = otic vesicle p = posterior r = right s = somite v = ventral veg = vegetal. (E’,E”) Histological sections (levels indicated in (E)) highlighting expression in the otic vesicle (E’) and nephrostomes ((E”), arrowheads). (E) Staining in the otic vesicle and nephrostomes (arrowheads). It is at this point that a distinction is made between the dorsal and ventral sides of the neural tube. Enlargements show multiciliated skin cells ( (D”) cilia indicated by arrowheads) and GRP cells after intercalation into the notochord ( (D”’) arrowheads). (D) Expression at stage 23 in ciliated cells of the epidermis and the floor plate (sagittal section shown in (D’)). The inductive properties of the dorsal blastopore lip change during gastrulation Dorsal lip grafts at the early gastrula stage produce a complete 2nd axis, while gra fts from late gastrula stage produce only a partial 2nd axis that lacks a head. The grafted tissue was taken from the dorsal lip of the blastopore (the slit-like invagination that forms where gastrulation begins on the dorsal surface of the amphibian embryo) from a color less (unpigmented) Triton Cristatus and implanted it onto a deeply pigmented Triton Taeniatus. (C’) Histological section (plane marked in (C)). (C) Expression in the gastrocoel roof plate (GRP) at stage 17 (dorsal explant shown in ventral view). Note that the superficial mesoderm (SM) was free of PACRG mRNA (inset in (B’)). (B’) Sagittal hemisection (plane indicated in (B)) revealing mRNA localization in deep mesoderm. Persistent differences in staining intensities between dorsal and ventral side. Enlargements (boxes) indicate higher expression levels on the dorsal side. (A’) Sagittal hemisection of embryo shown in (A). ![]() (A) Expression at the four-cell stage (top view). PACRG expression during early Xenopus development.
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