XB-ART-28025Dev Biol August 1, 1987; 122 (2): 300-19.
Fates of the blastomeres of the 32-cell-stage Xenopus embryo.
A detailed fate map of all of the progeny derived from each of the blastomeres of the 32-cell-stage South African clawed frog embryo (Xenopus laevis), which were selected for stereotypic cleavages, is presented. Individual blastomeres were injected with horseradish peroxidase and all of their descendants in the late tailbud embryo (stages 32 to 34) were identified after histochemical processing of serial tissue sections and whole-mount preparations. The progeny of each blastomere were distributed characteristically, both in phenotype and location. Most organs were populated largely by the descendants of particular sets of blastomeres, the progeny of each often being restricted to defined spatial addresses. Thus, the descendants of any one blastomere were distinct and predictable when embryos were preselected for stereotypic cleavages. However, variations among embryos were common and the frequencies with which one may expect organs to contain progeny from any particular blastomere are reported. The differences in the fates of the 16-cell-stage blastomeres and their 32-cell-stage daughter blastomeres are outlined and can be grouped into three general categories. The two daughter cells may give rise to equal numbers of cells in a particular organ, one daughter cell may give rise to many more of the cells in an organ derived from the mother blastomere, or one daughter cell may give rise to all of the progeny in an organ derived from the mother blastomere. Thus, cell fates are segregated during cleavage stages in both symmetric and asymmetric manners, and the lineages exhibit a diversification mode (G. S. Stent, 1985, Philos. Trans R. Soc. London Ser. B 312, 3-19) of cell division.
PubMed ID: 3596014
Article link: Dev Biol
Grant support: NS20604 NINDS NIH HHS , NS23158 NINDS NIH HHS
Genes referenced: gan
Article Images: [+] show captions
|FIG. 1. The names of the blastomeres of the 32-cell-stage Xenopus embryo, as assigned by Jacobson and Hirose (1981). Although Xenopus embryos need not cleave in this pattern, those used in the present study all did.|
|FIG. 2. Stage 33/34 embryos in which a single 32-cell stage blastomere was injected with HRP. Blastomeres from different regions of the embryo (depicted in 2i) were chosen to illustrate the characteristic labeling patterns. The epidermis was removed and the entire embryo ￼histochemically reacted. Progeny of the injected blastomere are brown. Black melanocytes surround the retina, CNS, and dorsal gut; proctodeal and cement gland cells also contain melanin pigment granules. Therefore, these structures may appear pigmented even though they do not contain HRP-labeled progeny. The locations of the organs in the tailbud embryos are depicted in 2j. Bars equal 1 mm. (a) D1.2.1. Labeled progeny populate the cement gland, olfactory placode, retina, lens, cranial ganglia, otocyst, brain and spinal cord, dorsal head mesenchyme, branchial arches, heart, head somites, central trunk somites, ventral gut, and liver. Note how different the distribution of labeled cells is compared to that of a neighboring cell shown in 2e. (b) D1.1.2. Labeled progeny populate the retina, cranial ganglia, brain and spinal cord, dorsal head mesenchyme, branchial arches, heart, notochord, head somites, and central trunk somites. The progeny distribution is distinct from that of the other dorsal animal pole blastomere (2a) and very different from the other tier 2 blastomere (2f). (c) D2.1.1. Labeled progeny in this specimen populate one branchial arch, heart, liver, and gut. The distribution of its progeny is different from that of a neighbor cell in the same tier (Zd). (d) D2.2.1. Labeled progeny in this specimen populate spinal cord, trunk somites, nephrotome, lateral plate, and gut. Many of the labeled structures lie deep to other labeled structures and thus are not distinctly identifiable at the focal plane of the photomicrograph (e.g., spinal cord, archenteron roof, nephrotome). The distribution of the progeny of D2.2.1 is distinctly different from those of its two tier 4 neighbors (2~ and 2h). (e) V1.2.1. Labeled progeny in this specimen populate the cement gland, olfactory placode, lens, three distinct cranial ganglia (rostra1 to caudal: V, VII, IX/X), otocyst, dorsal brain, dorsal spinal cord, branchial arches, heart, a few cells in the trunk somites, nephrotome, rostra1 lateral plate, liver, and ventral gut. The distribution of its progeny is very different from that of its neighbor (2a) and from that of the other ventral animal pole blastomere (2f). (f) V1.1.2. Labeled progeny in this specimen populate caudal trunk and tail structures. Those that can be clearly identified in the photomicrograph are dorsal and ventral trunk somite, lateral plate mesoderm, ventral gut, and proctodeum. (g) V2.2.2. Labeled progeny in this specimen populate cranial ganglia, otocyst, dorsal CNS, dorsal head mesenchyme, branchial arches, somites, nephrotome, lateral plate, gut, and proctodeum. The distribution of its progeny is distinct from that of its sister cell (2h). (h) Labeled progeny in this specimen can most clearly be identified in ventral tail somite, nephrotome, lateral plate, gut, and proctodeum.|
|FIG 2 ( continued) (i) A diagram of the 32-cell-stage embryo, in the same orientation as that in Fig. 1, illustrating the position of the blastomeres that were injected to produce the embryos displayed in Figures 2a-2h. The four animal pole blastomeres often are called tier 1, the four blastomeres posterior to those tier 2, the four blastomeres posterior to those tier 3 and the four vegetal pole blastomeres tier 4. (j) A diagram of a stage 33/34 tailbud embryo in which the structures containing labeled cells in the preceding photomicrographs have been identified. Since many of these structures overlap, or are composed of very small cells, they may not be distinct at the focal plane or magnification of the photomicrograph. b, branchial arches; cg, cement gland; cr gan, cranial ganglia. Rostra1 to caudal these are trigeminal, facioacoustic, glosso- pharyngeal-vagal; dcv, dorsal, central, and ventral trunk somites. These extend rostrally, deep to the otocyst, where they are considered to be head somites; h, heart, 1, lens; ne, nephrotome. This structure extends caudally, deep to the ventral somite; no, notochord. This structure extends caudally to the tailbud (tb) and its cells are seen as vertical rods (as diagrammed); op, olfactory placode; ot, otocyst; pr, proctodeum; sp cd, spinal cord. This structure extends caudally to the tailbud (tb). Dorsal head mesenchyme is that tissue in the head, dorsal to the hranchial arches, that lies between the structures labeled in this diagram.|