Fig. 1. The location and nomenclature of blastomeres used in this study. (A) 16-cell embryo (Hirose and Jacobson, 1979). (B) 32-cell embryo
labeled with the nomenclature of Jacobson and Hirose (1981). (C) 32-cell embryo labeled with the nomenclature of Nakamura and Kishiyama
Fig. 2. Camera-lucida drawings of labeled surface cells (stippled),
members of clones of 16-cell blastomeres, at stage 7. Each clone
retains the shape and position of its progenitor blastomere, with
interdigitation of cells at the edge of the clone. (A) D1.1, animal
view, dorsal to the top. (B) D1.2, animal view, dorsal to the top.
(C) D2.1, vegetal view, dorsal to the top. (D) V2.1, view of ventral
midline, animal to the right.
Fig. 3. Camera-lucida drawings of labeled members of 16-cell clones
(stippled) in parasagittal (A), sagittal (B,D) and coronal (C) sections
of stage 7 embryos. (A) The D1.2 clone mixes with neighboring
clones by one or two cell diameters at the marginal zone edge.
(B) The D1.1 clone contains numerous unlabeled cells 3- to 6-cell
diameters from the edge of the clone. This is especially notable at the
animal cap border. (C) The D2.1 clone, viewed from just below the
floor of the blastocoel, mixes by one cell diameter with neighboring
clones at several sites. (D) The V2.1 clone barely interdigitates with
the clone of its lateral neighbor.
Fig. 6. Summary diagrams illustrating the locations of the clones derived from the midline
blastomeres of the 32-cell embryo (A) at stage 8 (B), stage 9 (C), stage 10 (D), stage 11
(E), and stage 12.5-13 (F). Data were derived from tissue sections in which two adjacent
blastomere clones were labeled with different lineage dyes. These illustrations are
composite summaries of at least three embryos per blastomere pair. Diagrams are oriented
as in Fig. 1. Clones are represented by the following colors: lilac, C4; orange, B4; green,
A4; yellow, A1; red, B1; blue, C1; purple, D1. Illustrations in B-F are based on
midsagittal photomicrographs by Hausen and Riebesell (1991).
Fig. 4. At stage 7, mixing of the D1.1 clone is primarily with its contralateral neighbor. One D1.1 blastomere was labeled with FDA (green),
the contralateral D1.1 blastomere was labeled with TRDA (red). Transverse section, dorsal is to the top. Bar equals 200 mm in all color
Fig. 5. At stage 8, descendants of A4 (red) were found one or two cell diameters on the dorsal side of the animal pole (line), while the animalmost
descendants of A1 (green) no longer reached the animal pole. Sagittal section, dorsal is to the right.
Fig. 7. At stage 9, the A4 clone (green) has moved into the dorsal part of the animal cap. Its deep cells underlie more superficial cells of the B4
clone (red) in the blastocoel roof. Sagittal section, dorsal is to the left, animal pole is marked by line.
Fig. 8. At stage 9 both the B1 clone (red) and the C1 clone (green) have moved into the vegetal marginal zone. A few descendants of C1 can be
found three or four cell diameters within the clone of B1. Parasagittal section, dorsal is to the right. Dotted line indicates level of the blastocoel.
Fig. 9. At stage 10, the A4 clone (green) has spread over most of the blastocoel roof. The B4 clone (red) extends from the animal cap to the
noninvoluting marginal zone (solid arrow), contributing some deep cells to the involuting mesoderm (open arrow). Sagittal section, dorsal is in
the lower right corner. Animal pole is marked by line.
Fig. 10. At stage 11, the clones of A1 (green) and B1 (red) are distinct in preinvolution mesoderm, but mix as they approach the site of
invagination (arrow) and enter the postinvolution mesoderm. Sagittal section, dorsal is to the top.
Fig. 11. At stage 10, the B1 clone (red) occupies the dorsal blastopore lip to the site of invagination (arrow). The C1 clone (green) stretches
from the yolk plug to the floor of the blastocoel.
Figs 12, 13. Two examples of stage 10 embryos in which the B1 clone (red) is the primary contributor to the marginal zone of the dorsal
blastopore lip, but members of the C1 clone (green) also make a small contribution. Arrows mark the site of invagination. Orientation is the
same as in Fig. 11.
Fig. 14. At stage 12.5, the A1 clone (green) has reached the blastopore lip (arrow) and contributes extensively to the entire neural ectoderm.
The B1 clone (red) extends throughout the anterior/posterior extent of both neural and mesodermal layers. a, anterior; p, posterior. Sagittal
section dorsal is to the top.
Fig. 15. At stage 12, the A4 clone (green) and the B4 clone (red) extend across the ventral epidermis from anterior (a) to posterior (p). The
ventral blastopore lip is at the upper left edge of the micrograph (arrow). The clones intermix extensively in the posterior half of the deep layer.
Sagittal section dorsal is to the top.
Fig. 16. Camera-lucida drawings of the positions of 16-cell clones in the vegetal hemisphere during gastrulation. In the top row clones of D2.2,
V2.1, D1.2, and V1.1 are shown. In the bottom row clones of D1.1, D2.1, V2.2, and V1.2 are shown. At stage 10 (left), the four vegetal clones
are in the positions of the original blastomeres. In addition D1.1 has moved from the animal hemisphere to form the dorsal lip of the blastopore
(bottom, stippled). Note that cells from the D2.2 clone form the lateral edge of the lip (top, stippled) and that a few cells from the D2.1 clone
are in the dorsal lip (bottom, white). At stage 11 (middle), the two lateral animal clones (D1.2, top; V1.2, bottom) have extended into the
vegetal hemisphere and reached the blastopore lip. The D1.1 clone has undergone convergent extension to become a narrow midline stripe. At
stage 12 (right), the dorsal clones have narrowed due to convergent extension and the ventral clones have spread over a larger surface area. A
small portion of the V1.1 clone (top, black) approaches the ventral lip at the midline, but does not involute.
Table 1. Positions of 16- and 32-cell clones in the stage 10 gastrula and their fates
The locations of the blastomere clones at stage 10 were described according to the regions defined by Keller (1975, 1976). The fates of these regions (Keller,
1975, 1976) and the observed phenotypes of the blastomeres clones in the tailbud embryo (Moody, 1987a,b) are compared. It should be noted that as a
consequence of mixing between clones, as described in the Results section, each clone also makes minor contributions to neighboring regions not listed in this