Caactg Gttgac

100 bp

HrMAIa r*

HrMHCI

FIGURE 3.5 Autonomous specification of mesodermal precursors in asci-dian eggs. (A) Partial B4.1 half lineage (i.e., lineage of one side of the bilaterally symmetrical embryo) displaying origins of primary tail muscle cells and of mesenchyme cells. Color coding is as in Fig. 3.4A, i.e., red, muscle; yellow, endoderm; light green, mesenchyme. The geometry of the 8-cell embryo, including the B4.I cell pair, viewed from the side (anterior right, vegetal down) can be seen in (E5). The lineage is from Halocynthia roretzi (Satoh, 1994; Satou et al., 1995), but the portion shown is the same for Ciona intestinalis. Muscle and mesenchyme are mesodermal cell types. Not shown are some minor additional contributions: B7.5 produces adult muscle precursors (dashed red line) as well as two tail muscle cells. Also, note that a descendant of B7.3, viz, B8.6, produces four notochord cells on each side (black dashed line), while its sister cell, B8.5, produces mesenchyme. (Most notochord cells, 16 on each side, derive

FIGURE 3.5 (Continued)

FIGURE 3.5 (Continued)

TbxG

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