Expr2974

For exact orientation, embryos were subjected to double staining by fluorescence in situ hybridization for the tbx-9 mRNA along with marker mRNAs. Two of the tbx-9 expressing cells were identified as the Ca and Cp cells. Double staining by fluorescence in situ hybridization for tbx-9 and elt-1 revealed the remaining three tbx-9 expressing cells were AB descendant cells destined for hypodermal cells.

Expr698

High levels in P2 and EMS (posterior nuclei) at the 4-cell stage. From 4-cell to the 24-cell stage, PAL-1 is detected in all descendants of both P2 and EMS. The PAL-1 antibody stained the nuclei throughout the cell cycle and was localized to the condensed chromosomes during mitosis. At the 24-cell stage, the level of staining intensity increased in the two C descendants, Ca and Cp. In 28-cell embryos strong staining was observed in the four C descendants and lower levels of staining was also observed in D and P4. At the 28-cell stage expression was stronger in P2 than in EMS descendants.

Expr841

PAL-1 produced from zygotic transcripts is seen initially in C and D lineage cells that also expressed maternally derived PAL-1. As gastrulation begins, expression is seen in only Ca and Cp and then in their daughters, of which 2 are hypodermoblasts (Caa and Cpa) and 2 are myoblasts (Cap and Cpp). The GFP reporter is first detected at the late 2C-cell stage and then more strongly in the 4 daughters. At about 100 cells, expression is also detected in the 2 D-lineage myoblasts. Thereafter, PAL-1 continues to be detected in all C and D descendants until the end of gastrulation at about 350 cells. At about 180 cells (midgastrulation), the C hypodermal precursors, which express more strongly than the muscle precursors, form a characteristic double row on each side of the dorsal midline in the posterior. Thereafter, PAL-1 decreases in these cells and is no longer detectable with antibody after 350 500 cells. At about 250 cells, expression is detected in two AB cells that border the posterior left edge of the mesectodermal cell layer that is closing the ventral gastrulation cleft (ABplpappp and ABplppppp) and slightly later in the right homolog of one of them (ABprppppp). The daughters and granddaughters of these cells, generated after the cleft closes, continue to express strongly along the ventral midline until about the time of hatching. Beginning at about 360 cells, as morphogenesis begins, weak transient expression is detected in the posterior ectodermal P cells and occasionally in posterior V cells as both groups move ventrally. During this period the V cells become the lateral seam cells, and the P cells undergo their terminal embryonic divisions as they complete hypodermal enclosure of the embryo. Meanwhile, in the interior, pal-1 expression, detectable both with antibody and with reporter constructs, appears at about 350 cells in 2 Ea descendents near the middle of the gut primordium (the int5 pair) and in 2 anteriorly located MS descendants which migrate to the posterior and become the mesoblast M and the right intestinal muscle (mu intR). During early morphogenesis as the embryo develops through the comma stage and begins to elongate, all the pal-1-expressing cells (approximately 50) are located in the posterior ventral region, except for the 2 midgut cells which lie more dorsally. The descendants of ABpl/rppppp, as well as mu intR, move into the elongating tail and participate in formation of the rectal and associated intestinal muscles, as well as the ventral tail hypodermis. Expression diminishes during elongation and by hatching is detectable only in the 2 gut cells, M, mu intR, and 10 cells descended from ABpl/rppppp.