In six comma-stage embryos, an average of 80.5 ( 2.5 s.d.) PHA-4-staining pharyngeal nuclei were counted by confocal microscopy (maximum count = 85). Analysis of later stage animals shows clearly that all six cells of the pharyngeal-intestinal valve contain PHA-4 protein. Thus the total number of potentially staining nuclei (pharynx + valve) should be equal to 86. all cells of the pharyngeal primordium (+ valve) contain the nuclear factor PHA-4. The same embryos also show nuclear PHA-4 in 6-8 rectal cells, including the two rectal valve cells and the three rectal epithelial cells. At the lima bean and comma stages of embryogenesis, a low but significant level of PHA-4 can be detected in the gut. pha-4
gene is expressed in pharyngeal precursor cells well before the formation of the pharynx primordium. PHA-4 can be detected immunologically in most but not all nuclei of the larval and adult pharynx. PHA-4 is detected in nuclei of all epithelial cells, muscle cells, marginal cells, gland cells and pharyngeal intestinal valve cells, but is detected only in about 8 of 19 neuronal nuclei. PHA-4 is also detected in one (comma stage) to several (pretzel stage and later) head cells outside of the pharynx. PHA-4 can also be detected in nuclei of the developing somatic gonad, including the distal tip cell and ventral uterine cells.