Figure 6. Vulval expression of a sur-2
::IacZ transgene. N2 hermaphrodites carrying an integrated sur-2
:lacZ translational fusion (kuls15( were fixed and stained with X-gal. (a) Late L1 larva. Many neurons stain in the ventral cord. These include the Pn.a and presumably the DB and DA neurons. The P(1-12).p cells also stain. (b) L3 larva. The Pn.p cells have divided to gen- erate Pn.pa and Pn.pp daughters that stain. From left to right, brackets indicate P5.pa and P5.pp, P6.pa and P6.pp, P7.pa and P7.pp, and P8.pa and P8.pp. The daughters of P3.p and P4.p also stain but are not within the field of the photomicrograph. (c) L3 larva; the Pn.pxx descendants of P5.p, P6.p, and P7.p stain. These cells will generate the normal vulva. The staining in the descendants of P3.p, P4.p, and P8.p at this stage is greatly reduced. (d) Late L3 larva. The arrow depicts the vulval invagination formed from the descendants of P5.p, P6.p, and P7.p. They no longer express the sur-2
:lacZ transgene. The strongly staining cell above the invagination is the anchor cell.