is symmetrically expressed between the two Q neuroblasts. This expression is however transient and restricted to the time period in which the initial polarization and migration of the Q neuroblasts takes place. Thus, within the first two hours after hatching, when the Q neuroblasts have polarized but the cell body has not yet migrated, an average of 25 4.6 mig-21
transcripts (mean SD, n = 12) were found in QL and 26 5.0 transcripts in QR (n = 17). At 2-4 h after hatching, when the Q neuroblasts are migrating over their neighboring seam cells, expression decreased slightly, with 17 5.8 mig-21
transcripts in QL (n = 15) and 21 6.2 transcripts in QR (n=18). Four to six hours after hatching, when the Q neuroblasts have divided, mig-21
expression was strongly decreased, with 2 2.4 transcripts in QL (n = 22) and 5 3.4 transcripts in QR (n=19). In addition to the expression in the Q neuroblasts, mig-21
is also expressed in the four body wall muscle quadrants of L1 stage larvae. In contrast to the expression in the Q neuroblasts, the muscle specific expression of mig-21
persists throughout development.