pCZ178 and pCZ179 were expressed in similar sets of cells, however, GFP expression from pCZ178 was much weaker than from pCZ179 in most cells. CND-1::GFP expression was first detectable in four descendants of the AB lineage of 14 cell embryos. AB derived neuroblasts give rise to most of the C. elegans nervous system. By the 24-cell stage, approximately 75 minutes postfertilization, CND-1::GFP was found in 15 AB derived blastomeres. CND-1::GFP expression was observed in numerous unidentified nuclei throughout gastrulation and epidermal enclosure. By early comma stage, approximately 360 minutes postfertilization, CND-1::GFP was found in many postmitotic neurons in the head and in the ventral cord. The expression of CND-1::GFP in the ventral cord neurons was maintained until hatching, but disappeared completely by the end of the first larval stage. CND-1::GFP was not observed in postembryonically derived motor neurons. To determine whether
cnd-1 was expressed in non-neuronal cells of the AB lineage, embryos carrying
cnd-1::GFP transgenes were double labeled with anti-GFP and anti-LIN-26 antibodies. In all embryonic stages examined the expression of CND-1::GFP and LIN-26 did not overlap. To confirm the identity of specific AB-derived blastomeres during later stage embryogenesis, embryos carrying CND-1::GFP transgenes were double labeled with anti-GFP and anti-UNC-86 antibodies. CND-1::GFP and UNC-86 are primarily expressed in different subsets of mitotic and postmitotic neurons throughout embryogenesis. At 230 minutes postfertilization, UNC-86 is expressed in ABplaaaaaa, ABarpapaaa, ABplapaaaa, ABprapaaaa, ABarppaaap, and ABarpppapp blastomeres (Finney and Ruvkun, 1990). At the same stage, CND-1::GFP was found in a non-overlapping set of neuroblasts derived from the ABplppap and ABprppap, including ABplppaap, ABplppapp, ABplpppaa, ABprppapa, ABprppaap, ABprppapp and ABprpppaa, which give rise to the embryonic ventral cord motor neurons. In summary, reporter transgene analysis reveals that CND-1::GFP is expressed in both mitotically active neuroblasts throughout embryogenesis, and in subsets of postmitotic neurons including the ventral cord motor neurons.