Journal of Neuroscience, Vol 11, 1990-1997, Copyright © 1991 by Society for Neuroscience
The regulation of transmitter expression in postembryonic lineages in the moth Manduca sexta. II. Role of cell lineage and birth order
JL Witten and JW Truman
Department of Zoology, University of Washington, Seattle 98195.
The expression of GABA is restricted to the progeny of only six of the 24
identified postembryonic lineages in the thoracic ganglia of the tobacco
hornworm, Manduca sexta (Witten and Truman, 1991). It is colocalized with a
peptide similar to molluscan small cardioactive peptide B (SCPB) in some of
the neurons in two of the six lineages. By combining chemical ablation of
the neuroblasts at specific larval stages with birth dating of the progeny,
we tested whether the expression of GABA and the SCPB-like peptide was
determined strictly by cell lineage or involved cellular interactions among
the members of individual clonal groups. Chemical ablation of the six
specific neuroblasts that produced the GABA-positive neurons (E, K, M, N,
T, and X) or of the two that produced the GABA + SCPB-like-immunoreactive
neurons (K, M) prior to the generation of their lineages resulted in the
loss of these immunoreactivities. These results suggest that regulation
between lineages did not occur. Ablation of the K and M neuroblasts after
they had produced a small portion of their lineages had no effect on the
expression of GABA, but did affect the pattern of the SCPB-like
immunoreactivity. Combining birth-dating techniques with transmitter
immunocytochemistry revealed that it was the position in the birth order
and not interactions among the clonally related neurons that influenced the
peptidergic phenotype. These results suggest that cell lineage is involved
in establishing the GABAergic phenotype and that both cell lineage and
birth order influence the determination of the peptidergic
phenotype.(ABSTRACT TRUNCATED AT 250 WORDS)