Subject: P{GawB}17A expression
Enhancer trap expression of P{GawB}17A in the cardia
Kevin Cook and Robert Eisman
Indiana University
When P{GawB}17A was combined with various UAS-GFP reporter constructs,
intense fluorescence was observed in a band of cells around the cardia
(proventriculus) in addition to the expression previously reported in glial
cells and larval salivary glands. The cells expressing GAL4 in adult flies
corresponded to the region of the cardia described as Zone 5 by David King
in his article 'Cellular organization and peritrophic membrane formation in
the cardia (proventriculus) of Drosophila melanogaster' (J. Morph. 196:
253-282, 1988; FBrf0048518). According to King, Zone 5 is a region of
columnar epithelial cells responsible for secreting the third layer of the
peritrophic membrane. Fluorescence was also observed in a band around the
cardia in third instar larvae, but the position of the band was slightly
more posterior than in adults. We suspect that the shape of the cardia
changes during metamorphosis to bring zone 5 more anterior by further
involution of the midgut at the hilus of the cardia, but we did not examine
P{GawB}17A expression during pupal stages to confirm this. We also noted
expression in adult salivary glands.