Rr. Dubreuil et al., MUTATIONS OF ALPHA-SPECTRIN AND LABIAL BLOCK CUPROPHILIC CELL-DIFFERENTIATION AND ACID-SECRETION IN THE MIDDLE MIDGUT OF DROSOPHILA LARVAE, Developmental biology, 194(1), 1998, pp. 1-11
Mutations in Drosophila alpha spectrin cause larval lethality and defe
cts in cell shape and adhesion (J. Lee et al., 1993, J. Cell Biol. 123
, 1797-1809). Here we examined the effects of two lethal alpha spectri
n alleles (alpha-spec(rg41) and alpha.spec(rg35)) on development and f
unction of the larval midgut. Homozygous null alpha-spec(rg41)-mutant
larvae exhibited a striking defect in middle midgut acidification. In
contrast, many homozygous alpha.spec(rg35) mutants were capable of aci
dification, indicating partial function of the truncated alpha-spec(rg
35) product. Acidification was also blocked by a mutation in the labia
l gene, which is required for differentiation of cuprophilic cells in
the midgut, suggesting that these cells secrete acid. We found that tw
o isoforms of spectrin (alpha beta and alpha beta(H)) are segregated w
ithin the basolateral and apical domains of cuprophilic cells, respect
ively. The most conspicuous defect in cuprophilic cells from labial an
d alpha spectrin mutants was in morphogenesis of the invaginated apica
l domain, although basolateral defects may also contribute to the acid
ification phenotype. Acid secretion in vertebrate systems is thought t
o involve the polarized activities of apical proton pumps and basolate
ral anion exchangers, both of which interact with spectrin. We propose
that the alpha-spe(rg41) mutation in Drosophila interferes with the p
olarized activities of homologous molecules that drive acid secretion
in cuprophilic cells. (C) 1998 Academic Press.