ina-1 mutants were originally isolated in a screen for mutants with HSN migration defects, but display widespread defects in cell motility and morphogenesis.
ina-1 mutants also exhibit defects in the migrations of the CANs, ALMs, Q neuroblasts, distal tip cells and coelomocyte mother cells. Anti-GABA staining revealed mild fasciculation defects in
ina-1 ventral nerve cords. The heads of
ina-1 animals develop a ventral notch after embryonic elongation, and weak alleles of
ina-1 (
gm39 and
gm119), which are often viable and fertile, exhibit defects in vulval and uterine morphogenesis. Strong alleles of
ina-1 (
gm86 and
gm88) arrest as L1s due to starvation; their pharynxes are misshapen and unable to pump normally.
ina-1 maps to chromosome III, between
lin-12 and
ced-7. Mutants can be rescued by the F54G8.3 alpha integrin gene. Mutations have been found in the coding region of this gene in three out of four alleles.
gm86 is an opal nonsense mutation in the extracellular domain suggesting that it is a null allele. Antibodies have been raised to a peptide from the cytoplasmic domain of INA-1. These antisera stain the pharynx in N2 embryos but not
ina-1(
gm86) mutants. Because these antisera stain N2 animals very faintly compared to those carrying overexpressing arrays, the integrin may normally be expressed outside the pharynx at levels too low for the antisera to detect. As an alternative to antibodies, a tagged construct was made which contains 15 kb of the
ina-1 genomic region modified only by a GFP insertion just before the stop codon. This construct is able to fully rescue
gm86 mutants. The integrated transgene shows a dynamic pattern of expression consistent with the many phenotypes of
ina-1 mutants.
ina-1::GFP is first expressed ubiquitously in embryos during morphogenesis. Beginning at comma stage, the transgene is more intensely expressed in the pharynx and scattered other cells. In larvae and adults, GFP expression remains in the pharynx. In addition, there is expression in various head and tail sensory neurons, as well as in lateral and ventral nerve cord neurons. The migrating Q cells and distal tip cells show intense GFP expression, and expression is seen in the developing uterus and vulva as well. Because the
ina-1 expression pattern appears to overlap with that reported for the beta integrin
pat-3 (1), and mutations in each integrin disrupt many of the same cell migrations (2), it is likely that the two subunits dimerize. This possibility is being tested directly. Mosaic analysis is in progress to determine if
ina-1 functions cell-autonomously in cell migrations and whether the notched head is a result of hypodermal or muscle defects. Finally, pharyngeal sections of
gm86 mutants are being examined by electron microscopy to identify possible ultrastructural correlates of the animals' pumping defect. (1) S.N. Gettner, C. Kenyon and L. F. Reichardt, (1995) Journal of Cell Biology 129: 1127-1141. X. Zhu and E. Hedgecock, 1995 International Worm Meeting abstract number 567. (2) M. Buechner and E. Hedgecock, (1992) Worm Breeder's Gazette 12(3): 97.