Fig. 4. SPON-1 is required for late elongation and interacts with INA-1 -integrin. (A-P) Frames from time-lapse analysis of wild type (A-D), spon-1(ju402) mutants (E-H), putative ina-1(gm144); spon-1(ju430)/+ mutants (I-L) and spon-1 ina-1 double mutants (M-P). Most spon-1(ju402) embryos developed normally up to either 2- or 3-fold stage (F,G), but then retracted to 2.5-fold (H) by the time the wild-type embryo has developed to the 3-fold stage (D). spon-1(ju402) embryos displayed normal muscle twitching movements from 1.75- to 3-fold stage before elongation arrest (see Movie 1 in the supplementary material). Body constrictions became apparent when muscle movements slowed down and later stopped. At the restrictive temperature, spon-1(ju430ts) mutants resemble ju402 in phenotype. More spon-1(ju402) embryos retracted to a 2-fold stage (12/19, 63%) than did spon-1(ju430ts) embryos (7/33, 21%). Sixty-three percent of spon-1(ju402) and 79% of spon-1(ju430ts) embryos reached the 3-fold stage before retraction. spon-1(ju348) embryos were indistinguishable from ju402 in embryonic phenotype. ina-1(gm144) mutants displayed normal elongation (not shown). (I-L) From strains of genotype ina-1(gm144); spon-1(ju430)/mIn1 mIs14 mutants, 41% (18/44) GFP-positive embryos (either ina-1;spon-1/mIn1 mIs14 or ina-1; mIn1 mIs14) displayed late-onset elongation defects. No ina-1 mIn1 mIs14 embryos (n=11) showed elongation defects. We infer that 60% of spon-1/+ heterozygotes have elongation defects in the gm144 background. Six out of seven ju430; gm144 homozygotes (GFP-negative embryos) displayed 1.5-fold arrest (M-P). (Q) Early elongation rates (mean±s.e.m.). spon-1 mutants elongate normally from comma to 2-fold stage, emb-9 mutants were slightly slower, pat-3 mutants were significantly slower (^**P<0.05, ANOVA). (R) The spon-1(ju430ts) temperature-sensitive period begins at the 2-fold stage.