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Fig. 4. Muscle phenotypes of Poxm and l(1)sc mutants. (A-I) Muscle phenotypes resulting from loss of, or ectopic, Poxm. Dorsal (A-C), lateral (D-F) and ventral (G-I) muscles were visualized using an anti-MHC antiserum in three abdominal hemisegments of stage 16 wild-type (A,D,G), Poxm^R361 (B,E,H), and 24BGal4/UAS-Poxm (C,F,I) embryos, oriented with anterior to the left and dorsal up. In Poxm^R361 mutants, positions of missing muscles DT1 (white arrowheads) or an abnormal muscle DT1 (^*) and of a missing muscle DO3 (black arrowhead) are indicated in E, ventral muscles VO4-6 are missing (H), and ventral muscles VA1-3^* have lost their normal shape and attachments (H), as evident from a comparison with the wild-type ventral muscle pattern (G). Muscle VL4 is also frequently absent, as evident from inspection of a plane of focus interior to and below that shown in H. A detailed analysis of the Poxm^R361 muscle phenotype is summarized in Fig. 5A. Ectopic ubiquitous mesodermal expression of Poxm (C,F,I) generates ectopic dorsal and lateral muscles (marked by asterisks in F) and enlarges some ventral muscles (arrows in I), the number and positions of which are not altered. (J) Schematic external view (dorsal up and anterior to the left) of larval muscles in abdominal segments A2-A7 (Ruiz-Gómez et al., 1997), with external muscles in red and more internal muscles in blue and yellow; muscles are designated and numbered according to Bate (Bate, 1993) and in parentheses according to Crossley (Crossley, 1978). (K-M) Muscle phenotypes of Poxm mutants rescued by early Poxm, and of l(1)sc; Poxm double and l(1)sc single mutants. Muscle phenotypes were visualized using an anti-MHC antiserum in three abdominal hemisegments of Poxm^R361 embryos rescued by two copies of the um1-2-Poxm transgene (K), of Df(1)sc¹⁹ embryos (L), and of Df(1)sc¹⁹; Poxm^R361 embryos (M) at stage 16. Anterior is to the left and dorsal up. A detailed analysis of these phenotypes is summarized in Fig. 5B-D. Some muscles that are abnormal in shape and/or position are marked by asterisks, duplicated muscles DT1 (K) and DO3 (M) are labeled, and missing muscles VT1 (L), DT1 and LO1 (M) are indicated by black arrowheads. Ventral muscles VO4-6 that are missing in nearly all segments of Poxm single or double mutants (Fig. 5A,D) are also absent but not marked (M). (N) Schematic internal view of a hemisegment opposite to that shown in J (Ruiz-Gómez et al., 1997) of the muscle phenotype attributable to the absence of the early Poxm function, in which each muscle is colored in a graded fashion from red (0%) to yellow (100%) corresponding to the fraction of normal muscles observed (Fig. 5A). Muscles DO3, DT1 and VA1-3 are not colored as the contribution to their phenotype of the missing early Poxm cannot be estimated because they are also affected by the late Poxm function, and muscle VO3 is not colored because it has not been recorded in Fig. 5A.

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