Novel EMS-induced LanB1 alleles associated with alary muscle detachment and abnormal dorsal vessel morphology. Live stage 16–17 wild-type (S-18a-13b-16b.1 control) or LanB1 mutant embryos (dorso-lateral views) carrying tinC*-GFP, org-1-SM-RFP, and HLH54F-LVM-RFP to monitor the morphology of the dorsal vessel (DV), alary muscles (AM) and longitudinal visceral muscles (LVM), respectively. tinC*-GFP is visible in all cardiomyocytes and weakly in some pericardial cells. RFP is also present in somatic muscles 5, 8 and 25 (partially in focus; M5, M8, M25), and in additional thoracic muscles. Embryos in D-F also carry Mhc-tau::GFP for the visualization of the entire musculature (single RFP channel on the right). (A) In the wild type, seven pairs of AMs connect to the DV. A pair of anterior longitudinal muscles (thoracic alary-related muscle, T) connects to the midgut. (B) Homozygous LanB1S0733 embryo in which the AMs have begun to separate from the DV or are already completely detached (arrows). The DV has retracted from the posterior end (arrowhead). The LVM and thoracic alary-related muscle attachment appear mostly normal. (C) Strong alleles such as LanB1S0464 (here over the LanB1-deleting deficiency Df(2L)ED12527) show a more pleiotropic phenotype, in which the midgut (*) lacks constrictions and is only partially associated with visceral musculature. Severe heart defects such as gaps (large arrowhead) are more frequent than in LanB1S0733. (D, D′) Control embryo with additional Mhc-tau::GFP showing the wild-type muscle pattern. (E, E′) LanB1S0733/Df(2L)ED12527 embryo. The body wall musculature shows only minor detachment or loss of a few fibers (small arrowhead) while most AMs are already detached at this time point (arrows). (F, F′) Amorphic LanB1S0473 allele over Df(2L)ED12527. In addition to AMs many fibers of the body wall musculature detach resulting in an irregular shape or gaps (small arrowheads). Furthermore the visceral musculature fails to surround the unconstricted ball-shaped midgut.