At the beginning of the third instar taenidial spacing in Mmp12 larvae does not differ from wild type.
Intertaenidial distance does not increase from early to late third instar in Mmp12 mutants whereas an approximately two fold increase in elongation occurs in controls. The lack of intertaenidial elongation compared to body length increase in Mmp12 mutant results in broken dorsal trunk trachea in 93% of third instar larvae.
Mmp12/Mmp1Q112stop mutants display similar taenidial spacing at the early third instar stage compared to controls but reduced intertaenidial distance compared to wild type by late third instar.
Mmp12 mutants have a reduced angle between the dorsal trunk and the transverse connective compared to wild type.
The intertaenidial distance in Mmp12 early second instar larvae is similar to wild type but the elongation that occurs between the early and late second instar in wild type does not take place in Mmp12 mutants.
The shedding of cuticle in the dorsal trunk that takes place in wild type prior to the third instar stage does not take place in a large proportion of Mmp12 mutants, with many larvae having two or three cuticles compared to one in controls.
When the inner cuticle breaks in wild type the break occurs in the vicinity of the fusion cells and disrupts their pattern, whereas 80% of the breaks seen in Mmp12 mutants are not in the vicinity of the fusion cells and the pattern is intact.
A separation between the cell and cuticular layers is seen in late third instar Mmp12 mutants that is not seen in wild type or in early third instar mutant larvae.
The ratio of apical membrane length to tracheal tube length is greater in Mmp12 late third instar larvae compared to controls indicating that the membrane elongates more than the matrix. However the length of the apical membrane is still reduced in Mmp12 mutants compared to wild type.
45% of Mmp12 mutant third instar larvae display broken tracheal dorsal trunks. None survive to pupariation.
44% of Mmp1Q112stop/Mmp12 transheterozygous mutant third instar larvae display broken tracheal dorsal trunks.
ISNb pathfinding in Mmp1Q112stop/Mmp12 embryos is roughly wild type, though 28% of hemisegments display a loosely fasciculated ISNb morphology. SNa fasciculation is also decreased.
90% of Mmp1W439stop/Mmp12 animals survive to third instar, but only 10% pupariate, 2% undergo head eversion, and none eclose. 87% of Mmp1Q273stop/Mmp12 animals survive to third instar, but only 22% pupariate, 6% undergo head eversion, and none eclose. Most Mmp1W208stop/Mmp12 animals survive to third instar (90%), but only 6% pupariate; 4% undergo head eversion, but none eclose. Most Mmp1Q112stop/Mmp12 animals survive to third instar (84%), but only 7% pupariate. All 7% undergo head eversion, but none eclose. Third instar Mmp12 mutant larvae frequently have breaks in the dorsal trunk and internalised posterior spiracles. The tracheal system phenotypes of Mmp1Q112stop/Mmp12 larvae get more severe with age: 1. First instar: in small first instars larval trachea do not have quite as much slack as those of controls. This defect is more apparent in larger first instar larvae, where the tracheal system is visibly stretched and has no slack, especially along the transverse connectives. 20% (n = 25) of have breaks in their dorsal trunks, presumably caused by overstretching. 2. Second instar: shortened dorsal trunks; the posterior spiracles have moved inward; 44% (n = 62) have visible breaks in the dorsal trunks. 3. Third instar: The tracheal system is stretched dramatically toward the anterior of the animal, with prominent tracheal breaks in 42% (n = 52) and posterior spiracles separated from the surface of the cuticle in all. Mmp1Q112stop/Mmp12 larvae are variable in size, but are always small than their wild-type siblings. Occasional Mmp12 mutant animals fail to shed their cuticles completely at the L2/L3 molt: The old mutant cuticle appears to remain attached at the mouthhooks and/or at a lateral spiracle through which tracheal cuticle is shed.