Homozygous Ark1 mutants exhibit delayed development (by about 2 days compared to controls). Approximately 70% of Ark1 mutants survive to early pupal stage compared to heterozygous controls.
Although larval and pupal tissue from Ark1 mutants appear grossly normal externally, some larval tissues derived from late third instar animals show hyperplasia. For example, the larval central nervous system is enlarged in Ark1 mutants. This is particularly evident in the ventral ganglion that appears to be elongated and contains longer nerve fibers. Approximately 40% of Ark1 mutants exhibit enlarged wing discs. In a smaller number of mutants, the eye discs are also enlarged.
Extra neurons in chordotonal cell clusters are observed in Ark1 mutant embryos. There are up to three extra cells per cluster in the majority of Ark1 mutant embryos. Gross morphological abnormalites in ventral nerve cord structure are also observed. For example, commissures can appear wider than in wild-type, and axons can appear more densely packed. In many animals, the ventral nerve cord can appear to be improperly compacted and the spacing between longitudinal axonal tracts is enlarged.
Apoptosis is almost absent (when compared to wild-type) in Ark1 mutant brain lobes, and is greatly reduced in win discs. Larval eye discs also display a dramatic decrease in the number of dying cells compared to wild-type. Caspase activity is also lower in Ark1 mutants.
Larval salivary gland removal is markedly delayed in Ark1 animals. They exhibit persistent or partially degraded salivary glands with an intact lumen at 20 hours relative to puparium formation at a time when, in wild-type animals, salivary glands have been completely removed. Indeed, intact salivary glands are still present at 30 hours relative to puparium formation. The persistent salivary glands are highly vacuolated. At the same time, adult structures, such as wings, are forming in Ark1 mutants, indicating continuing pupal development. No TUNEL-postive nuclei (indicating apoptosis) are observed in Ark1 mutant salivary glands at a time when wild-type glands are TUNEL-positive.
Midgut removal is largely normal in Ark1 animals, with morphological changes occurring as in wild-type, along with wild-type levels of apoptosis and caspase activity.
After irradiation with γ-rays, the basal number of Acridine Orange-positive cells (to monitor levels of apoptosis) in Ark1 animals is very low. In comparison, wild-type animals exhibit large increases in apoptosis in brain lobes, eye discs, and wing discs. However, no increase in apoptosis is observed in any tissue of Ark1 mutants, suggesting that these organs in Ark1 mutants are resistant to apoptosis induced by γ irradiation.