Nucleotide substitution: C?T.
The C to T nucleotide substitution results in the truncation of the protein after residue 660.
C17023903T
C?T
Q662term | Dark-PB
?661term
Site of mutation estimated based on the reported location as a C to T mutation, causing protein truncation after residue 660.
3.1 +/ 1.2 surviving EW3-sib cells are seen in homozygous larvae (these cells die during embryogenesis in wild type).
Approximately 80% of Ark2 mutants survive to early pupal stage compared to heterozygous controls.
Although larval and pupal tissue from Ark2 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 Ark2 mutants. This is particularly evident in the ventral ganglion that appears to be elongated and contains longer nerve fibers. The majority of Ark2 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 Ark2 mutant embryos. There are up to three extra cells per cluster in the majority of Ark2 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 Ark2 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 Ark2 mutants.
Larval salivary gland removal is markedly delayed in Ark2 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 Ark2 mutants, indicating continuing pupal development. No TUNEL-postive nuclei (indicating apoptosis) are observed in Ark2 mutant salivary glands at a time when wild-type glands are TUNEL-positive.
Midgut removal is largely normal in Ark2 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 Ark2 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 Ark2 mutants, suggesting that these organs in Ark2 mutants are resistant to apoptosis induced by γ irradiation.
