W530term | tkv-PA; W498term | tkv-PB; W542term | tkv-PC; W476term | tkv-PD
G to A nucleotide change at the second or third position of the wild type Trp codon leads to a nonsense mutation (exact site of mutation unspecified). The mutation was annotated at the second base of the codon.
24 hours after induction of tkv4, Df(2L)flp147E double mutant clones in the second instar larval stage, mutant wing disc cells show apical constriction and shortening along their apical-basal axis compared with neighbouring control cells. At 26-60 hours after clone induction, mutant cells are further shortened, and are part of a deep epithelial invagination. Mutant cells have normal apical-basal polarity. At 60 hours after clone induction, some mutant cells are confined to the basal portion of the epithelium, and these extruded mutant clones have an internal lumen. Other clones show extrusion and no internal lumen.
Expression of Cad86CScer\UAS.T:Ivir\HA1 under the control of Scer\GAL4Act5C.PP in smo3 tkv4 double homozygous clones in the region of the morphogenetic furrow can result in the formation of an epithelial invagination in some cases. Cells at the centre of this invagination are shorter along their apicobasal axis compared to smo3 tkv4 double homozygous clones or to wild-type cells within the morphogenetic furrow.
As tkv4 clones in the wing pouch do not survive due to apoptosis, and bskflp147E single mutant clones show no segregation defects in the wing, tkv4 bskflp147E clones can be used to study whether tkv4 affects segregation of cells at the A/P boundary. The majority of bskflp147E tkv4 clones of A origin in contact with the A/P boundary of the wing disc are misplaced into the P territory, causing a displacement of the A/P compartment boundary toward P. However, clones of P origin remain in the P compartment.
The frequency of recovery of tkv4 bskflp147E double mutant clones (induced during the first larval instar) in the wing disc pouch of late-third instar larvae is only 24% compared to sibling wild-type clones, probably due to the formation of cyst-like structures followed by extrusion from the basal side of the epithelium. The double mutant clones are shorter along their apical-basal axis than normal, have lost contact to the apical epithelial surface and form cyst-like structures with the apical cell membranes facing the centre of the clone instead of the disc lumen. F-actin is enriched at the centre of the double mutant clones, whereas a dense apical network of microtubules, which is present in wild-type cells, is markedly reduced. Basal microtubules appear normal. Some tkv4 bskflp147E double mutant clones are seen in adult wings, as extruded cyst-like structures located between the dorsal and ventral wing surfaces. These mutant cells display hairs, characteristic structures of the adult epithelium, indicating that the extruded cells have undergone differentiation.