Homozygous embryos have a wild-type muscle pattern.
WASp3 double mutant clones in the adult thorax exhibit external sensory cell loss and an excess of neurons.
Only 14% of actin foci in embryos maternally and zygotically mutant for WASp3 invade into founder cells, compared to 35% in wild type. The depth of invasion is also reduced.
Within WASp3 pIIa-pIIb cells, an apical actin-rich structure (ARS) is formed as in wild type, but its apical area is markedly reduced and, in about 50% of cases, the stalk of the normal 'umbrella shape' is not formed properly.
Homozygous embryos derived from females carrying homozygous germline clones show severe myoblast fusion defects.
WASp3 mutants exhibit muscle attachment defects but do not display unfused myoblasts.
WASp3D3-035/WASp3 transheterozygotes exhibit a myoblast fusion phenotype.
The cuticles of WASp3 mutants have abnormally thin denticles, which often display bent extremities.
WASp3/Df(3R)3450 mutants show a frequent loss of dorsocentral and scutellar bristles. The notopleural bristles are missing. They also show loss of microchaetae.
WASp1/WASp3 transheterozygotes survive to pharate adults. In these flies, many rhabdomeres do not obtain the normal characteristic oval shape, but rather are pointed and squared, with 2-3% of the mutant rhabdomeres split. The same phenotypes are seen in WASp3 homozygous somatic clones. In these clones F-actin accumulation along the photoreceptor apical surface is delayed and disorganised. At 48 hours there are regions of the photoreceptor cell in which the apical surface has not expanded and/or primordial microvillar projections have not formed. These regions are characterised by little or no F-actin enrichment compared with neighbouring wild-type cells. Ultrastructural analysis at this stage reveals loss of adherens junctions between mutant photoreceptors, no separation or elimination of cell-cell contacts between photoreceptor cells and a lack of primordial microvillar projections. While the initiation of rhabdomere microvilli formation is delayed, WASp3 mutant photoreceptor cells do form microvilli with an actin cytoskeleton core. At 72 hours, the developing mutant rhabdomeres are smaller in size or malformed compared with wild-type.
Syncytial blastoderm stage WASp3 germ-line clone embryos have wild-type nuclear morphology and distribution during nuclear division cycles 12-14. There are also no obvious cytoskeletal defects in mutants at these stages. In WASp3/Df(3R)3450 embryos from WASp3 germ-line clone carrying mothers, axon bundles in the ventral nerve cord appear thicker and defasciculated. Most of these embryos contain one to two segments with axon bundles collapsed at the midline (73% of embryos, n = 41). WASp3 mutant germ-lines undergo normal oogenesis and nurse cell development.
Hemizygotes complete nearly all stages of imaginal development and die as young adults, most commonly failing to eclose from the pupal case. Those that eclose can survive for a few days, but are lethargic and passive in their behaviour. WASp3/Df(3R)3450 embryos derived from WASp3 homozygous female germline clones do not survive. Embryos derived from WASp3 homozygous female germline clones with a wild-type paternal contribution of WASp develop normally, giving rise to viable and fertile adults. WASp3/Df(3R)3450 embryos derived from WASp3 homozygous female germline clones have normal cuticles. The initial selection of sensory organ determination appears to occur normally in these embryos, but they have an excess of neurons (a near doubling of normal numbers) in the mature peripheral nervous system (PNS). A corresponding reduction in the number of PNS nonneuronal support cells is seen; the number of cells expressing shaft and socket cell markers is reduced, although only mild effects on sheath cell numbers are seen. RP2 neuroblasts are duplicated. The mitotic spindles in the notum of WASp3/Df(3R)3450 pupae are positioned within the plane of the epithelium and along the anterior-posterior axis of the fly, as in wild type. The pI division in the lineage of the thoracic microchaetae is normal in WASp3/Df(3R)3450 pupae. However, subsequent events in the differentiation of this sensory organ lineage differ substantially from wild type. Either of the two pI daughter cells may divide after pI (in wild type the anterior pIIb cell always divides before the posterior pIIa cell) and the divisions of both of the pI daughter cells are morphologically identical and resemble the pattern seen in wild-type pIIb cells (both cell divisions are nonplanar and generate two daughter cells of different sizes).