Adult Dl6B mutants reared at 29[o]C display wing vein thickening and vein deltas.
Culturing Dl6B/DlRF animals at 18[o]C until the early second instar and then shifting to 25[o]C allows some animals to survive to the late third instar. These late third instar larvae have either no lamina or a very incomplete lamina, and have a smaller medulla complex than normal. At the late second-instar, these animals have a relatively normal neuroepithelium in the outer proliferation center, however, the neuroepithelial cells are partially lost by the mid-third instar. Medulla neuroblasts are generated prematurely during early to mid-third instar in these animals, leading to premature medulla neurogenesis (very few medulla neuroblasts are seen at the late-third instar).
In Dl6B/DlRF flies at the permissive temperature of `8[o]C, border cells migrate to reach the oocyte at stage 10. Following incubation of Dl6B/DlRF flies at the non-permissive temperature of 32[o][C overnight, border cells fail to migrate in 12 out of 72 stages 10 egg chambers examined, even though the clusters form.
The temperature sensitive heterozygous combination, Dlvi1/Dl6B leads to animals that exhibit a ISNb axon bypass phenotype. These axons reach their targets via an aberrant trajectory, in which ISNb axons remain associated with the ISN. About 23% of hemisegments are affected. The formation of neuromuscular synapses to ventral longitudinal muscles occur as efficiently in mutant animals than in controls. Other kinds of ISNb misrouting phenotypes are seen at a low frequency. However gross stalling of ISNb axons is not seen, nor are defects in muscle development.
Mild rough eye phenotype.
Heterozygotes show ectopic wing veins.
DlRF/Dl6B animals exposed to the restrictive temperature during the third larval instar and pupal periods develop shortened legs. The tarsal segments are particularly reduced and have seemingly disappeared, but the tarsal apical bristles are still present, and sometimes remnants of joint structures are also visible.
The number of esg-positive cells at the tip of the dorsal branch in the tracheal system is increased compared to wild type.
Abnormal microtubule organisation is seen in Dlvi1/Dl6B oocytes.
Homozygous clones including dorsal and ventral clones cause extensive wing scalloping. Clones in the ventral compartment cause small nicks or loss of margin sensory elements. Clones in the dorsal compartment cause only loss of sensory elements.
Clusters of R8 cells develop in DlRF/Dl6B flies raised at the restrictive temperature. The clusters are not randomly arranged, but are based on the original R8 array. Extra R8 cells are produced in Nl1N-ts1 DlRF/Dl6B double mutants, although the number of extra R8 cells produced is somewhat reduced compared to Nl1N-ts1 single mutants.
Dl6B/DlRF flies show a temperature-sensitive phenotype. At 18oC (permissive temperature) flies have a mild delta phenotype. Dl6B/DlRF larvae raised at 32oC for 5 hours give rise to eye discs with clusters containing extra cells compared to wild-type. These extra cells develop as photoreceptors. Adult flies derived from Dl6B/DlRF larvae heat pulsed 24 hours before puparium formation have a dorsal-ventral 'scar' on the eye, at the approximate position of the furrow during the heat pulse. This region contains a disorganised array of rhabdomeres, many of which are fused or misshapen. Extensive multiplication of cone cells is also seen in this region. Posterior to the scar, clusters contain excess outer photoreceptors and mild multiplication of cone cells is also seen. Posterior to this region, there is a narrow band of cone cell loss, and clusters contain the correct number and type of photoreceptors. The latticework in eye discs of Dl6B/DlRF pupae heat pulse from 11-18 hours after puparium formation (APF) appears to be composed almost entirely of bristles, with a loss of tertiary and secondary pigment cells. This gives rise to adult flies with rough eyes containing a large number of bristles. Temperature shifts for 5 hours between 34-44 hours APF results in interommatidial bristle loss and an increase in the number of primary pigment cells.
The Dl6B/DlCS20 transheterozygotes show severe defects in wings and legs but relatively robust fertility and have high pupal and adult viability. Ovaries are only mildly affected, even at 29oC.
Mutant exhibit mild hyperplasia of replicating sensory precursors at 18oC: due to an increased number of ectodermal cells being recruited as sensory precursor cells. Hyperplasia increase two- to three-fold at 30oC.
Microchaetae multiplication results from heat pulses 7 to 24 hours after puparium formation, while microchaetae deletion results from heat pulses 24 to 47 hours after puparium formation. Macrochaetae multiplication at high levels results from heat pulses 0 to 5 hours after puparium formation, and later heat pulses can delete macrochaetae.
Embryonic neurogenic phenotype is more severe at 29oC than 18oC. Heterozygotes with Dl9K are lethal at 29oC, imaginal discs display severe defects. The temperature sensitive period is between 25 and 2 hours before puparium formation, reduction in viability at this period is associated with developmental arrest at the pupal molt. Arrested pupae lack pigmentation, have everted eyes, antennal imaginal discs, everted legs that are inflated and wings appear as bloated sacs. Humeral macrochaetaes are deleted at high temperatures but the temperature sensitive period cannot be determined. Heat pulses immediately after pupariation causes multiplication of thoracic microchaetae, the temperature sensitive period for deletion of microchaetae overlaps and extends later in development. Scarring, eye roughening, disruption of the ommatidial array, eye glossiness and multiplication of interommatidial bristles result from heat pulses an hour after puparium formation. Defects in leg development are more severe with increasing heat pulses during the third instar. Wing venariondefects are observed with heat pulses during third instar development but a temperature sensitive period could not be determined.
Dl6B/Dlvi1 embryos show a great reduction in egg laying at the restrictive temperature (32oC). Mislocalization of bcd to the posterior pole of the oocyte and excess of polar cells were evident.
A cluster of bristles is present at the position of the posterior postular bristle (Cagan, Genes and Devel. 3: 1099--1112).
Severity of the phenotype is increased by triploidy for E(spl)+.
Small vein deltas are formed at the wing margin. Rough eye phenotype. Number of bristles in the thoracic segments is frequently increased.
Homozygous clones induced in the eye and thoracic imaginal discs show epidermal development indistinguishable from wild-type at 18oC. Homozygous clones in the eye have a severely disturbed ommatidial pattern, visible as a scar in the eye surface at 29oC. Ommatidia are larger than wild-type and interommatidial bristles are missing. Each ommatidium contains more retinula cells and fewer pigment cells than wild-type. Each ommatidium contains more receptor cells than normal, and may contain up to 13 receptor cells. Homozygous clones in the cuticle have additional bristles at the same positions as normal bristles at 29oC.
Double mutants Dl6B and dl2 gave slight neuralization of the cephalic epidermis. Dl6B derived from dl2/dl2 mothers raised at 18oC show neural hypertrophy in cephalic regions only, at 25oC patchy neuralization in the thoracic and abdominal regions and at 29oC neuralization was found to affect all cells ventral to the tracheal placodes.
Weak embryonic neurogenic phenotype at 18oC: head defects and holes in the ventral epidermis at thoracic and abdominal levels. Intermediate embryonic neurogenic phenotype at 25oC: surviving epidermis consists of dorsal epidermal plate connected to foregut epidermis by thin bridges probably originating from the maxillary segment. Temperature effect is a purely zygotic effect. Phenocritical period is between pole cell formation and ectodermal segmentation.
Like Dl1 except that severity of phenotype in homozygous embryos temperature-sensitive. At 18oC there is patchy neuralization of cephalic and ventral ectoderm; expression more severe at 25oC and extreme at 29oC. Temperature-sensitive period between pole-cell formation and mesodermal segmentation. Clone of ommatidia homozygous for Dl6B, normal when reared under permissive conditions; in flies raised at 29oC, however, ommatidial pattern severely disturbed, producing scarring of the eye surface; ommatidia appear larger than normal and interommatidial bristles missing; homozygous mutant facets contain more than a normal complement of retinula cells-up to 13; cytodifferentiation apparently normal. Cuticular clones exhibit elaboration of extra bristles at bristle-forming sites (Dietrich and Campos-Ortega, 1984). temperature-sensitive