The wings of Fas2e76 mutants raised at 18[o]C are abnormally elongated.
Fas2EB112/Fas2e76 adults display a rough-eye phenotype. Ommatidial photoreceptor and cone cell numbers are disrupted, and in some cases mini-clusters of ommatidia are observed.
When Fas2 is simultaneously decreased in both pre- and post-synaptic cells in Fas2e76 heterozygotes, the result is a small but significant increase in bouton number. This change in bouton number is not attributable to changes in muscle size, which is indistinguishable from wild-type controls. Satellite bouton number in Fas2e76 heterozygotes decreases to 33% the wild-type value. These bouton buds are similar to those observed in wild-type, including the distribution of synaptic vesicles, active zones, and post-synaptic specialisations.
Fas2e76/+ heterozygotes exhibit EJPs with significantly larger amplitudes than wild-type controls.
The motor neuron that innervates DLMa has a higher number of contact points with the muscle in Fas2e76 mutants; there is an average of 5.8 contact points in Fas2e76 mutants vs. 4-6 in wild type. This phenotype also occurs in Fas2e76/Fas2EB112 transheterozygotes: these mutants have an average of 6 contact points per DLMa. The DLMa is 11% longer in Fas2e76/Fas2EB112 mutants than wild type. Investigation of adult innervation pattern in Fas2e76/Fas2EB112 mutants shows that outgrowth of secondary branches is not affected, but that branch elaboration, which occurs at 18-24 hours APF, is affected. During this stage, the average length of Fas2e76/Fas2EB112 secondary branches is increased, as is the area occupied by the higher order arbors of the secondary branches. Additionally, a higher level of secondary branches are stabilized, as shown by staining for futsch, in Fas2e76/Fas2EB112 mutants at 24 hours APF than wild type.
Fas2e76 mutants exhibit normal axon patterns. There are sporadic single BM axon defects, but no OP axon alterations are found.
Fas2e76/Fas2EB112 mutants exhibit normal axon patterns. There are sporadic single BM axon defects, but no OP axon alterations are found.
Synaptic bouton number is significantly reduced at the NMJs of third instar larval Fas2e76 mutants.
The increase in frequency seen in the synaptic drive to aCC/RP2 during the first 28hr of larval life is not affected in the hypomorphic Fas2e76.
Heterozygous Fas2e76/+ flies, in which Fas2 levels are ~50% of wild-type, exhibit a striking increase in bouton number. Homozygous Fas2e76 flies do not exhibit an additional increase in bouton number.
In 14% of the mushroom bodies of mutant animals, an abnormal lobe morphology is seen.
The number of boutons at the neuromuscular junction is reduced by 34% in Fas2e76 larvae compared to wild type.
The morphology of the larval visual system (LVS) is disrupted in most homozygous embryos. Disruption of Bolwig's organ (BO) development can be seen as early as stage 13, when unclustered photoreceptor cells can be seen located near the normal BOs. Later defects include BOs that are smaller than normal, failure of BOs to migrate properly and the presence of nodules along the nerve in some embryos.
The RP3 and 6/7b neurons which innervate longitudinal muscles 6 and 7 have reduced terminals and fewer but larger varicosities in Fas2e76 mutant larvae compared to wild-type.
The morphology of the subsynaptic reticulum at type I boutons appears normal in hemizygous flies. There is an increase in the number of active zones within type I boutons.
Fas2e76/Fas2e93 transheterozygotes exhibit a 50% increase in number of MN boutons at muscle 6. Mild heat induced expression of CrebB-17Aa.hs during larval stages significantly increases the quantal content of the synapse without altering quantal size (as shown by measuring excitatory postsynaptic potential, EPSP). Homozygotes exhibit a 30%-40% reduction in number of boutons, mild heat induced expression of CrebB-17Aa.hs during larval stages does not change the quantal content of the synapse.
In homozygous embryos the SNb fails to diverge from the ISN partially (partial bypass) in 6% segments.
Growth of the synapse reduces when Fas2 expression level is low causing a drop in number of boutons. In Fas2e76/Fas2e93 transheterozygotes growth of the synapse increases as Fas2 expression level is low causing a rise in number of boutons.
Mutant exhibits a reduced number of nerve terminal varicosities at third instar larval neuromuscular junctions. Assaying synaptic transmission demonstrates there is no major alteration in synaptic strength at the whole muscle cell level in these mutants. Ultrastructural characteristics of individual synapses are adjusted to counteract the reduction in the number of nerve terminal varicosities, thereby maintaining the physiological properties of transmission.
Homozygous heads often appear wild type, one or both postvertical bristle can be missing, at 17oC both bristles are missing. Transheterozygotes with Fas2EB112 exhibit missing postvertical, ocellar, vertical and orbital bristles. At 17oC the phenotype is more penetrant with missing ocelli.
Striking defasciculation of the FN3 pathway axons.
Normal grooming behaviour.
Homozygotes show reduced viability. Transheterozygotes for Fas2EB112 and Fas2e76 are sterile. Increased branching of wing sensory axons in discs during metamorphosis. Ectopic sensory neurons are displayed in the wing.
At embryonic stage 12/1 and early stage 13, the MP1, dMP2 and vMP2 growth cones are stalled in Fas2e76 mutants, as is seen in Fas2EB112 and Fas2eB78 mutants. However by late stage 13 and early stage 14, these growth cones often extend towards each other and fasiculate, although in a delayed and variable way, in Fas2e76 mutants. In Fas2e76 mutants, different segments within the same embryo can display different lengths of MP1 extension and differences in axon trajectories. Nevertheless, the MP1 pathway ultimately forms in most segments in Fas2e76 mutants.