Homozygous motor neuron clones examined in the third instar larva show strong defects in neuromuscular junction architecture and bouton morphology (discrete bouton structures are poorly recognisable).
The central nervous system of jebk05644 mutants appears morphologically normal in terms of segmental nerve branching and segmental muscle patterning. Neuropil synaptic differentiation appears normal in these mutants, with comparable labeling intensity, density and distribution of presynaptic and postsynaptic labels.
jebk05644 mutant neuromuscular junctions appear correctly and stereotypically formed and elaborated, with no examples of muscle innervation failure or synaptic targeting errors. mutant presynaptic active zones appear normally formed and with wild-type size.
Homozygous jebk05644 mutants exhibit reduced hatching and mutant larval movement is typically sluggish and highly limited. Locomotory movement in jebk05644 mutants is decreased to 20% of the control level, characterised by slower contractions and extended pauses. Severely impaired and motionless larvae remain capable of briefly resuming movement when stimulated, suggesting a defect in the central circuit output driving locomotion.
jebk05644 mutant neuromuscular junctions exhibit visible glutamate-driven muscle contractions, and consistently large and robust postsynaptic current amplitudes compared to controls. jebk05644 mutant neuromuscular junctions display excitatory junction currents that are comparable to controls, with amplitudes of greater than 1nA.
In jebk05644 mutants, no large (exceeding 500pA) or patterned EJCs are recorded. EJCs are absent in 60% of recordings, and overall EJC frequency is below 1Hz in 40% of active cells.
jebk05644 mutants show a salivary gland phenotype. At stage 14, mutant salivary glands remain associated with the inner circular muscle layer, while in wild type, these structures become separate. After stage 15, cells from the distal tips of the jebk05644 salivary glands spread into the region of the undifferentiated midgut that forms the gastric caecae in the wild-type embryos. The mutant glands become mispositioned and/or elongated and maintain contact with the area of the midgut immediately adjacent to the proventriculus.
jebk05644 homozygous larvae do not ingest food, and lack discernible intestinal structures. In stage 13 jebk05644 homozygous embryos, visceral mesoderm cells are scattered rather than forming an organized band of cells as they would normally do at this stage. At stage 11, the earliest stage at which a mutant phenotype in the visceral mesoderm can clearly be observed, these embryos lack muscle founder cells. However, myoblasts do form in the visceral mesoderm, and go on to contribute to somatic muscle (i.e.- they are fusion competent.)
Differentiated visceral mesoderm is not seen in mutant embryos, although other mesodermal tissues (somatic muscles, heart, fat body and hemocytes) develop normally. Visceral mesoderm precursor cells are specified but fail to migrate normally. There is an increase in the number of nuclei in positions consistent with an increase in somatic muscle precursors, but there is no major disruption of somatic muscle patterning. The midgut endoderm is specified normally and migrates to form two longitudinal bands. Subsequent dorsal and ventral endoderm migration is abnormal (probably because this migration depends on the visceral mesoderm).