Syngr¹ mutant animals are viable, fertile and appear behaviourally normal. They develop at a similar rate and have a normal lifespan compared to control animals. Motor function and coordination appear unaffected at both the larval and adult stages. Syngr¹ mutant males are capable of performing all aspects of the courtship ritual.

At Syngr¹ mutant third instar larval neuromuscular junctions, overall synaptic morphology is normal with no obvious overgrowth, undergrowth or satellite boutons. The total number of synaptic boutons at muscle 6/7 of segment A3 is unchanged compared with controls. There is no significant difference in muscle size and the number of active zones appears normal, with no noticeable alterations in active zone size or spacing.

At the ultrastructural level, boutons at the third instar larval neuromuscular junction in Syngr¹ mutants display changes in synaptic vesicle diameter and density. While the diameter the synaptic vesicles in some Syngr¹ boutons appear similar to controls, there is increase in variability, with 30-40% of boutons having an increased number of large cisternal-like synaptic vesicles. The mean synaptic vesicle size is increased compared to controls. Approximately 10% of Syngr¹ boutons show a marked decrease in synaptic vesicle density; many Syngr¹ boutons appear normal, but overall there is a slight but statistically significant decrease in the density of synaptic vesicles.

Spontaneous miniature Excitatory Junctional Currents (mEJCs) recorded in Syngr¹ mutant third instar larvae reveal a significant increase in quantal size compared to controls. Syngr¹ mutant larvae also display a slight, but significant, decrease in spontaneous mEJC frequency. While mEJC amplitude is increased in Syngr¹, there is no significant change in evoked EJC amplitude, indicating that quantal content is reduced. A significant increase in the paired-pulse ratio is seen, consistent with a reduction in release probability compared to controls. However this increase is transient and not maintained with continued stimulation. Syngr¹ mutant larvae also require a significantly longer time to reach stable pre-tetanus EJC values following post-tetanic depression.

Syngr¹ mutant flies are delayed in resolving endocytic cisternae into synaptic vesicles following a high K[+] shock; at rest the number of cisternae is increased compared to controls, but, as in wild type, the number of cisternae increases in response to incubation in high K[+]. However the number of cisternae remaining 10 minutes after stimulation is higher in Syngr¹ mutants than in controls. Syngr¹ mutant boutons exposed to intense nerve stimulation also show a significantly higher number of endocytic cisternae compared with controls. Unlike at rest, the distribution of synaptic vesicle diameter is similar to controls.

The neuromuscular junctions of Syngr¹ third instar larvae show similar levels of membrane uptake (dye internalisation) to controls in response to nerve stimulation. Levels of dye unloading (following a second, high K[+] stimulation) are also similar to controls. When dye unloading is allowed to occur either in the absence of a second stimulation, or in response to a mild stimulation protocol, the Syngr¹ mutants retain a higher percentage of dye relative to controls.

Syngr¹ is an enhancer of abnormal neurophysiology | adult stage phenotype of Hsap\MAPT^{P301L.QUAS.0N4R}, Ncra\QF^QF2w.nSyb

Syngr¹, shi¹ has abnormal neuroanatomy | third instar larval stage phenotype

Syngr¹ is an enhancer of retina | adult stage phenotype of Hsap\MAPT^{P301L.QUAS.0N4R}, Ncra\QF^QF2w.nSyb