Figure 5.

FIB-SEM Analysis of Mitochondrial Protrusions in Neurons of the Drosophila Protocerebral Bridge

(A) Micrographs showing spatial progression of a mitochondrial protrusion (arrowheads) in the axonal terminal of a protocerebral bridge neuron. Notice the proximity of the protrusion to the clearly visible synaptic vesicles (sv) and T-bar (T)—the characteristics of the Drosophila presynaptic terminal.

(B) Another example of a mitochondrion with a protrusion (arrowheads) in the axonal terminal.

(C) Commonly observed mitochondrial protrusion types—protrusion with a constricted neck (left arrowheads) or with a stubby neck (right arrowheads). In both examples, the protrusions are extensions of mitochondrial outer membranes.

(D and E) Examples illustrating mitochondrial protrusions (arrowheads) in dendrites. The protrusions are positioned immediately at the postsynaptic side of the synapse, as evidenced by the opposing presynaptic T-bar (T) and synaptic vesicles (sv).

(F–H) Examples of dendritic mitochondria whose protrusions (arrowheads) are situated at the base of the neck of a postsynaptic process.

(I) Correlation between number of mitochondrial protrusions and mitochondrial size. Pearson's correlation analysis was used for calculating the r and p values.

The z resolution of the FIB-SEM for the Drosophila protocerebral bridge is 4 nm. The number on the micrograph indicates its z position in the SEM image stack. Scale bars, 100 nm. sv, synaptic vesicles; T, presynaptic T-bar.