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Gap junction proteins are not interchangeable in development of neural function in the Drosophila visual system

Molecular, Cellular and Developmental Biology, Yale University, New Haven, CT 06511, USA

View larger version (7K): [in a new window]   Fig. 1. Electroretinograms of shakB2 and ogrecb8 animals. ERGs of both mutants are defective in on- and off-transients, suggesting a reduction in or loss of functional chemical synaptic connections between the retina and lamina in these mutants. (A) ERG of wild-type (Canton-S) flies, vertical arrows mark the on- and off-transients, respectively. (B) ERG of shakB2 animals. (C) ERG of ogrecb8 animals.

View larger version (18K): [in a new window]   Fig. 2. Rescue of ogrecb8 and shakB2 ERGs. (A,C) Negative controls. (A) ogrecb8 with ogre promoter-Gal4 driver only and (C) shakB2 with elav-Gal4 driver only. (B) ERG of ogrecb8 animals rescued by expression of the ogre protein via an ogre promoter-Gal4 driver. (D) ERG of shakB2 animals rescued by expression of shakB(N) in all neurons via the elav-Gal4 driver. Compare these ERGs with wild-type in Fig. 1A. ShakB(N)-ogre chimeric proteins that contain the first half of ogre rescue ogrecb8 but not shakB2, whereas those that contain the first half of shakB(N) rescue shakB2 but not ogrecb8. (E) ogrecb8 is rescued by ogre1-182shakB(N)172-end. (F) ogrecb8 is not rescued by shakB(N)1-172ogre183-end. (G) shakB2 is not rescued by ogre1-182shakB(N)173-end. (H) shakB2 is rescued by shakB(N)1-172ogre183-end.

View larger version (81K): [in a new window]   Fig. 3. A pile-up of the Drosophila innexin family showing conserved residues in black. Putative transmembrane domains are underlined and marked as M1, M2 etc. Horizontal lines mark the breakpoints for the chimeras we tested and are labeled with the shakB(N) residue number on the left and the corresponding ogre residue number on the right. D-inx-7 rescues shakB2 whereas ogre does not. In addition, the chimeric studies show that residues 97-172 of shakB(N) are the residues needed for shakB(N) specificity. In this critical region those residues where D-inx-7 is identical or chemically similar to shakB(N), but chemically different from ogre, are marked with asterisks. These marked residues are likely to be the ones that are most crucial for shakB(N)-specific rescue.

View larger version (15K): [in a new window]   Fig. 4. A comparison of the amino-acid sequence of shakB(N) and shakB(L) coded by the divergent first coding exons. The sequences that differ between the two are all within the first approximately one third of the protein, from the start through the first extracellular loop. From this point on the two proteins are identical.

View larger version (28K): [in a new window]   Fig. 5. A schematic of the shakB(N)-ogre chimeric proteins used to rescue shakB2 and ogrecb8 animals. shakB(N) sequences are represented in black and ogre sequences in grey. Beneath each schematic, the ability of each chimera to rescue the on- and off-transients of shakB2 and ogrecb8 mutants as compared with the wild-type protein is shown. The rescue ability is calculated as in the following example:. Small negative values and small positive values less than 5% were labelled as 0% rescue.