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Bridging the synaptic gap: neuroligins and neurexin I in Apis mellifera.

Biswas S, Russell RJ, Jackson CJ, Vidovic M, Ganeshina O, Oakeshott JG, Claudianos C - PLoS ONE (2008)

Bottom Line: Neurexin I and neuroligin expression was found in brain tissue, with expression present throughout development, and in most cases significantly up-regulated in adults.We show neuroligins and neurexins comprise a highly conserved molecular system with likely similar functional roles in insects as vertebrates, and with scope in the honeybee to generate substantial functional diversity through alternative splicing.Our study provides important prerequisite data for using the bee as a model for vertebrate synaptic development.

View Article: PubMed Central - PubMed

Affiliation: University of Queensland, Queensland Brain Institute, Brisbane, Queensland, Australia.

ABSTRACT
Vertebrate studies show neuroligins and neurexins are binding partners in a trans-synaptic cell adhesion complex, implicated in human autism and mental retardation disorders. Here we report a genetic analysis of homologous proteins in the honey bee. As in humans, the honeybee has five large (31-246 kb, up to 12 exons each) neuroligin genes, three of which are tightly clustered. RNA analysis of the neuroligin-3 gene reveals five alternatively spliced transcripts, generated through alternative use of exons encoding the cholinesterase-like domain. Whereas vertebrates have three neurexins the bee has just one gene named neurexin I (400 kb, 28 exons). However alternative isoforms of bee neurexin I are generated by differential use of 12 splice sites, mostly located in regions encoding LNS subdomains. Some of the splice variants of bee neurexin I resemble the vertebrate alpha- and beta-neurexins, albeit in vertebrates these forms are generated by alternative promoters. Novel splicing variations in the 3' region generate transcripts encoding alternative trans-membrane and PDZ domains. Another 3' splicing variation predicts soluble neurexin I isoforms. Neurexin I and neuroligin expression was found in brain tissue, with expression present throughout development, and in most cases significantly up-regulated in adults. Transcripts of neurexin I and one neuroligin tested were abundant in mushroom bodies, a higher order processing centre in the bee brain. We show neuroligins and neurexins comprise a highly conserved molecular system with likely similar functional roles in insects as vertebrates, and with scope in the honeybee to generate substantial functional diversity through alternative splicing. Our study provides important prerequisite data for using the bee as a model for vertebrate synaptic development.

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Structural Homology Modelling.(2.1) shows neuroligin and neurexin I homology models. The similarity between MmNLG1 and (a) AmNLG1 and (b) AmNLG3 is illustrated using colour, where sequence similarity in blue represents identical; green represents conservative; yellow represents semi-conservative and red represents dissimilar. Similarity to Mm β-Nrx1B with AmNrxI_A is illustrated using the same coloured coding. (2.2) shows the putative honeybee neuroligin dimer interfaces. The neuroligin dimer interface from (a) the crystal structure of mouse neuroligin is shown alongside the putative interfaces in (b) AmNLG1 and (c) AmNLG3. In both honeybee sequences the key residues of the ‘hydrophobic core’ are replaced by charged or polar residues. (2.3) illustrates the homology modelling of AmNLG3 aternative slice vriants. The four spliced variants (b–e) of AmNLG3 are shown. Full length AmNLG3 was modelled against mouse NLG1 [73]. Regions missing from the alternative transcripts are highlighted in red. (2.4) shows conservation of the neuroligin-neurexin interface in the honeybee. The respective surfaces of the neuroligin-neurexin interface are shown, based on the crystal structure of the complex from mouse. Sequence similarity is shown (blue, identical; green, conservative; yellow, semi-conservative; red, dissimilar) illustrating, (a) the strong conservation in AmNrxI-A, (b) the moderate conservation in AmNLG1, and (c) the lack of conservation in AmNLG3. (d) Illustrates a potential interaction between AmNrx1-A and AmNLG1, showing the conserved salt bridges (R232-D387), hydrogen bonds (N103-D402), and the potentially complementary hydrophobic and hydrophilic regions at the centre of the interface. Amino acids are coloured by type (blue, basic; red, acidic; yellow, polar; grey, non-polar).
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pone-0003542-g002: Structural Homology Modelling.(2.1) shows neuroligin and neurexin I homology models. The similarity between MmNLG1 and (a) AmNLG1 and (b) AmNLG3 is illustrated using colour, where sequence similarity in blue represents identical; green represents conservative; yellow represents semi-conservative and red represents dissimilar. Similarity to Mm β-Nrx1B with AmNrxI_A is illustrated using the same coloured coding. (2.2) shows the putative honeybee neuroligin dimer interfaces. The neuroligin dimer interface from (a) the crystal structure of mouse neuroligin is shown alongside the putative interfaces in (b) AmNLG1 and (c) AmNLG3. In both honeybee sequences the key residues of the ‘hydrophobic core’ are replaced by charged or polar residues. (2.3) illustrates the homology modelling of AmNLG3 aternative slice vriants. The four spliced variants (b–e) of AmNLG3 are shown. Full length AmNLG3 was modelled against mouse NLG1 [73]. Regions missing from the alternative transcripts are highlighted in red. (2.4) shows conservation of the neuroligin-neurexin interface in the honeybee. The respective surfaces of the neuroligin-neurexin interface are shown, based on the crystal structure of the complex from mouse. Sequence similarity is shown (blue, identical; green, conservative; yellow, semi-conservative; red, dissimilar) illustrating, (a) the strong conservation in AmNrxI-A, (b) the moderate conservation in AmNLG1, and (c) the lack of conservation in AmNLG3. (d) Illustrates a potential interaction between AmNrx1-A and AmNLG1, showing the conserved salt bridges (R232-D387), hydrogen bonds (N103-D402), and the potentially complementary hydrophobic and hydrophilic regions at the centre of the interface. Amino acids are coloured by type (blue, basic; red, acidic; yellow, polar; grey, non-polar).

Mentions: As shown in Figures 2.1a and b, sequence conservation is very strong in the interior of the protein, with the majority of the sequence variation occurring on its surface. In fact, there is 52% sequence identity between solvent-buried regions of the proteins compared to only 19% sequence identity in solvent-exposed regions. This result is consistent with the action of selective pressure to maintain the structural integrity of the α/β hydrolase fold, whereas there is apparently little selective pressure to retain similar sequences at the protein surface [56]. We are particularly interested in sequence conservation in functionally important areas of the neuroligin protein surface, such as the dimerization interface and the neuroligin/neurexin interface (discussed below). The recent elucidation of these interfaces in the mammalian proteins, initially revealed by low resolution X-ray scattering experiments [21] and followed by high resolution crystal structures [50]–[52], allowed us to identify the corresponding regions in our homology model.


Bridging the synaptic gap: neuroligins and neurexin I in Apis mellifera.

Biswas S, Russell RJ, Jackson CJ, Vidovic M, Ganeshina O, Oakeshott JG, Claudianos C - PLoS ONE (2008)

Structural Homology Modelling.(2.1) shows neuroligin and neurexin I homology models. The similarity between MmNLG1 and (a) AmNLG1 and (b) AmNLG3 is illustrated using colour, where sequence similarity in blue represents identical; green represents conservative; yellow represents semi-conservative and red represents dissimilar. Similarity to Mm β-Nrx1B with AmNrxI_A is illustrated using the same coloured coding. (2.2) shows the putative honeybee neuroligin dimer interfaces. The neuroligin dimer interface from (a) the crystal structure of mouse neuroligin is shown alongside the putative interfaces in (b) AmNLG1 and (c) AmNLG3. In both honeybee sequences the key residues of the ‘hydrophobic core’ are replaced by charged or polar residues. (2.3) illustrates the homology modelling of AmNLG3 aternative slice vriants. The four spliced variants (b–e) of AmNLG3 are shown. Full length AmNLG3 was modelled against mouse NLG1 [73]. Regions missing from the alternative transcripts are highlighted in red. (2.4) shows conservation of the neuroligin-neurexin interface in the honeybee. The respective surfaces of the neuroligin-neurexin interface are shown, based on the crystal structure of the complex from mouse. Sequence similarity is shown (blue, identical; green, conservative; yellow, semi-conservative; red, dissimilar) illustrating, (a) the strong conservation in AmNrxI-A, (b) the moderate conservation in AmNLG1, and (c) the lack of conservation in AmNLG3. (d) Illustrates a potential interaction between AmNrx1-A and AmNLG1, showing the conserved salt bridges (R232-D387), hydrogen bonds (N103-D402), and the potentially complementary hydrophobic and hydrophilic regions at the centre of the interface. Amino acids are coloured by type (blue, basic; red, acidic; yellow, polar; grey, non-polar).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2570956&req=5

pone-0003542-g002: Structural Homology Modelling.(2.1) shows neuroligin and neurexin I homology models. The similarity between MmNLG1 and (a) AmNLG1 and (b) AmNLG3 is illustrated using colour, where sequence similarity in blue represents identical; green represents conservative; yellow represents semi-conservative and red represents dissimilar. Similarity to Mm β-Nrx1B with AmNrxI_A is illustrated using the same coloured coding. (2.2) shows the putative honeybee neuroligin dimer interfaces. The neuroligin dimer interface from (a) the crystal structure of mouse neuroligin is shown alongside the putative interfaces in (b) AmNLG1 and (c) AmNLG3. In both honeybee sequences the key residues of the ‘hydrophobic core’ are replaced by charged or polar residues. (2.3) illustrates the homology modelling of AmNLG3 aternative slice vriants. The four spliced variants (b–e) of AmNLG3 are shown. Full length AmNLG3 was modelled against mouse NLG1 [73]. Regions missing from the alternative transcripts are highlighted in red. (2.4) shows conservation of the neuroligin-neurexin interface in the honeybee. The respective surfaces of the neuroligin-neurexin interface are shown, based on the crystal structure of the complex from mouse. Sequence similarity is shown (blue, identical; green, conservative; yellow, semi-conservative; red, dissimilar) illustrating, (a) the strong conservation in AmNrxI-A, (b) the moderate conservation in AmNLG1, and (c) the lack of conservation in AmNLG3. (d) Illustrates a potential interaction between AmNrx1-A and AmNLG1, showing the conserved salt bridges (R232-D387), hydrogen bonds (N103-D402), and the potentially complementary hydrophobic and hydrophilic regions at the centre of the interface. Amino acids are coloured by type (blue, basic; red, acidic; yellow, polar; grey, non-polar).
Mentions: As shown in Figures 2.1a and b, sequence conservation is very strong in the interior of the protein, with the majority of the sequence variation occurring on its surface. In fact, there is 52% sequence identity between solvent-buried regions of the proteins compared to only 19% sequence identity in solvent-exposed regions. This result is consistent with the action of selective pressure to maintain the structural integrity of the α/β hydrolase fold, whereas there is apparently little selective pressure to retain similar sequences at the protein surface [56]. We are particularly interested in sequence conservation in functionally important areas of the neuroligin protein surface, such as the dimerization interface and the neuroligin/neurexin interface (discussed below). The recent elucidation of these interfaces in the mammalian proteins, initially revealed by low resolution X-ray scattering experiments [21] and followed by high resolution crystal structures [50]–[52], allowed us to identify the corresponding regions in our homology model.

Bottom Line: Neurexin I and neuroligin expression was found in brain tissue, with expression present throughout development, and in most cases significantly up-regulated in adults.We show neuroligins and neurexins comprise a highly conserved molecular system with likely similar functional roles in insects as vertebrates, and with scope in the honeybee to generate substantial functional diversity through alternative splicing.Our study provides important prerequisite data for using the bee as a model for vertebrate synaptic development.

View Article: PubMed Central - PubMed

Affiliation: University of Queensland, Queensland Brain Institute, Brisbane, Queensland, Australia.

ABSTRACT
Vertebrate studies show neuroligins and neurexins are binding partners in a trans-synaptic cell adhesion complex, implicated in human autism and mental retardation disorders. Here we report a genetic analysis of homologous proteins in the honey bee. As in humans, the honeybee has five large (31-246 kb, up to 12 exons each) neuroligin genes, three of which are tightly clustered. RNA analysis of the neuroligin-3 gene reveals five alternatively spliced transcripts, generated through alternative use of exons encoding the cholinesterase-like domain. Whereas vertebrates have three neurexins the bee has just one gene named neurexin I (400 kb, 28 exons). However alternative isoforms of bee neurexin I are generated by differential use of 12 splice sites, mostly located in regions encoding LNS subdomains. Some of the splice variants of bee neurexin I resemble the vertebrate alpha- and beta-neurexins, albeit in vertebrates these forms are generated by alternative promoters. Novel splicing variations in the 3' region generate transcripts encoding alternative trans-membrane and PDZ domains. Another 3' splicing variation predicts soluble neurexin I isoforms. Neurexin I and neuroligin expression was found in brain tissue, with expression present throughout development, and in most cases significantly up-regulated in adults. Transcripts of neurexin I and one neuroligin tested were abundant in mushroom bodies, a higher order processing centre in the bee brain. We show neuroligins and neurexins comprise a highly conserved molecular system with likely similar functional roles in insects as vertebrates, and with scope in the honeybee to generate substantial functional diversity through alternative splicing. Our study provides important prerequisite data for using the bee as a model for vertebrate synaptic development.

Show MeSH
Related in: MedlinePlus