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A glial variant of the vesicular monoamine transporter is required to store histamine in the Drosophila visual system.

Romero-Calderón R, Uhlenbrock G, Borycz J, Simon AF, Grygoruk A, Yee SK, Shyer A, Ackerson LC, Maidment NT, Meinertzhagen IA, Hovemann BT, Krantz DE - PLoS Genet. (2008)

Bottom Line: In mammals, vesicular monoamine transporters (VMATs) are expressed exclusively in neurons and mediate the storage of histamine and other monoamines.We report here that a novel mRNA splice variant of Drosophila VMAT (DVMAT-B) is expressed not in neurons but rather in a small subset of glia in the lamina of the fly's optic lobe.Our results suggest a novel role for a monoamine transporter in glia that may be relevant to histamine homeostasis in other systems.

View Article: PubMed Central - PubMed

Affiliation: Gonda Goldschmied Center for Neuroscience and Genetics Research, David Geffen School of Medicine at University of California Los Angeles, Los Angeles, California, United States of America.

ABSTRACT
Unlike other monoamine neurotransmitters, the mechanism by which the brain's histamine content is regulated remains unclear. In mammals, vesicular monoamine transporters (VMATs) are expressed exclusively in neurons and mediate the storage of histamine and other monoamines. We have studied the visual system of Drosophila melanogaster in which histamine is the primary neurotransmitter released from photoreceptor cells. We report here that a novel mRNA splice variant of Drosophila VMAT (DVMAT-B) is expressed not in neurons but rather in a small subset of glia in the lamina of the fly's optic lobe. Histamine contents are reduced by mutation of dVMAT, but can be partially restored by specifically expressing DVMAT-B in glia. Our results suggest a novel role for a monoamine transporter in glia that may be relevant to histamine homeostasis in other systems.

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Mutant alleles of dVMAT reduce expression of DVMAT-A and -B.(A) dVMAT-A and -B share a common translational start site (indicated as “A, B start”) and a common N-terminus, but diverge at their C-termini. Coding exons in the dVMAT gene that are common to both dVMAT-A and-B are shown as gray boxes, introns as black lines. To generate alternative carboxy termini, the indicated genomic sequence (magenta box) is spliced out from dVMAT-A and retained in dVMAT-B. The in situ probe for dVMAT-B contains the first 260 nucleotides of this sequence. The P element insert in the dVMAT mutant allele dVMATP1 (black arrowhead) disrupts the coding sequence of both dVMAT-A and -B. (B,C) In situ hybridization of head sections shows transcription of the dVMAT-B gene in a layer between the retina and lamina (B). Magnified view of (B) shown in (C). (D) Cartoons showing the predicted topology of DVMAT with lumenal domains above and cytoplasmic domains below the parallel gray lines representing the vesicle membrane. Open circles indicate domains shared by DVMAT-A and -B. Filled, magenta circles indicate the C-terminal domain specific for DVMAT-B. The P element insertion site in the last exon of the dVMATP1 (marked with “P” and a black arrowhead) functionally deletes transmembrane domains 11 and 12 and the C-terminus (shaded gray). The imprecise excision allele dVMATΔ14 results in an insertion of 51 base pairs, and 17 amino acids in-frame with the original downstream codons (marked as “Δ14” with a blue arrowhead, with blue circles indicating the inserted residues). (E) Western blot using the N-terminus antibody directed against both DVMAT-A and -B splice variants shows an absence of DVMAT protein in dVMATP1 homozygotes (P/P), and dramatically reduced levels in dVMATΔ14 (Δ14/Δ14), compared with heterozygous controls (P/CyO and Δ14/CyO). The plasma membrane associated protein Late Bloomer (indicated as “lb”) was used as a loading control. Re, retina; La, lamina; Me, medulla. Bars: (B) 50 microns, (C) 20 microns.
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pgen-1000245-g001: Mutant alleles of dVMAT reduce expression of DVMAT-A and -B.(A) dVMAT-A and -B share a common translational start site (indicated as “A, B start”) and a common N-terminus, but diverge at their C-termini. Coding exons in the dVMAT gene that are common to both dVMAT-A and-B are shown as gray boxes, introns as black lines. To generate alternative carboxy termini, the indicated genomic sequence (magenta box) is spliced out from dVMAT-A and retained in dVMAT-B. The in situ probe for dVMAT-B contains the first 260 nucleotides of this sequence. The P element insert in the dVMAT mutant allele dVMATP1 (black arrowhead) disrupts the coding sequence of both dVMAT-A and -B. (B,C) In situ hybridization of head sections shows transcription of the dVMAT-B gene in a layer between the retina and lamina (B). Magnified view of (B) shown in (C). (D) Cartoons showing the predicted topology of DVMAT with lumenal domains above and cytoplasmic domains below the parallel gray lines representing the vesicle membrane. Open circles indicate domains shared by DVMAT-A and -B. Filled, magenta circles indicate the C-terminal domain specific for DVMAT-B. The P element insertion site in the last exon of the dVMATP1 (marked with “P” and a black arrowhead) functionally deletes transmembrane domains 11 and 12 and the C-terminus (shaded gray). The imprecise excision allele dVMATΔ14 results in an insertion of 51 base pairs, and 17 amino acids in-frame with the original downstream codons (marked as “Δ14” with a blue arrowhead, with blue circles indicating the inserted residues). (E) Western blot using the N-terminus antibody directed against both DVMAT-A and -B splice variants shows an absence of DVMAT protein in dVMATP1 homozygotes (P/P), and dramatically reduced levels in dVMATΔ14 (Δ14/Δ14), compared with heterozygous controls (P/CyO and Δ14/CyO). The plasma membrane associated protein Late Bloomer (indicated as “lb”) was used as a loading control. Re, retina; La, lamina; Me, medulla. Bars: (B) 50 microns, (C) 20 microns.

Mentions: The mRNA of dVMAT is alternatively processed to yield two variants [47]. In dVMAT-B, the segment indicated in Figure 1A is retained. In dVMAT-A, all of the splice sites are used and the indicated segment is removed as an intron. To determine the expression pattern of dVMAT-B mRNA in the adult brain, we performed in situ hybridization experiments. To generate a cDNA probe specific for dVMAT-B, we amplified the sequence retained in dVMAT-B mRNA and removed from dVMAT-A (Figure 1A, “B in situ probe”). Using this probe we observed a narrow band of labeling in the region just beneath the retina (Figure 1B and 1C). These data are consistent with a previous report showing that a probe common to both dVMAT-A+B labels a thin band below the retina in addition to aminergic neurons in the central brain and optic ganglia [56]. Based on this labeling pattern and proximity to the glial marker Neurexin IV, it was suggested that dVMAT might be expressed in the fenestrated glia [56].


A glial variant of the vesicular monoamine transporter is required to store histamine in the Drosophila visual system.

Romero-Calderón R, Uhlenbrock G, Borycz J, Simon AF, Grygoruk A, Yee SK, Shyer A, Ackerson LC, Maidment NT, Meinertzhagen IA, Hovemann BT, Krantz DE - PLoS Genet. (2008)

Mutant alleles of dVMAT reduce expression of DVMAT-A and -B.(A) dVMAT-A and -B share a common translational start site (indicated as “A, B start”) and a common N-terminus, but diverge at their C-termini. Coding exons in the dVMAT gene that are common to both dVMAT-A and-B are shown as gray boxes, introns as black lines. To generate alternative carboxy termini, the indicated genomic sequence (magenta box) is spliced out from dVMAT-A and retained in dVMAT-B. The in situ probe for dVMAT-B contains the first 260 nucleotides of this sequence. The P element insert in the dVMAT mutant allele dVMATP1 (black arrowhead) disrupts the coding sequence of both dVMAT-A and -B. (B,C) In situ hybridization of head sections shows transcription of the dVMAT-B gene in a layer between the retina and lamina (B). Magnified view of (B) shown in (C). (D) Cartoons showing the predicted topology of DVMAT with lumenal domains above and cytoplasmic domains below the parallel gray lines representing the vesicle membrane. Open circles indicate domains shared by DVMAT-A and -B. Filled, magenta circles indicate the C-terminal domain specific for DVMAT-B. The P element insertion site in the last exon of the dVMATP1 (marked with “P” and a black arrowhead) functionally deletes transmembrane domains 11 and 12 and the C-terminus (shaded gray). The imprecise excision allele dVMATΔ14 results in an insertion of 51 base pairs, and 17 amino acids in-frame with the original downstream codons (marked as “Δ14” with a blue arrowhead, with blue circles indicating the inserted residues). (E) Western blot using the N-terminus antibody directed against both DVMAT-A and -B splice variants shows an absence of DVMAT protein in dVMATP1 homozygotes (P/P), and dramatically reduced levels in dVMATΔ14 (Δ14/Δ14), compared with heterozygous controls (P/CyO and Δ14/CyO). The plasma membrane associated protein Late Bloomer (indicated as “lb”) was used as a loading control. Re, retina; La, lamina; Me, medulla. Bars: (B) 50 microns, (C) 20 microns.
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pgen-1000245-g001: Mutant alleles of dVMAT reduce expression of DVMAT-A and -B.(A) dVMAT-A and -B share a common translational start site (indicated as “A, B start”) and a common N-terminus, but diverge at their C-termini. Coding exons in the dVMAT gene that are common to both dVMAT-A and-B are shown as gray boxes, introns as black lines. To generate alternative carboxy termini, the indicated genomic sequence (magenta box) is spliced out from dVMAT-A and retained in dVMAT-B. The in situ probe for dVMAT-B contains the first 260 nucleotides of this sequence. The P element insert in the dVMAT mutant allele dVMATP1 (black arrowhead) disrupts the coding sequence of both dVMAT-A and -B. (B,C) In situ hybridization of head sections shows transcription of the dVMAT-B gene in a layer between the retina and lamina (B). Magnified view of (B) shown in (C). (D) Cartoons showing the predicted topology of DVMAT with lumenal domains above and cytoplasmic domains below the parallel gray lines representing the vesicle membrane. Open circles indicate domains shared by DVMAT-A and -B. Filled, magenta circles indicate the C-terminal domain specific for DVMAT-B. The P element insertion site in the last exon of the dVMATP1 (marked with “P” and a black arrowhead) functionally deletes transmembrane domains 11 and 12 and the C-terminus (shaded gray). The imprecise excision allele dVMATΔ14 results in an insertion of 51 base pairs, and 17 amino acids in-frame with the original downstream codons (marked as “Δ14” with a blue arrowhead, with blue circles indicating the inserted residues). (E) Western blot using the N-terminus antibody directed against both DVMAT-A and -B splice variants shows an absence of DVMAT protein in dVMATP1 homozygotes (P/P), and dramatically reduced levels in dVMATΔ14 (Δ14/Δ14), compared with heterozygous controls (P/CyO and Δ14/CyO). The plasma membrane associated protein Late Bloomer (indicated as “lb”) was used as a loading control. Re, retina; La, lamina; Me, medulla. Bars: (B) 50 microns, (C) 20 microns.
Mentions: The mRNA of dVMAT is alternatively processed to yield two variants [47]. In dVMAT-B, the segment indicated in Figure 1A is retained. In dVMAT-A, all of the splice sites are used and the indicated segment is removed as an intron. To determine the expression pattern of dVMAT-B mRNA in the adult brain, we performed in situ hybridization experiments. To generate a cDNA probe specific for dVMAT-B, we amplified the sequence retained in dVMAT-B mRNA and removed from dVMAT-A (Figure 1A, “B in situ probe”). Using this probe we observed a narrow band of labeling in the region just beneath the retina (Figure 1B and 1C). These data are consistent with a previous report showing that a probe common to both dVMAT-A+B labels a thin band below the retina in addition to aminergic neurons in the central brain and optic ganglia [56]. Based on this labeling pattern and proximity to the glial marker Neurexin IV, it was suggested that dVMAT might be expressed in the fenestrated glia [56].

Bottom Line: In mammals, vesicular monoamine transporters (VMATs) are expressed exclusively in neurons and mediate the storage of histamine and other monoamines.We report here that a novel mRNA splice variant of Drosophila VMAT (DVMAT-B) is expressed not in neurons but rather in a small subset of glia in the lamina of the fly's optic lobe.Our results suggest a novel role for a monoamine transporter in glia that may be relevant to histamine homeostasis in other systems.

View Article: PubMed Central - PubMed

Affiliation: Gonda Goldschmied Center for Neuroscience and Genetics Research, David Geffen School of Medicine at University of California Los Angeles, Los Angeles, California, United States of America.

ABSTRACT
Unlike other monoamine neurotransmitters, the mechanism by which the brain's histamine content is regulated remains unclear. In mammals, vesicular monoamine transporters (VMATs) are expressed exclusively in neurons and mediate the storage of histamine and other monoamines. We have studied the visual system of Drosophila melanogaster in which histamine is the primary neurotransmitter released from photoreceptor cells. We report here that a novel mRNA splice variant of Drosophila VMAT (DVMAT-B) is expressed not in neurons but rather in a small subset of glia in the lamina of the fly's optic lobe. Histamine contents are reduced by mutation of dVMAT, but can be partially restored by specifically expressing DVMAT-B in glia. Our results suggest a novel role for a monoamine transporter in glia that may be relevant to histamine homeostasis in other systems.

Show MeSH
Related in: MedlinePlus