Flat contacts of OFF bipolar cell dendrites with cones.

<p><b>A-F:</b> Electron microscopic images of OFF bipolar cell dendrites labeled via pre-embedding immunohistochemistry in vertical sections from <i>Nrl</i>^-/- (A-D) and wild-type retinas (E,F). Types 1 and 2 bipolar cells were labeled with NK3R (A,B,E), type 4 bipolar cells with calsenilin (Csen, C,D,F). Presynaptic ribbons in cone(-like) photoreceptor terminals are indicated by arrowheads. Putative postsynaptic OFF bipolar cell contacts are marked by arrows where cone membranes appeared thickened and darker than those in surrounding areas, typically indicative of presynaptic contact sites. Scale bar = 1 μm for all panels.</p

Dendritic stratification patterns of OFF bipolar cells.

<p><b>A-P:</b> Maximum intensity projections of confocal image stacks from vertical cryosections of wild-type (A-H) and <i>Nrl</i>^-/- (I-P) mice double-labeled with ribbon markers bassoon (A) or CtBP2 (all other). OFF bipolar cells were labeled with antibodies against NK3R (types 1 and 2; A,B,I,J), HCN4 (type 3a; C,D,K,L), PKARIIβ (type 3b; E,F,M,N), and calsenilin (Csen, type 4; G,H,O,P). Dashed lines in O indicate the inner and outer border of the CtBP2 labeled area (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0173455#pone.0173455.g002" target="_blank">Fig 2A</a> for more details). Scale bar = 10 μm for all panels.</p

Table_1_Genetic Control of Rod Bipolar Cell Number in the Mouse Retina.PDF

<p>Genetic variants modulate the numbers of various retinal cell types in mice. For instance, there is minimal variation in the number of rod bipolar cells (RBCs) in two inbred strains of mice (A/J and C57BL/6J), yet their F1 offspring contain significantly more RBCs than either parental strain. To investigate the genetic source of this variation, we mapped the variation in the number of RBCs across 24 genetically distinct recombinant inbred (RI) strains (the AXB/BXA strain-set), seeking to identify quantitative trait loci (QTL). We then sought to identify candidate genes and potential casual variants at those genomic loci. Variation in RBC number mapped to three genomic loci, each modulating cell number in excess of one-third of the range observed across the RI strains. At each of these loci, we identified candidate genes containing variants that might alter gene function or expression. The latter genes were also analyzed using a transcriptome database, revealing a subset for which expression correlated with variation in RBC number. Using an electroporation strategy, we demonstrate that early postnatal expression of one of them, Ggct (gamma-glutamyl cyclotransferase), modulates bipolar cell number. We identify candidate regulatory variants for this gene, finding a large structural variant (SV) in the putative promoter that reduces expression using a luciferase assay. This SV reducing Ggct expression in vitro is likely the causal variant within the gene associated with the variation in Ggct expression in vivo, implicating it as a quantitative trait variant (QTV) participating in the control of RBC number.</p

Image_1_Genetic Control of Rod Bipolar Cell Number in the Mouse Retina.PDF

<p>Genetic variants modulate the numbers of various retinal cell types in mice. For instance, there is minimal variation in the number of rod bipolar cells (RBCs) in two inbred strains of mice (A/J and C57BL/6J), yet their F1 offspring contain significantly more RBCs than either parental strain. To investigate the genetic source of this variation, we mapped the variation in the number of RBCs across 24 genetically distinct recombinant inbred (RI) strains (the AXB/BXA strain-set), seeking to identify quantitative trait loci (QTL). We then sought to identify candidate genes and potential casual variants at those genomic loci. Variation in RBC number mapped to three genomic loci, each modulating cell number in excess of one-third of the range observed across the RI strains. At each of these loci, we identified candidate genes containing variants that might alter gene function or expression. The latter genes were also analyzed using a transcriptome database, revealing a subset for which expression correlated with variation in RBC number. Using an electroporation strategy, we demonstrate that early postnatal expression of one of them, Ggct (gamma-glutamyl cyclotransferase), modulates bipolar cell number. We identify candidate regulatory variants for this gene, finding a large structural variant (SV) in the putative promoter that reduces expression using a luciferase assay. This SV reducing Ggct expression in vitro is likely the causal variant within the gene associated with the variation in Ggct expression in vivo, implicating it as a quantitative trait variant (QTV) participating in the control of RBC number.</p