Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
, 108 (23), 9697-702

Genetic Modulation of Horizontal Cell Number in the Mouse Retina

Affiliations

Genetic Modulation of Horizontal Cell Number in the Mouse Retina

Irene E Whitney et al. Proc Natl Acad Sci U S A.

Abstract

Neuronal populations display conspicuous variability in their size among individuals, but the genetic sources of this variation are largely undefined. We demonstrate a large and highly heritable variation in neuron number within the mouse retina, affecting a critical population of interneurons, the horizontal cells. Variation in the size of this population maps to the distal end of chromosome (Chr) 13, a region homologous to human Chr 5q11.1-11.2. This region contains two genes known to modulate retinal cell number. Using conditional knock-out mice, we demonstrate that one of these genes, the LIM homeodomain gene Islet-1 (Isl1), plays a role in regulating horizontal cell number. Genetic differences in Isl1 expression are high during the period of horizontal cell production, and cis-regulation of Isl1 expression within the retina is demonstrated directly. We identify a single nucleotide polymorphism in the 5' UTR of Isl1 that creates an E-box sequence as a candidate causal variant contributing to this variation in horizontal cell number.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.
Fig. 1.
Estimated total number (mean and SEM) of horizontal cells in the retina of A/J (white bars) and B6/J (black bars) strain mice, in the B6AF1 progeny (light gray bar), and in 26 RI strains of mice derived from the parental strains (the AXB/BXA strain set; dark gray bars). n = number of mice sampled per strain.
Fig. 2.
Fig. 2.
Genomewide QTL mapping of horizontal cell number. Each chromosome, from centromere to telomere, is represented left to right along the x axis. The Right y axis plots the additive effect, being the extent to which the presence of an A (green line) or B (red line) allele contributes to an increase in horizontal cell number. The Left y axis plots the strength of the linkage of horizontal cell number to different intervals along the genome (blue line). Pink and gray horizontal lines indicate genomewide likelihood ratio statistics (LRS) for significant (<0.05) and suggestive (<0.67) QTL, respectively. A single significant QTL, Hcnc10, at the distal end of chromosome 13 is present.
Fig. 3.
Fig. 3.
(A) Conditional deletion of Fst does not alter horizontal cell density, in either the central or peripheral parts of the retina. (B) Conditional deletion of Isl1 yields an increase in horizontal cell density, relative to littermate control mice, which is most pronounced in the central parts of the retina relative to the periphery. n = number of mice sampled. (C) Retinal fields from the center and periphery of Isl1-CKO mice and control littermates immunolabeled for calbindin. (Scale bar, 100 μm.)
Fig. 4.
Fig. 4.
(A) Cells of the Isl1 lineage born between E12.5 and E16.5, positive for the LacZ reporter gene product β-galactosidase (green), are all positioned in the inner retina on E18.5. (B) Horizontal cell precursors, identified by their expression of Prox1 (magenta), are known to migrate beyond the future horizontal cell stratum in the outer retina, raising the possibility that they too are derived from the Isl1-expressing cells in the inner retina at these early stages. (C) When both channels are viewed together, however, not a single Prox1+ precursor is found to coexpress β-gal. Samples are from the central retina, but identical results were obtained at the far retinal periphery. (Scale bar, 50 μm.)
Fig. 5.
Fig. 5.
(A) Retinal expression of Isl1 during the period of horizontal cell neurogenesis, at E13, shows a nearly fivefold difference favoring A/J (P = 0.0007, Student's t test). A difference is also detected in maturity (P = 0.0028). (B) ASE confirms cis-regulation of Isl1 in AXB/BXA, evidenced by testing the deviation of the allelic expression changes in the retina from the allelic ratio in the genomic DNA in reciprocal F1 hybrids. (P = 0.007). (C) An SNP in the Isl1 5′ UTR creates an E-box sequence in the B6/J strain. The A SNP is the conserved allele. (Alignment generated with CLC Sequence Viewer).

Similar articles

See all similar articles

Cited by 22 articles

See all "Cited by" articles

Publication types

MeSH terms

LinkOut - more resources

Feedback