Expression of Lhx6 in the adult and developing mouse retina

Abstract

Purpose

To investigate the expression patterns of LIM Homeobox 6 (Lhx6) in the adult and developing mouse retina.

Methods

The Lhx6-GFP knock-in allele was used to activate constitutive expression of a GFP reporter in Lhx6 expressing cells. Double labeling with GFP and retinal markers in the mouse retina at postnatal day 56 (P56) was performed to identify the cell types expressing Lhx6. To determine the neuronal cell types that express Lhx6, double labeling with GFP and various retinal markers was employed in the differentiating retina at P7 and P15.

Results

GFP + Lhx6 lineage cells were determined in Brn3a + retinal ganglion cells (RGCs), ChAT + amacrine cells (ACs), and Islet-class LIM-homeodomain 1 (Isl1+) ACs in the mouse retina at P56. In the ganglion cell layer (GCL), Lhx6 was expressed in Brn3a + RGCs but not Brn3b + RGCs at P15. Moreover, in the inner nuclear layer (INL), Lhx6 was not expressed in Bhlhb5+ ACs at P15. However, Lhx6 was weakly expressed in Glyt1+ ACs and Pax6+ ACs, and strongly expressed in Isl1+ and ChAT + ACs at P15.

Conclusion

Lhx6 was expressed in RGCs and ACs in both the adult and developing mouse retina.

Introduction

The LIM homeodomain family of transcription factors plays a role in many processes involved in interneuron migration and development (Bourgouin et al., 1992; Ericson et al., 1992; Taira et al., 1995; Hobert and Westphal, 2000). Lhx6, a member of this family, is expressed in the medial ganglionic eminence (MGE) of the ventral telencephalon where the vast majority of cortical interneurons are generated (Grigoriou et al., 1998; Kimura et al., 1999; Lavdas et al., 1999). Lhx6 is required for tangential migration of GABAergic interneuron progenitors, and for their correct distribution in the cortical layers of postnatal animals (Alifragis et al., 2004).

The expression of Lhx6 begins embryonically in retinal progenitors at the embryonic stage (E13.5), and is expressed in cells in the ganglion cells layer (GCL), as well as in the outer portion of the inner nuclear layer (INL) (Balasubramanian et al., 2014). To confirm the expression of Lhx6 during retinal development in mice, the Lhx6-GFP knock-in allele was used to activate constitutive expression of a GFP reporter in Lhx6 expressing cells. By performing double labeling experiments using GFP and retinal markers in the mouse retina at P56, we found that GFP + Lhx6 lineage cells were predominantly expressed in amacrine cells (ACs) and retinal ganglion cells (RGCs) in the adult retina. Retinal sections at P5, P6, P8, P15, P21, and P28 were stained with GFP to validate the initial time of expression and location of Lhx6 in the developing mouse retina. To determine the neuronal cell types that express Lhx6, double labeling experiments were performed using GFP and various retinal cell markers in the differentiating retina at P7 and P15. Our findings showed that Lhx6 may contribute to cell-fate determination or maturation of retinal cells not only in RGCs but also in subsets of ACs.