LHX2 Is Necessary for the Maintenance of Optic Identity and for the Progression of Optic Morphogenesis

Abstract

Eye formation is regulated by a complex network of eye field transcription factors (EFTFs) including LIM-homeodomain gene Lhx2. We disrupted Lhx2 function at different stages during this process using a conditional knockout strategy in mice. We find that Lhx2 function is required in an ongoing fashion to maintain optic identity across multiple stages, from the formation of the optic vesicle to the differentiation of the neuroretina. At each stage loss of Lhx2 led to upregulation of a set of molecular markers that are normally expressed in the thalamic eminence and in the anterodorsal hypothalamus in a portion of the optic vesicle or retina. Furthermore, the longer Lhx2 function was maintained, the further optic morphogenesis progressed. Early loss of function caused profound mispatterning of the entire telencephalic-optic-hypothalamic field, such that the optic vesicle became mispositioned and appeared to arise from the diencephalic-telencephalic boundary (DTB). At subsequent stages, loss of Lhx2 did not affect optic vesicle position, but caused arrest of optic cup formation. If Lhx2 was selectively disrupted in the neuroretina from E11.5, the neuroretina showed gross dysmorphology along with aberrant expression of markers specific to the thalamic eminence and anterodorsal hypothalamus. Our findings indicate a continual requirement for Lhx2 throughout the early stages of optic development, not only to maintain optic identity by suppressing alternative fates, but also to mediate multiple steps of optic morphogenesis. These findings provide new insight into the anophthalmic phenotype of the Lhx2 mutant and reveal novel roles for this transcription factor in eye development.

The stage-dependent roles of Ldb1 and functional redundancy with Ldb2 in mammalian retinogenesis

“…Lhx2 is the LIM-HD protein co-expressed with Ldb1 in RPCs in early and late stages of retinogenesis, and is required for maintaining the RPCs (Gordon et al, 2013;Roy et al, 2013;Balasubramanian et al, 2014). To examine the physical interaction between Ldb1 and Lhx2, we conducted coimmunoprecipitation with Ldb1 antibodies, with IgG used as control, from wild-type E15.5 eyes and P0 retinas (Fig.…”

“…Lhx2 is a LIM-HD family member that is expressed in proliferating RPCs (Balasubramanian et al, 2014), and is required for the morphogenesis and patterning of the OV and OC, as well as for maintaining the pool of RPCs (Porter et al, 1997;Yun et al, 2009;Hagglund et al, 2011;Gordon et al, 2013;Roy et al, 2013). Lhx2 expression is also maintained in mature Müller glia, where it controls stress responses (de Melo et al, 2012).…”

Control of lens development by Lhx2-regulated neuroretinal FGFs

“…We recently observed that selective deletion of Lhx2 in neuroretina after lens placode induction led to severe microphthalmia and a near-total loss of the expression of many retinal progenitor-specific genes (Roy et al, 2013). Interestingly, we also noticed severe disruptions of lens development in these animals.…”

“…To identify candidate retinal-derived factors whose expression was altered in Lhx2-deficient neuroretina, we analyzed previously reported microarray data obtained from retinas of control and Chx10-Cre;Lhx2 lox/lox mice at E13.5 (Roy et al, 2013; Accession number GSE87707). These data indicated that multiple different FGFs and FGF-regulated genes showed altered expression in Chx10-Cre;Lhx2 lox/lox retina.…”

“…Haematoxylin and Eosin staining and fluorescence immunohistochemistry were performed as previously described (de Melo et al, 2012;Roy et al, 2013). The following primary antibodies were used: rabbit anti-Lhx2 [1:1000; generated for our lab by Covance (de Melo et …”