Dlx1andDlx2function is necessary for terminal differentiation and survival of late-born retinal ganglion cells in the developing mouse retina

Abstract

Dlx homeobox genes, the vertebrate homologs of Distal-less, play important roles in the development of the vertebrate forebrain, craniofacial structures and limbs. Members of the Dlx gene family are also expressed in retinal ganglion cells (RGC), amacrine and horizontal cells of the developing and postnatal retina. Expression begins at embryonic day 12.5 and is maintained until late embryogenesis for Dlx1, while Dlx2expression extends to adulthood. We have assessed the retinal phenotype of the Dlx1/Dlx2 double knockout mouse, which dies at birth. The Dlx1/2 null retina displays a reduced ganglion cell layer (GCL), with loss of differentiated RGCs due to increased apoptosis, and corresponding thinning of the optic nerve. Ectopic expression of Crx, the cone and rod photoreceptor homeobox gene, in the GCL and neuroblastic layers of the mutants may signify altered cell fate of uncommitted RGC progenitors. However,amacrine and horizontal cell differentiation is relatively unaffected in the Dlx1/2 null retina. Herein, we propose a model whereby early-born RGCs are Dlx1 and Dlx2 independent, but Dlx function is necessary for terminal differentiation of late-born RGC progenitors.

GAD isoforms exhibit distinct spatiotemporal expression patterns in the developing mouse lens: Correlation with Dlx2 and Dlx5

“…The absence of Dlx1 and Dlx2 in mice results in neonatal lethality, skeletal abnormalities, and a considerable reduction of forebrain GABAergic inhibitory neurons. This finding is accompanied by a parallel down-regulation of Dlx5, Dlx6, and GAD67 expression (Qiu et al, 1995(Qiu et al, , 1997Anderson et al, 1997a,b;Panganiban and Rubenstein, 2002;de Melo et al, 2003de Melo et al, , 2005Masland, 2005). Because no data are currently available on the possible impact of this mutation on GAD expression in the lens, we sought to determine the expression of different GAD isoforms derived from the GAD67 locus in the Dlx1/Dlx2 mutant lens.…”

“…No obvious lens phenotype has been described for Dlx5/Dlx6 and GAD65/67 knockout mutants, all showing embryonic or neonatal lethality (Asada et al, 1997;Condie et al, 1997;Ji et al, 1999;Panganiban and Rubenstein, 2002;Robledo et al, 2002;de Melo et al, 2005). This finding may be explained by the existence of multiple compensatory mechanisms afforded by genetic (expression of multiple genes of the same family) and functional (cross-regulation from different transcription factors) redundancy of the system during embryonic development, which can result in a later (postnatal) manifestation of the putative GAD/ GABA mutant phenotype.…”

“…DLX2 and GAD immunofluorescence was performed on cryosections from wild-type and Dlx1/Dlx2 knockout mice as described (de Melo et al, 2003(de Melo et al, , 2005. Primary antibodies used were as follows: rabbit anti-DLX2 (1: 400), rabbit anti-GAD25 (rabbit serum #8876, 1:1,000); rabbit anti-GAD44 (rabbit serum #3910, 1:500 raised in the Szabo lab [Szabo et al, 1994]); rabbit serum #6799, 1:500, recognizing GAD25, GAD44, and GAD67 (Katarova et al, 1990); rabbit anti-PROX1 (1:500, courtesy of Dr. M.. Nakafuku).…”

Dlx Homeobox Genes Promote Cortical Interneuron Migration from the Basal Forebrain by Direct Repression of the Semaphorin Receptor Neuropilin-2

“…2A, lanes 2, 6) that was competitively inhibited by unlabeled Nrp-2ii probe (lanes 3, 7). Moreover, the addition of specific anti-DLX1 or anti-DLX2 antibodies to the protein-DNA complex resulted in significant band mobility shifts (lanes 4,8), whereas a nonspecific polyclonal antibody failed to produce such a "supershift" (lanes 5, 9). Neither DLX1 nor DLX2 bind to the first TAAT motif of the Nrp-2ii in vitro.…”

“…There are distinct boundaries of Dlx1 and Dlx2 expression at the pallial-subpallial boundary (1). Insights into the functional role of Dlx genes in development have been primarily gained from analysis of the phenotypes of mice with targeted deletions of Dlx1/Dlx2 (5)(6)(7)(8), Dlx5 (9), and Dlx5/Dlx6 (10). The single Dlx1 and Dlx2 knockouts have relatively normal forebrain development at birth, which is consistent with functional redundancy between Dlx1 and Dlx2 in this anatomic region (1,4).…”