Ldb1 and Rnf12-dependent regulation of Lhx2 controls the relative balance between neurogenesis and gliogenesis in retina

Abstract

Precise control of the relative ratio of retinal neurons and glia generated during development is essential for visual function. We show that , which encodes a LIM-homeodomain transcription factor essential for specification and differentiation of retinal Müller glia, also plays a crucial role in the development of retinal neurons. Overexpression of with its transcriptional co-activator triggers cell cycle exit and inhibits both Notch signaling and retinal gliogenesis./ overexpression also induces the formation of wide-field amacrine cells (wfACs). In contrast, , which encodes a negative regulator of LDB1, is necessary for the initiation of retinal gliogenesis. We also show that Lhx2-dependent neurogenesis and wfAC formation requires and , and that Lhx2 is necessary for their expression, although overexpression of/ does not elevate expression of these proneural bHLH factors. Finally, we demonstrate that the relative level of the LHX2-LDB1 complex in the retina decreases in tandem with the onset of gliogenesis. These findings show that control of function by and underpins the coordinated differentiation of neurons and Müller glia in postnatal retina.

Necessity and Sufficiency of Ldb1 in the Generation, Differentiation and Maintenance of Non-photoreceptor Cell Types During Retinal Development

“…From P8 and beyond, it was restricted only to the INL and GCL ( Figures 1G,H ). The observed pattern of Ldb1 in situ hybridization signal was similar to that of a previous study which also included stages E14, E16 and P0 ( de Melo et al, 2018 ), except that the signal was incompletely downregulated from the ONL of late postnatal retinas in the previous work whereas we saw a near complete downregulation ( Figures 1G,H ). Ldb1 protein displays an expression pattern quite similar to that of its RNA.…”

“…While this project was ongoing, two reports studying the LDBs in the retina were published recently ( Gueta et al, 2016 ; de Melo et al, 2018 ). Despite some similar and consistent discoveries made in our and previous studies, our current work provides a hugely different set of data, gains several novel insights, makes several clarifications, and emphasizes on many new aspects:…”

“…The Six3-Cre line offers the advantage for us to evaluate the whole-range of retinal defects resulting from Ldb1 inactivation such as optic nerve hypoplasia and retinal detachment which were unseen in the prior study; (3) We investigated the profound visual function loss in adult Ldb1 null mice by ERG, an advantage afforded by the Six3-Cre line, which was untouched in the previous work; (4) We demonstrated by a gain-of-function approach the sufficiency of Ldb1 in promoting the differentiation of all non-photoreceptor cell types at the cost of photoreceptors. The previous overexpression study ( de Melo et al, 2018 ) focused on Müller cells and thus barely checked effects on other cell types. Moreover, forced expression of Ldb1 was found to inhibit gliogenesis in the prior study ( de Melo et al, 2018 ); and (5) In contrast to the previous conclusion that Ldb2 is sufficient to substitute Ldb1 in RPCs and Müller cells ( Gueta et al, 2016 ), our data have demonstrated that Ldb1 has unique functions in these two types of cells that cannot be completely compensated for by Ldb2.…”

“…The previous overexpression study ( de Melo et al, 2018 ) focused on Müller cells and thus barely checked effects on other cell types. Moreover, forced expression of Ldb1 was found to inhibit gliogenesis in the prior study ( de Melo et al, 2018 ); and (5) In contrast to the previous conclusion that Ldb2 is sufficient to substitute Ldb1 in RPCs and Müller cells ( Gueta et al, 2016 ), our data have demonstrated that Ldb1 has unique functions in these two types of cells that cannot be completely compensated for by Ldb2. Several lines of evidence including RNA-seq, qRT-PCR and immunostaining results all indicate that Ldb1 inactivation causes aberrant generation of supernumerary amacrine and horizontal cells as a result of precocious differentiation of early RPCs.…”

SCF/SCFR signaling plays an important role in the early morphogenesis and neurogenesis of human embryonic neural retina

“…The consequences of overactivation and inhibition of SCF/SCFR signaling differed between neurogenesis and gliogenesis in the central NR. These data suggest that SCF/SCFR signaling may be involved in modulation of an intrinsic retinal developmental gene such as Lhx2 (de Melo et al, 2018). Other classic pathways of neural development, such as Wnt, Notch and Hedgehog signaling, may also crosstalk with SCF/SCFR signaling, as reported in other organ development or disease pathophysiology (Ahmad et al, 2004).…”