Retinoic acid receptor signaling regulates choroid fissure closure through independent mechanisms in the ventral optic cup and periocular mesenchyme

Abstract

Retinoic acid receptor (RAR) signaling is required for morphogenesis of the ventral optic cup and closure of the choroid fissure, but the mechanisms by which this pathway regulates ventral eye development remain controversial and poorly understood. Although previous studies have implicated neural crest-derived periocular mesenchyme (POM) as the critical target of RA action in the eye, we show here that RAR signaling regulates choroid fissure closure in zebrafish by acting on both the ventral optic cup and the POM. We describe RAR-dependent regulation of eight genes in the neuroepithelial cells of the ventral retina and optic stalk and of six genes in the POM and show that these ventral retina/optic stalk and POM genes function independently of each other. Consequently, RAR signaling regulates ventral eye development through two independent, nonredundant mechanisms in different ocular tissues. Furthermore, the identification of two cohorts of genes implicated in ventral eye morphogenesis may help to elucidate the genetic basis of ocular coloboma in humans.

Fgf-Signaling-Dependent Sox9a and Atoh1a Regulate Otic Neural Development in Zebrafish

“…In fact, a slight reduction of SAG area was also evident in atoh1b morphants (Table 4), reinforcing the idea that atoh1b is genetically upstream of atoh1a. Interestingly, in Atoh1-null mice, fewer afferent fibers from SAG were found to innervate sensory epithelia from embryonic day 12.5 to 18.5 (Fritzsch et al, 2005). Because SAG afferent neurons send a single axon toward their targets, it is likely that correspondingly SAG cell body number was also reduced in these mice (Fritzsch et al, 2005;.…”

“…In situ hybridization and immunostaining were performed as described previously (Westerfield, 2007). The following probes and antibodies were used: neurod (Korzh et al, 1998), atoh1a (Millimaki et al, 2007, atoh1b (Millimaki et al, 2007), sox9a (Yan et al, 2002), tlx2 (Langenau et al, 2002), eya2 (Lupo et al, 2011), anti-GFP (1:500; rabbit or mouse; Invitrogen), anti-HuC/D (1:500; mouse; Invitrogen), and anti-MyoVI (1:200, rabbit; Proteus Biosciences).…”

“…Sox9 is involved in neural differentiation within the CNS (Scott et al, 2010;Martini et al, 2013), but whether it also promotes neurogenic development in the peripheral nervous system is unknown. Zebrafish atoh1a marks the prospective maculae from otic specification stages and indicates hair cell differentiation (Chen et al, 2002;Adolf et al, 2004;Millimaki et al, 2007), the process called otic sensorigenesis (Maier et al, 2014). It is worth noting that Atoh1 is expressed at low levels in SAG/hair cell precursors of mouse otocyst , implicating additional involvement of Atoh1 in otic neurogenesis.…”

“…Zebrafish otic neurogenesis, referring to otic neuronal specification and differentiation (Maier et al, 2014), occurs during a relatively long developmental period. After initial specification and differentiation of otic neuroblasts at the early to midsegmentation stages, migration of neuroblasts begins at the 22 hours postfertilization (hpf) and ends at approximately the 42 hpf stage in zebrafish (Haddon and Lewis, 1996;Whitfield et al, 2002).…”

Exome sequencing in developmental eye disease leads to identification of causal variants in GJA8, CRYGC, PAX6 and CYP1B1

“…CYP1B1 can contribute to retinoic acid synthesis in embryonic development, 35 and retinoic Table 3 Other variants lacking appropriate segregation-allele frequencies in public databases, conservation and prediction categories acid receptor signalling regulates choroid fissure closure. 36 The presence of variation in two genes, GDF3 and CYP1B1, which may modulate choroid fissure closure, may be relevant as contributing factors to the disease in Patient 11 (Family 11, II.1). Patients 9 (Family 9, II.1) and 11 (Family 11, II.1), both with coloboma/microphthalmia, also had rare heterozygous variants in BFSP1, which encodes a beaded filament lens protein.…”