Regulatory analysis of the mouseFgf3gene: Control of embryonic expression patterns and dependence upon sonic hedgehog (Shh) signalling

Abstract

Fgf3 displays a dynamic and complex expression pattern during mouse embryogenesis. To address the molecular mechanisms underlying Fgf3 expression, we used a transgenic approach to assay genomic regions from the mouse Fgf3 gene for regulatory activity. We identified an enhancer that mediates major components of embryonic expression, governing expression in the midbrain, hindbrain, surface ectoderm, dorsal roots and dorsal root ganglia (DRG), proximal sensory ganglia, and the developing central nervous system (CNS). Deletional analysis of the enhancer further delimited this regulatory activity to a 5.7-kb fragment. We have also revealed sonic hedgehog (Shh) -dependent and Shh-independent aspects of Fgf3 expression through breeding the Fgf3 reporter transgene into Shh mutants. In the absence of Shh signalling, Fgf3 reporter expression is lost in the ventral CNS, DRG, and superior cervical nerves, whereas activation of reporter expression in cranial ganglion cells is Shh independent. Moreover, detailed re-examination of the Shh phenotype revealed that Shh signalling is required for the correct development/maturation of the DRG. Developmental Dynamics 230:44 -56, 2004.

A novel method for retinoic acid administration reveals differential and dose‐dependent downregulation of Fgf3 in the developing inner ear and anterior CNS

“…A transgenic line containing lacZ under the control of this minimal Fgf3 enhancer drives expression in different regions of the developing spinal cord, at rhombomere boundaries in the hindbrain, in the anterolateral wall of the otic vesicle at the site of delaminating neuroblasts, as well as in the proximal cranial sensory ganglia ( Fig. 2A,B; Powles et al, 2004). The use of this transgenic line allows the simple and highly sensitive detection of the endogenous domains of normal Fgf3 expression, where the enhancer controls all early patterns of endogenous expression, missing only regulatory sequences governing expression normally found in the body of rhombomeres 5 and 6 (Powles et al, 2004).…”

“…2A,B; Powles et al, 2004). The use of this transgenic line allows the simple and highly sensitive detection of the endogenous domains of normal Fgf3 expression, where the enhancer controls all early patterns of endogenous expression, missing only regulatory sequences governing expression normally found in the body of rhombomeres 5 and 6 (Powles et al, 2004). RA has previously been implicated in the regulation of Fgf3 in the developing inner ear, since RT-PCR of mRNA from dissected 9.5-dpc otic vesicles indicates a diminution of Fgf3 expression following gavage administration of RA (Liu et al, 2008).…”

“…However, the whole embryo appears rather delayed using this dose, which complicates this analysis. Fgf3 expression 0.5 dpc earlier than that analysed in Figure 3 is normally more broad but begins to become more focused to anterior regions as development proceeds at 9.5 dpc (see Powles et al, 2004). Since Fgf3 expression did not appear downregulated at this increased dose, this prompted us to examine Fgf3 reporter expression following an additional day of in utero development in order to exclude differences due to any developmental delay.…”

Differential requirements for Fgf3 and Fgf8 during mouse forebrain development

“…To monitor Fgf3 expression during forebrain development in the mouse embryo between E7.5 until E12.5 we used a Fgf3/lacZ reporter transgene previously described (Powles et al, 2004a). Fgf3 expression is first detected at E7.75 in the ANR (Fig.…”

“…The following mouse lines used in this study have been described previously: Fgf3 Ϫ/Ϫ knockout mutants (Alvarez et al, 2003), mutants carrying a conditional (Fgf8 flox ) or a null allele (Fgf8 d2,3 ) for Fgf8 (Meyers et al, 1998), mouse lines in which cre has been targeted to the Foxg1 locus (BF-1) (Hebert and McConnell, 2000), and transgenic mice which express lacZ under the control of Fgf3 regulatory sequences (Powles et al, 2004b). To obtain mouse mutants that lacked Fgf8 expression in the telencephalon (Fgf8 TelKO ), we crossed animals carrying a Fgf8 null allele and the Foxg1-Cre transgene (Fgf8 d2,3/ϩ ;Foxg1 Cre/ϩ ) with animals carrying a conditional Fgf8 allele (Fgf8 flox/flox ) to obtain Fgf8 flox/d2,3 ; Foxg1 Cre/ϩ (Fgf8 TelKO ) mutants as previously described (Storm et al, 2003).…”