Inactivation of FGF8 in early mesoderm reveals an essential role in kidney development

Abstract

To bypass the essential gastrulation function of Fgf8 and study its role in lineages of the primitive streak, we have used a new mouse line,T-Cre, to generate mouse embryos with pan-mesodermal loss of Fgf8expression. Surprisingly, despite previous models in which Fgf8 has been assigned a pivotal role in segmentation/somite differentiation, Fgf8 is not required for these processes. However, mutant neonates display severe renal hypoplasia with deficient nephron formation. In mutant kidneys, aberrant cell death occurs within the metanephric mesenchyme (MM),particularly in the cortical nephrogenic zone, which provides the progenitors for recurring rounds of nephron formation. Prior to mutant morphological changes, Wnt4 and Lim1 expression, which is essential for nephrogenesis, is absent in MM. Furthermore, comparative analysis of Wnt4-null homozygotes reveals concomitant downregulation of Lim1 and diminished tubule formation. Our data support a model whereby FGF8 and WNT4 function in concert to induce the expression of Lim1 for MM survival and tubulogenesis.

Conditional inactivation of Fgfr1 in mouse defines its role in limb bud establishment, outgrowth and digit patterning

“…We found no difference in phenotype between cre;Fgfr1 null/co or cre;Fgfr1 co/co , and we therefore refer to these genotypes as Tcre;Fgfr1 or Shhcre;Fgfr1, depending on which Cre-expressing line was used. Tcre is generated through a transgenic approach using a 500 bp T (brachyury) promoter (Clements et al, 1996) driving Cre expression in the primitive streak-derived mesoderm lineages starting at E7.5 (Perantoni et al, 2005). By mating Tcre line to a cre activity reporter line R26R (Soriano, 1999), we found that at E8.5 and E10.0, Tcre is active in the LPM posterior to the heart, including the LBM (Fig.…”

“…Upon Cremediated recombination of this allele, Fgfr1 exons 8-14 are deleted, resulting in a null allele in which both the IIIb and IIIc isoforms are inactivated. We generated two Fgfr1 mutants using two Cre-expressing lines, the Tcre transgenic line (Perantoni et al, 2005) and mice carrying the Shh cre allele (Harfe et al, 2004). We found no difference in phenotype between cre;Fgfr1 null/co or cre;Fgfr1 co/co , and we therefore refer to these genotypes as Tcre;Fgfr1 or Shhcre;Fgfr1, depending on which Cre-expressing line was used.…”

“…Mice carrying a conditional allele of Fgfr1 (Fgfr1 co ) (Xu et al, 2002) were mated to either Tcre line (Perantoni et al, 2005) or Shh cre (Harfe et al, 2004) allele to generate Tcre;Fgfr1 and Shhcre;Fgfr1 mutant embryos, respectively. Offspring were genotyped using the following PCR primer pairs: for Cre, 5Ј-TGATGAGGTTCGCAAGAACC-3Ј and 5Ј-CCATGAGTGAACGAACCTGG-3Ј; for Fgfr1, 5Ј-CTG-GTATCCTGTGCCTATC-3Ј and 5Ј-CAATCTGATCCCAAGAC-CAC-3Ј.…”

FGF4 and FGF8 comprise the wavefront activity that controls somitogenesis

“…Moreover, manipulation of downstream components implicated FGF signaling in determination front positioning (6). However, mouse embryos lacking Fgf8 in the PSM revealed that Fgf8 is not required for somitogenesis (7). Furthermore, mice homozygous for null mutations in other FGF ligand genes (Fgf3, Fgf5, Fgf15, Fgf17, and Fgf18) expressed in the PSM also show no early somitogenesis defects, or die before somitogenesis (Fgf4) (7)(8)(9).…”

Renal organogenesis

“…6,7 The process of MET is triggered via canonical Wnt signaling initiated by the secretion of Wnt9b from the ureteric tip, 8,9 which in turn upregulates Fgf8 and Wnt4. 10,11 Noncanonical Wnt4 signaling, in turn, initiates renal vesicle formation. 12,13 While we have been aware of these interactions for some 50 years, 14 our understanding of the molecular basis of these events and the lineage relationships between different cell types in the kidney has increased dramatically in the last decade ( Fig.…”