Background
The mechan
ism of
intest
inal atres
ia format
ion rema
ins undef
ined. Atres
ia
in
fibroblast growth factor receptor 2IIIb (Fgfr2IIIb鈭?鈭?/em>) mutant mouse embryos
is preceded by endodermal apoptos
is and
involut
ion of the surround
ing mesoderm. We have observed that
involut
ion of the atret
ic segment
is preceded by the downregulat
ion of Son
ic hedgehog (SHH)
in the endoderm, wh
ich
is a cr
it
ical organ
izer of the
intest
inal mesoderm. We hypothes
ized that supplementat
ion of
Fgfr2IIIb鈭?鈭?/em> intest
inal tracts w
ith exogenous SHH prote
in before atres
ia format
ion would prevent
involut
ion of the mesoderm and rescue normal
intest
inal development.
Methods
In situ hybridization was performed on control and Fgfr2IIIb鈭?鈭?/em> intestinal tracts for Shh or forkhead box protein F1 (FoxF1) between embryonic (E) day 11.5 and E12.0. Control and Fgfr2IIIb鈭?鈭?/em> intestinal tracts were harvested at E10.5 and cultured in media supplemented with fibroblast growth factor (FGF) 10聽+聽SHH, or FGF10 with a SHH-coated bead. In situ hybridization was performed at E12.5 for Foxf1.
Results
SHH and Foxf1 expression were downregulated during intestinal atresia formation. Media containing exogenous FGF10聽+聽SHH did not prevent colonic atresia formation (involution). A SHH protein point source bead did induce Foxf1 expression in controls and mutants.
Conclusions
Shh and Foxf1 expression are disrupted in atresia formation of distal colon, thereby serving as potential markers of atretic events. Application of exogenous SHH (in media supplement or as a point source bead) is sufficient to induce Foxf1 expression, but insufficient to rescue development of distal colonic mesoderm in Fgfr2IIIb鈭?鈭?/em> mutant embryos. Shh signal disruption is not the critical mechanism by which loss of Fgfr2IIIb function results in atresia formation.
