Exogenous Sonic hedgehog protein does not rescue cultured intestine from atresia formation

Abstract

Introduction The mechanism of intestinal atresia formation remains undefined. Atresia in Fgfr2IIIb−/− mutant mouse embryos is preceded by endodermal apoptosis and involution of the surrounding mesoderm. We have observed that involution of the atretic segment is preceded by down regulation of Sonic hedgehog (SHH) in the endoderm which is a critical organizer of the intestinal mesoderm. We hypothesized that supplementation of Fgfr2IIIb−/− intestinal tracts with exogenous SHH protein prior to atresia formation would prevent involution of the mesoderm and rescue normal intestinal development. Methods In situ hybridization were performed on control and Fgfr2IIIb−/− intestinal tracts for Shh or FoxF1 between embryonic (E) day 11.5 and E12.0. Control and Fgfr2IIIb−/− intestinal tracts were harvested at E10.5 and cultured in media supplemented with FGF10 + SHH, or FGF10 with a SHH-coated bead. In situs were performed at E12.5 for Foxf1. Results Shh and Foxf1 expression were down-regulated during intestinal atresia formation. Media containing exogenous FGF10 + SHH did not prevent colonic atresia formation (involution). A SHH protein point source bead did induce Foxf1 expression in controls and mutants. Discussion 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−/− mutant embryos. Shh signal disruption is not the critical mechanism by which loss of Fgfr2IIIb function results in atresia formation.

The Role of Fibroblast Growth Factor 10 Signaling in Duodenal Atresia

“…In humans, the distribution of DA types shows similar proportions of type 1 and type 3 DA, and few cases of type 2 DA; e.g., 54% type 1, 4% type 2, and 42% type 3 DA (Khan et al, 2017). In contrast to this, when collated together, 93% of all murine DA cases reported in these studies were examples of type 3 DA, i.e., the most severe type of DA with complete discontinuity of the duodenum (Figure 1D; Fairbanks et al, 2004b;Kanard et al, 2005;Botham et al, 2012;Reeder et al, 2012b). Also, none of these studies reported any examples of type 2 DA in mice.…”

“…As will be discussed in detail in this review, murine studies have shown that interruption of the Fgf10-Fgfr2b signaling axis may result in DA in 35-75% of knockout mice (Fairbanks et al, 2004b;Kanard et al, 2005;Botham et al, 2012;Reeder et al, 2012b;Teague et al, 2018). This also supports a genetic etiology for DA in humans, however, no specific genetic cause has been demonstrated to date.…”

“…One striking feature of the DA reported in the aforementioned, seminal studies is the morphological types of DA reported in Fgf10 and Fgfr2b knockout mice (Fairbanks et al, 2004b;Kanard et al, 2005;Botham et al, 2012;Reeder et al, 2012b). In humans, the distribution of DA types shows similar proportions of type 1 and type 3 DA, and few cases of type 2 DA; e.g., 54% type 1, 4% type 2, and 42% type 3 DA (Khan et al, 2017).…”

Large intestine embryogenesis: Molecular pathways and related disorders (Review)

“…Moreover, in FGFR2IIIb -/mice with atresia, in which Fox-F1 expression is disrupted, early epithelial apoptosis and total epithelial loss seem to be the core causes of the pathophysiologic event (173). The established Fox-F1 disruption is not the most crucial problem as, even though the presence of exogenous Shh restores Fox-F1 expression that was previously disrupted, it does not alter the phenotype (174,175). Furthermore, in FGFR2IIIb -/mice, the downregulation of the expression of retinaldehyde dehydrogenase (Raldh)-2 is observed, indicating some alteration of RA signaling (176).…”

ELABELA: a novel hormone in cardiac development acting as a new endogenous ligand for the APJ receptor

“…During embryogenesis, six key signaling pathways (Wnt [3], Bmp/Nodal [4], FGF/IGF [5], Notch [6], Hedgehog [7], and Hippo [8]) have been reported to be crucial for embryonic patterning. Chng et al [1] tried to explain ELA's functions in cardiac development by activating APJ receptor.…”