The Role Of Wnt Signaling Pathway In The Ventral Body Wall Development And Bone Marrow Stem Cell Differentiation

Ventral body wall abnormalities are common human birth defects present in about one out of every 2000 live births, which can be categorized as ectopia cordis, bladder exstrophy, gastroschisis, omphalocele, prune belly syndrome. The pathological cause of ventral body wall abnormalities is very poorly understood due to rare animal model.To investigate the role of Wnt in ventral body wall development, Msx2-Cre was used to inactivate Wntless to block Wnts secretion in the ectoderm of the ventral body wall. The homozygous Msx2-Cre;Wlsc/c embryos exhibited deformities in ventral body wall development. In addition, genitalia formation was disrupted in the Msx2-Cre;Wlsc/c embryos. The ventral body wall abnormalities indicated agenesis of the secondary ventral body wall. Ectodermal loss of Wntless impaired myoblast migration and differentiation. In addition, dermis specification was perturbed by the loss of ectodermal Wntless. Ablation of epithelial β-catenin has no similar effect on ventral body wall development. No remarkable defect in ventral body wall was detected in Wnt5 a null mice. Wnts could act by autocrine and paracrine manners. These results indicated that ectodermal Wnt signaling determine the mesodermal cells fate. Wnt-mediated epithelial-mesenchymal signaling plays an important role in the development of ventral body wall.X-gal staining for TOPGAL mice showed that the canonical Wnt signaling pathway was activated in the ventral body wall. Diminished X-gal staining was observed in ventral epithelium of Msx2-Cre;Wlsc/c;Topgal relative to Wlsc/c;Topgal embryos indicating the down regulation of canonical Wnt signaling activity. The whole mount and section in situ hybridization indicated Pitx2 m RNA was affected in the development of ventral body wall. The Wnt-Pitx2 s ignaling pathway has been reported to regulate limb and somite myogenes is. Therefore, the activity of the Wnt/β-catenin-Pitx2 axis was impaired in the mutant body wall, which mainly accounted for the defects in ventral musculature formation.In our study, specific inactivation of Wntless in the mouse abdomina l ectoderm led to typical prune belly syndrome(PBS)-like phenotypes, in accordance with limb-body wall complex(LBWC). Msx2-Cre;Wlsc/c mice can be used as a model of etiology of some clinical vetral body wall abnormalities. Together, we present that epithelial-mesenchymal signaling is a potential theory that accounts for ventral body wall defects, providing a better theory basis for clinical treatment.In addition, we also studied the role of Wnt signaling pathway in the bone marrow stem cell self-renewal and differentiation. There are two types of stem cell population in the adult bone marrow, MSC and HSC, The maintenance of the stem cell properties is critical for the homeostasis and normal function of tissues. Their self-renewal and differentiation is tightly controlled by the niches in bone marrow. It is unclear whether Wnt signaling from MSC is involved in mediating bone marrow stem cell self-renewal and differentiation.To test this possibility, we inactivate Wntless by Nestin-Cre mice. We found that blocking of Wnt signaling promoted MSC self-renewal. MSC from Nestin-Cre;Wlsc/c showed enhanced adipogenic differentiation at the expense of osteoblast differentiation. MSC can contribute to HSC niche to mediate MSC self-renewal and differentiation. The Nestin-Cre;Wlsc/c mice displayed defective B-cell lymphopoiesis and increased T cells in the bone marrow. The FACS analyses showed that the cellularity and percentage of total B220~+ B cell lineages, pro-B, pre-B, and immature B cells were decreased in the mutant bone marrow compared to the controls. Meanwhile, the percentage of CD4~+ and CD8~+ T cells was enriched in the mutant bone marrow and spleen, which were mostly CD62L~+CD44- naive T cells. In addition, the CD62L~+CD44~+ central memory T cells were also relatively enriched in the bone marrow of Nestin-Cre;Wlsc/c mice.These observations suggested that Wnt signaling from MSC regulated MSC self-renewal and differentiation, it also contribute to regulate HSC differentiation as a niche component. These findings are instructive for functional analysis and clinical application of bone marrow stem cells.