Tails of the unexpected: palatal medial edge epithelium is no more specialized than other embryonic epithelium

Genetic background influences the capacity for medial edge epithelium disintegration and phenotype of cleft palate in TGFβ3 knockout mice

OBJECTIVES

Cleft palate is a frequent congenital craniofacial malformation of unknown etiology. Transforming growth factor (TGF) β3 is required for palatal shelf fusion. Although TGFβ3 knockout (KO) mice are widely used mouse models for cleft palate, cleft palate phenotypes differ among these mice. This study aimed to determine the effects of genetic background on the cleft palate phenotype in mice.

METHODS

We produced TGFβ3 KO congenic mouse strains with five different genetic backgrounds. The phenotypes of the congenic strains were determined by visual examination. The capacity for disintegration of the medial edge epithelium (MEE) and basement membrane (BM) of palatal shelves of all five mouse strains was analyzed by using immunofluorescence staining after single palatal shelf suspension culture. The relationship between phenotype and disappearance of the MEE and BM was analyzed.

RESULTS

Although the five congenic strains carried the same defective Tgfb3 gene, the fetal palate phenotypes differed among strains. The loss of the MEE cells and BM also differed with the genetic background, and the degree of such loss correlated with the cleft palate phenotype.

CONCLUSIONS

The cleft palate phenotype in mice is influenced by the genetic background, which governs the capacity for MEE and BM disintegration.

Chemokine Signaling during Midline Epithelial Seam Disintegration Facilitates Palatal Fusion

Disintegration of the midline epithelial seam (MES) is crucial for palatal fusion, and failure results in cleft palate. Palatal fusion and wound repair share many common signaling pathways related to epithelial-mesenchymal cross-talk. We postulate that chemokine CXCL11, its receptor CXCR3, and the cytoprotective enzyme heme oxygenase (HO), which are crucial during wound repair, also play a decisive role in MES disintegration. Fetal growth restriction and craniofacial abnormalities were present in HO-2 knockout (KO) mice without effects on palatal fusion. CXCL11 and CXCR3 were highly expressed in the disintegrating MES in both wild-type and HO-2 KO animals. Multiple apoptotic DNA fragments were present within the disintegrating MES and phagocytized by recruited CXCR3-positive wt and HO-2 KO macrophages. Macrophages located near the MES were HO-1-positive, and more HO-1-positive cells were present in HO-2 KO mice compared to wild-type. This study of embryonic and palatal development provided evidence that supports the hypothesis that the MES itself plays a prominent role in palatal fusion by orchestrating epithelial apoptosis and macrophage recruitment via CXCL11-CXCR3 signaling.

Memory encoded throughout our bodies: molecular and cellular basis of tissue regeneration

When a sheep loses its tail, it cannot regenerate it in the manner of lizards. On the other hand, it is possible to clone mammals from somatic cells, showing that a complete developmental program is intact in a wounded sheep's tail the same way it is in a lizard. Thus, there is a requirement for more than only the presence of the entire genetic code in somatic cells for regenerative abilities. Thoughts like this have motivated us to assemble more than just a factographic synopsis on tissue regeneration. As a model, we review skin wound healing in chronological order, and when possible, we use that overview as a framework to point out possible mechanisms of how damaged tissues can restore their original structure. This article postulates the existence of tissue structural memory as a complex distributed homeostatic mechanism. We support such an idea by referring to an extremely fragmented literature base, trying to synthesize a broad picture of important principles of how tissues and organs may store information about their own structure for the purposes of regeneration. Selected developmental, surgical, and tissue engineering aspects are presented and discussed in the light of recent findings in the field. When a sheep loses its tail, it cannot regenerate it in the manner of lizards. On the other hand, it is possible to clone mammals from somatic cells, showing that a complete developmental program is intact in a wounded sheep's tail the same way it is in a lizard. Thus, there is a requirement for more than only the presence of the entire genetic code in somatic cells for regenerative abilities. Thoughts like this have motivated us to assemble more than just a factographic synopsis on tissue regeneration. As a model, we review skin wound healing in chronological order, and when possible, we use that overview as a framework to point out possible mechanisms of how damaged tissues can restore their original structure. This article postulates the existence of tissue structural memory as a complex distributed homeostatic mechanism. We support such an idea by referring to an extremely fragmented literature base, trying to synthesize a broad picture of important principles of how tissues and organs may store information about their own structure for the purposes of regeneration. Selected developmental, surgical, and tissue engineering aspects are presented and discussed in the light of recent findings in the field.