Evolutionary development of palatal bones and bmp 4 gene-ethanol interaction in cleft palate development: Insights from Mexican cavefish and zebrafish

Abstract

Craniofacial development is a tightly regulated process by several cell singalling pathways. It is therefore highly vulnerable to disturbances by genetic and environmental factors. For example ethanol exposure during pregnancy causes severe birth defects including Cleft Lip and or Palate. Zebrafish (Danio rerio) is a well-established model organism for studying craniofacial defects with remarkably high similarity to humans. Mexican tetra (Astyanax mexicanus) is another teleost and a promising model organism for evolutionary biology that exists as two morphs: pigmented-eyed surface fish and eyeless cavefish. As an adaptation to dark cave environment cavefish lost their eyes, subsequently these eye lost resulted some craniofacial structural changes in the cavefish. The first objective of my study was designed to understand the effect of early eye degeneration on parasphenoid bone in Mexican tetra. My second objective was deciphering the mechanism of bmp 4 gene-ethanol interactions on palate development. Alizarin red-bone staining, micro-CT imaging, Tartrate-resistant acid phosphatase and Alkaline Phosphate staining was conducted to understand bone ossification, articulation, and remodeling within surface and cavefish. The phenotypic effect of ethanol and Dorsomorphin (bmp 4 inhibitor) in the ethmoid plate was characterized by the alcian blue staining and data was statistically analyzed. Whole-mount in situ hybridization was used to identify the expression of bmp 4 among different treatment groups. The shape of the parasphenoid bone found to be varies amongst different eye morphs in Mexican tetra. The parasphenoid bone is straightened in cavefish and curved in surface fish. Bone remodeling activity in cavefish increased compared to the surface fish. Ethanol and Dorsomorphin affect the size of the ethmoid cartilage but the severity of the ethmoid cartilage defect increased with the combined effect of both treatments. Reduction of bmp 4 expression was observed with ethanol and combined treatment in the region of developing ethmoid cartilage. Our data confirmed the distinct morphological changes of the parasphenoid bone amongst different eye morphs of Mexican tetra fish and these changes might have evolved as adaptation to the nutrition sparse cave environment. Further ethanol does affect craniofacial bone formation and ethanol affects the bmp 4 pathway and regulate zebrafish plate development