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Effects of L-phenylalanine on somite formation in the early chick embryo
Insights
L-phenylalanine exposure during early chick embryo development causes imperfect somite segmentation. This disruption, characterized by unsegmented mesoderm blocks, is time-dependent and linked to suppressed yolk granule decomposition.
Area of Science:
- Developmental biology
- Embryology
- Cell biology
Background:
- Somitogenesis is a critical process in vertebrate embryonic development.
- Proper segmentation of somites is essential for forming axial structures.
- Disruptions in somitogenesis can lead to developmental abnormalities.
Purpose of the Study:
- To investigate the effects of L-phenylalanine exposure on chick embryo somitogenesis.
- To determine the temporal correlation between L-phenylalanine treatment and somite segmentation defects.
- To explore the underlying cellular mechanisms of L-phenylalanine-induced developmental disturbances.
Main Methods:
- In ovo and in vitro treatment of chick embryos with L-phenylalanine at specific developmental stages (Hamburger & Hamilton stages 3-9).
- Analysis of somite segmentation, including the formation of unsegmented somite mesoderm blocks.
- Mitotic index assessment, autoradiography with tritiated L-phenylalanine, and electron microscopy.
- In vitro experiments to assess L-phenylalanine diffusion through the vitelline membrane.
Main Results:
- L-phenylalanine treatment resulted in imperfectly segmented somites (somite blocks) in a time-dependent manner.
- Early treatment (12-21 h) affected somite pairs 1-5, while later treatment (24-30 h) affected pairs 5-10.
- No differences in mitotic indices or L-phenylalanine labeling were observed between normal and affected somites.
- Electron microscopy showed suppressed microvilli formation in unsegmented mesoderm blocks, likely due to impaired yolk granule decomposition.
Conclusions:
- L-phenylalanine exposure disrupts chick embryo somitogenesis, leading to the formation of unsegmented mesoderm blocks.
- The timing of L-phenylalanine exposure correlates with the location of segmentation defects.
- The mechanism involves suppressed yolk granule decomposition and potentially altered cell surface morphology.
- L-phenylalanine diffusion through the vitelline membrane is slow, suggesting localized effects or prolonged exposure.
Abstract:
Chick embryos were treated in ovo and in vitro with L-phenylalanine from the intermediate streak stage (Hamburger & Hamilton stage 3, 12-13 h of incubation) to the 7-somite stage (H & H stage 9, 29-33 h of incubation). Treatment in ovo resulted in a large number of embryos developing somite blocks, i.e. imperfectly segmented somites. In embryos treated at an early developmental stage (12-21 h of incubation), the blocks of unsegmented somite mesoderm occurred mostly in the somite pairs 1-5, whereas treatment that began at a later stage (24-30 h of incubation) caused blocks in the somite pairs 5-10, i.e. the appearance of blocks of unsegmented somite mesoderm is correlated in time with the onset of the treatment. No difference regarding mitotic indices could be distinguished between normally segmented somites and blocks of unsegmented somite mesoderm. Autoradiography based on tritiated L-phenylalanine showed no regional differences in labelling of the chick embryo body. Electronmicroscopical observations indicate a slightly suppressed formation of microvilli in the cells of the unsegmented mesoderm blocks compared with cells in normally segmented somites. The observed disturbances are probably caused by a suppressed yolk granule decomposition in the developing somite cells. The experiments in vitro support the findings in the in ovo material; at the same time, they reveal an unexpectedly slow diffusion of L-phenylalanine through the vitelline membrane.