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Microfilaments in the external surface layer of the early amphibian embryo
Abstract:
A comparison was made by transmission electron microscopy of the microfilaments in the surface layers of the early embryos of Triturus alpestris and Xenopus laevis at stages of development up to neurulation. Actin-like filaments which bound heavy meromyosin (HMM) were found in cell extracts of all stages, but were comparatively rare in the newly fertilized egg. Ten nm microfilaments were present throughout development in Xenopus, and from the mid-neurula stage in Triturus. Both kinds of microfilament were located in the circumferences of superficial ectoderm cells at the level of the apical junctions, the 10 nm microfilaments in association with desmosomes which began to develop before gastrulation in Xenopus. The accumulations of microfilaments in the apical constrictions, which form in ectoderm cells of Triturus early gastrulae when dissociated in a calcium-free medium, suggest that they are contractile elements. In the absence of such accumulations in the cell apices, the reverse curling exhibited by Xenopus ectodermal explants is attributed rather to a separation of the cells' lateral borders. Cytochalasin B (5 mug/ml) caused ectodermal explants from the early gastrulae of both species to disaggregate. With the rupture of the apical junctions there was a disorganization of the associated microfilamentous layer.
Insights
Microfilaments, including actin-like and 10 nm types, are present in early embryonic development of Triturus alpestris and Xenopus laevis. These filaments play roles in cell junctions and embryonic morphogenesis, with cytochalasin B disrupting their organization.
Area of Science:
- Developmental Biology
- Cell Biology
- Molecular Biology
Background:
- Microfilaments are crucial for cellular structure and function during embryonic development.
- Understanding the role of microfilaments in early amphibian embryogenesis provides insights into fundamental developmental processes.
Purpose of the Study:
- To compare the presence and localization of microfilaments in early embryos of Triturus alpestris and Xenopus laevis.
- To investigate the potential contractile function of microfilaments in embryonic morphogenesis.
- To examine the effect of cytochalasin B on ectodermal explants and associated microfilaments.
Main Methods:
- Transmission electron microscopy was used to examine microfilaments in embryonic tissues.
- Heavy meromyosin (HMM) binding was employed to identify actin-like filaments.
- Ectodermal explants were treated with cytochalasin B to observe cellular responses.
Main Results:
- Actin-like filaments were detected in cell extracts, increasing with developmental stage.
- 10 nm microfilaments were observed throughout development in Xenopus and from mid-neurulation in Triturus.
- Both filament types were localized at apical junctions; 10 nm filaments associated with desmosomes in Xenopus.
- Microfilament accumulations in Triturus ectoderm suggested contractile roles, contrasting with Xenopus explant behavior.
- Cytochalasin B induced disaggregation of ectodermal explants and disorganized microfilaments.
Conclusions:
- Microfilaments are integral components of the surface layers in early amphibian embryos, evolving in abundance and organization.
- Apical junctions and associated microfilaments are critical for maintaining embryonic tissue integrity.
- Differences in microfilament organization and response to cytochalasin B highlight species-specific mechanisms in early morphogenesis.