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From frog eggs to humans: How to uncover the mysteries of the primitive streak in embryonic development?
A structure called the primitive streak plays a crucial role in the development of frog eggs into human embryos. The formation of this structure marks the development of the early embryo and has a fundamental influence on the shape and tissue structure of the embryo. This article aims to explore the formation process of the primitive streak, its role in embryonic development, and how these processes vary and resemble each other in different species.
Formation of original stripes
During early embryonic development, the primitive streak is a midline structure located on the dorsal side of the embryo, initially forming at the caudal (posterior) end of the embryo. At the site of the upcoming primitive streak, the inner cells organize into an area of active proliferation, preparing for future cell entry and migration.
The formation of the primitive streak marks bilateral symmetry and the formation of different germ layers within the embryo.
During the embryonic stage of 12 to 17 days, the primitive streak becomes more distinct and begins to recede into the tail, forming a mass of cells called the tail bud, a process that also promotes the development of the notochord. The notochord is formed to provide support and signaling for future vertebrate development.
Differences among species
The primitive streak and its corresponding structure have different names in different species. For example, in amphibians, the structure corresponding to the primitive streak is the blastopore. In bird embryos, the corresponding organ is called Hensen's node, a static structure that marks the origin of the primitive streak. These differences involve more than just names; they also reflect the evolutionary adaptations of different species during embryonic development.
Regulation of signaling pathways
The formation of primitive streaks involves the coordinated action of multiple signaling pathways. In the development of chicken embryos, signaling factors such as Vg1, Nodal, Wnt8C, FGF8, and Chordin need to be activated at the site of formation to promote the formation of the primitive streak. In addition, related transcription factors such as Brachyury and Goosecoid also play an indispensable role.
The interaction between these signaling pathways is key to the formation of stable primitive streaks.
Specifically, Nodal is a key factor affecting the shape and position of the original stripes. In mouse embryos, loss of Nodal signaling leads to organ loss and failure of normal embryonic development.
Reflection on Ethics
As more is learned about embryonic development, the question of how the primitive streak forms has come into ethical discussion. Many experts believe that research on human embryos before the primitive streak is allowed because this process marks the formation of a unique human being. The laws of some countries stipulate that the survival time of a developing human embryo does not exceed 14 days.
This makes us wonder: What is the relationship between scientific progress and ethical boundaries? And how should we define when an ethical boundary becomes inviolable in the process of exploring the mysteries of life?
