How Unspecialized Cells Become Specialized
- Fertilization is when a sperm cell fuses with an egg cell to form a zygote, which contains the entire genetic blueprintfor a new organism.
- The zygote undergoes multiple rounds of mitosis, creating a cluster of genetically identical cells.
- Early embryonic cells are totipotent, meaning they can become any cell type in the organism or the extra-embryonic tissues (e.g., placenta).
- Cells then transition to pluripotent stem cells, which can form any cell type within the organism but not extra-embryonic structures.
Totipotent cells are unique to the earliest stages of development, while pluripotent cells persist in the inner cell mass of the blastocyst.
Differentiation: From Potential to Function
Definition
Differentiation
Differentiation is the process where pluripotent cells (unspecialized cells) develop into specialized cells with unique structures and functions.
- Although each cell has the same genome, different sets of genes are activated in different cell types, defining their structure and role (e.g., neurons, muscle fibers, red blood cells).
- Proteins or regulatory factors turn specific genes on or off, guiding the cell toward its specialized fate.
- Think of gene expression as a playlist on a music streaming app.
- Every cell has access to the same library of songs (the genome), but each cell “plays” a different playlist depending on its role in the organism.
The Role of Gradients in Gene Expression
- Gradients of signaling molecules (morphogens) diffuse through the embryo, creating varying concentrations in different regions.
- A cell’s location within the embryo (based on morphogen concentration) determines which genes are activated, influencing cell fate.
- In the fruit fly (Drosophila), gradients of morphogens such as Bicoid and Nanos regulate body segmentation.
- These gradients ensure that cells in the head region develop differently from cells in the abdomen.
