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1. Describe the phases stem cell.

2. What is the most likely type of cells that form during the first few divisions?

3 answers

  1. The phases of stem cell development can vary depending on the specific type of stem cell (embryonic stem cells, adult stem cells, etc.), but generally, the phases can be categorized into the following:

    • Self-Renewal: This is the initial phase where stem cells undergo mitotic division to produce more stem cells. They maintain their undifferentiated state and are capable of several rounds of division.

    • Differentiation: After several rounds of self-renewal, exposure to specific signals can lead stem cells to start differentiating into specialized cell types. This process involves changes in gene expression and cell behavior.

    • Commitment: Before stem cells become fully differentiated, they reach a phase of commitment where they begin to lose their pluripotency. They may go through several intermediary progenitor stages that have restricted potential to develop into specific lineages (e.g., mesodermal, ectodermal, or endodermal).

    • Maturation: In this phase, committed progenitor cells further differentiate and mature into fully functional cells (e.g., muscle cells, neurons, etc.) that exhibit the characteristics and functions specific to their type.

    • Validation: After maturation, newly differentiated cells may undergo further integrations into tissue structures and functions, ensuring that they successfully contribute to the function of the organ or system they belong to.

  2. During the first few divisions of a fertilized egg (zygote) after fertilization, the most likely type of cells that form are called blastomeres, which are totipotent cells. These cells are capable of giving rise to both the embryo and the extraembryonic tissues, such as the placenta. As the cell divisions continue (cleavage), they lead to the formation of a solid ball of cells known as a morula, and subsequently, the formation of a blastocyst, which will eventually implant into the uterine wall and develop into an embryo. The inner cell mass of the blastocyst contains pluripotent stem cells that can further differentiate into various cell types of the body.

Thanks. I was under the impression that the stages were: Totipotent stage, pluripotent, multipotent and unipotent... Why the confusion do you think?

Your understanding of stem cell stages is indeed valid and emphasizes the potency of stem cells at various points in their development. The confusion may arise from different frameworks used to describe stem cell stages, focusing on either the developmental processes or the potency.

Here’s a breakdown of the stages you mentioned, which align with the concept of potency:

  1. Totipotent Stage: This is the earliest stage, where the zygote and the first few divisions of cells (blastomeres) can differentiate into any cell type in the body, including both embryonic and extraembryonic tissues (like the placenta).

  2. Pluripotent Stage: Following the totipotent stage, cells in the inner cell mass of the blastocyst are pluripotent. They can differentiate into nearly all cell types that make up the body (all three germ layers: ectoderm, mesoderm, and endoderm) but cannot form an entire organism on their own since they lack the capacity to form extraembryonic tissues.

  3. Multipotent Stage: Cells in this stage can differentiate into a limited range of cell types, typically within a specific lineage. For example, hematopoietic stem cells are multipotent and can give rise to various types of blood cells but not other cell types like neurons or muscle cells.

  4. Unipotent Stage: Unipotent stem cells can differentiate into only one cell type but possess the ability to self-renew. For instance, skin stem cells can only become skin cells but can continually regenerate themselves.

The confusion might stem from mixing the process of differentiation (like self-renewal, differentiation, etc.) with the types of stem cells based on potency (totipotent, pluripotent, multipotent, and unipotent). The two frameworks serve different purposes: one describes the development and maturation of stem cells, while the other specifies their potential to differentiate into various cell types.

Both frameworks are valid; they just describe different aspects of stem cell biology. Understanding these distinctions can help clarify the multifaceted nature of stem cell development and differentiation.