Final answer:
B. they never differentiate into muscle cells in a normally developing animal. Fibroblast cells serve as a model for studying muscle differentiation due to their role in connective tissue formation, not because they differentiate into muscle cells. They are multipotent cells derived from mesoderm, and muscle differentiation is regulated by specific transcription factors that govern gene expression.
Step-by-step explanation:
Fibroblast cells are a model system for studying muscle differentiation because they can differentiate into a range of connective tissues but not typically into muscle cells in a normally developing animal. They are not totipotent, as this characteristic is exclusive to the zygote, which can give rise to all cells in the body. Instead, fibroblasts are derived from the mesoderm and are involved in forming connective tissues such as collagen and extracellular matrix components.
Different cell types arise from varying levels of stem cells: totipotent, pluripotent, and multipotent. Totipotent stem cells, like the zygote, can differentiate into any cell type. Pluripotent stem cells can become any tissue type but cannot support full organismal development. Multipotent cells, which include fibroblasts, have a more limited differentiation capacity, geared towards a related group of cells— in the case of fibroblasts, those involved in connective tissue, but not muscle or nervous tissues.
During development, specific transcription factors govern the differentiation process, dictating which genes are expressed to give cells their unique characteristics. For example, myoblasts, which are muscle-forming stem cells, have a distinctive expression pattern driven by transcription factors which enable them to form muscle tissue.