All cells have an identical genome. How do cell differentiation and morphogenesis occur?
Through gene regulation, a combination of cytoplasmic determinants and inductive signals.
Cytoplasmic determinants are present in the egg prior to fertilization.
Inductive signals come from other embryonic cells (including paracrine signaling, cell-cell recognition)
What are cytoplasmic determinants?
Cytoplasmic determinants include mRNA, proteins, and organelles present in the egg prior to fertilization. Cytoplasmic determinants are distributed unevenly in the cytoplasm, and regulate gene expression during cell differentiation.
What is induction?
Induction describes the changes in the target cell caused by intercellular signaling (paracrine signaling, cell-cell recognition).
What is cell determination?
Determination describes the changes at the molecular level within a cell that lead to the differentiation of a cell. Once the cell undergoes determination, it can no longer divide into a different type of cell.
What is cell differentiation?
Cell differentiation happens when cells express genes for tissue-specific proteins. This often begins with the activation of a master regulatory gene which produces a transcription factor as a product, activating other genes and secondary transcription factors. This is an example of coordinately controlled genes (they are controlled by a single "switch")
What is apoptosis?
Apoptosis is the self-destruction of a cell. This is important in vertebrate development in the formation of certain structures, such as the nervous system or fingers on the hand. The cell breaks into vesicles (blebs) in a process called blebbing.
Apoptosis is triggered by signal transduction pathways.
What is pattern formation?
Pattern formation describes the processes that contribute to the organization within a developing embryo. Pattern formation is controlled by cytoplasmic determinants and inductive signals.
What are homeotic genes?
Homeotic genes in the embryo control pattern formation in the late embryo, larva, and adult. Distinct from maternal effect genes/egg-polarity genes, which are part of the mother's genetic code.
What are maternal effect genes/egg-polarity genes?
Maternal effect genes are part of the mother's genome and produce cytoplasmic determinants present in unfertilized eggs. These cytoplasmic determinants and their products, called morphogens, help establish the axes of the future organism.
How can pattern formation play a part in the process of evolution?
Mutations in egg-polarity genes (maternal effect genes) might influence the evolution of a species by creating novel body shapes.