Molecular Biology Lecture 2 Part 2 PDF

◦Explain the differences in gene transcription during and immediately after mitosis and why these newer findings were unexpected 2. Differences in Gene Transcription During and Immediately After Mitosis: During Mitosis: ○ Chromatin Condensation: During mitosis, chromatin...

◦Explain the differences in gene transcription during and immediately after mitosis and why these newer findings were unexpected 2. Differences in Gene Transcription During and Immediately After Mitosis: During Mitosis: ○ Chromatin Condensation: During mitosis, chromatin is highly condensed into chromosomes, and transcriptional activity is generally suppressed. The mitotic phase is characterized by a global reduction in gene transcription due to the tight packaging of DNA, which limits the accessibility of transcriptional machinery to DNA. Immediately After Mitosis (Cytokinesis and G1 Phase): ○ Transcriptional Reawakening: After mitosis, cells undergo a period of transcriptional reactivation. This is a critical phase where cells resume the transcription of genes required for cell growth and preparation for the next cell cycle. New findings have shown that certain genes are transcriptionally reactivated immediately after mitosis, contrary to previous expectations that transcription would be largely silent during this transition. ○ Unexpected Findings: Recent research has revealed that specific transcription factors and chromatin remodeling complexes are actively involved in reestablishing transcriptional programs shortly after mitosis. This finding was unexpected because it was previously believed that cells required a longer period of chromatin relaxation and reorganization before transcription could resume. The rapid reactivation of transcription highlights the cell's ability to quickly adapt and prepare for subsequent cell cycle phases. ◦Explain the role of transcription factors in cellular differentiation and morphogenesis - Terminal differentiation contributes to cell behaviors including motility and proliferation - Differentiation is caused by and results in different patterns of gene expression - Differentiated cells frequently do not have the same proliferative potential as their naïve or stem cell counterparts - The patterns of expression of key genes associated with cell division and proliferation are different - Differentiated cells may also exhibit reduced or altered responsiveness to growth signaling  6. Evaluate the role of gene expression, cellular programming, and regulation of the cell cycle in maintaining pluripotency vs commitment and differentiation and assess the consequence for changes in gene activity on pluripotency or differentiation ◦Define: totipotent, pluripotent, embryonic stem cell, determination, specialization, differentiation, and morphogenesis - Done ◦Summarize the broad steps associated with morphogenesis 1. Fertilized ovum 2. Multiple Embryos (zygote up to early blastomeres 8-cell stage) a. totipotent cells. 3. Single embryo in early stages of forming 3 germ layers a. Pluripotent cells i. Embryonic Stem Cells ii. Refers to a cell's ability to differentiate into almost all cell types, except for extraembryonic tissues. 4. Organogenesis a. Committed cells i. Cells are committed to certain fates, building blocks of vital organs 5. Formation of structures a. Differentiation b. Maturation i. All cells ◦Identify when maternal control shifts to zygotic control Shift from Maternal Control to Zygotic Control Maternal Control: During early embryonic development, gene expression is largely controlled by maternal mRNAs and proteins deposited in the egg. This stage involves maternal contributions to regulate initial cell divisions and development.  Zygotic Control: Shifts to zygotic control typically occur at the mid-blastula transition (MBT). At this point, the embryo begins to use its own genome for transcription and regulation, marking the transition from maternal to zygotic control of development. ◦Identify genes associated with pluripotency Genes Associated with Pluripotency (transcription factors) Oct4 (POU5F1): A key transcription factor in maintaining pluripotency. Sox2: Works alongside Oct4 to regulate pluripotency. Nanog: A transcription factor crucial for maintaining the undifferentiated state of ESCs. Klf4: Another transcription factor involved in maintaining pluripotency. ◦List the differences between pluripotent cells and differentiated cells in terms of cell cycle stage lengths Differences Between Pluripotent Cells and Differentiated Cells in Terms of Cell Cycle Stage Lengths Pluripotent Cells: ○ Shorter G1 and G2 phases ○ Longer S phase ○ Shorter overall cell cycle They divide rapidly to support the development of the embryo. ○ Altered phosphorylation of Rb and/or altered timing of the phosphorylation Differentiated Cells: ○ Longer G1 phase ○ Shorter S phase, ○ More controlled and slower cell cycle This slower rate of proliferation helps maintain tissue homeostasis and function. Compare and contrast programming and reprogramming in terms of cell cycle regulation/regulators and length of cell cycle stages Programming vs. Reprogramming Programming: Refers to the process by which a cell differentiates into a specific cell type from a pluripotent state. Regulation: This involves changes in gene expression regulated by transcription factors that promote differentiation. Cell Cycle Length: Differentiated cells usually have a longer G1 phase and a regulated cell cycle compared to pluripotent cells. Reprogramming: Involves converting a differentiated cell back to a pluripotent state, as seen in induced pluripotent stem cells (iPSCs). Cell Cycle Regulation: This process often involves introducing transcription factors that reverse the differentiated state and restore pluripotency. Cell Cycle Length: During reprogramming, cells may exhibit an intermediate cell cycle profile, with changes in the duration of G1 and other phases, reflecting their transition state. Terms: Growth: the increase in physical size & cell number via division Proliferation: the active rates of division of cells M Phase: nuclear and cell division Interphase: Cell growth Cyclins: Regulatory proteins that control the progression of the cell cycle by activating cyclin-dependent kinases (CDKs). Cyclin D: Associated with the G1 phase and is crucial for progressing through the restriction point. Cyclin E: Works with CDK2 to transition from G1 to S phase. Retinoblastoma Protein (Rb): Regulates the restriction point by binding to and inhibiting E2F transcription factors, which are necessary for DNA synthesis. E2F Transcription Factors: Activated when Rb is phosphorylated, leading to the initiation of genes required for DNA replication. p53 and p21: Tumor suppressors that can induce cell cycle arrest if DNA damage is detected, ensuring that damaged cells do not progress to S phase. Totipotent: Refers to a cell's ability to differentiate into all possible cell types, including both embryonic and extraembryonic tissues. The zygote and the early blastomeres (up to the 8-cell stage) in mammals are examples of totipotent cells. Pluripotent: Refers to a cell's ability to differentiate into almost all cell types, except for extraembryonic tissues. Embryonic stem cells (ESCs) are a classic example of pluripotent cells, as they can become any cell type in the body but not the placenta. Embryonic Stem Cell (ESC): A type of pluripotent stem cell derived from the inner cell mass of a blastocyst. ESCs have the ability to self-renew indefinitely and differentiate into various cell types. Determination: The process by which a cell's developmental fate becomes more specific and committed to a particular lineage or cell type, often irreversibly. This is a step before differentiation. Specialization: The process by which a cell acquires distinct structural and functional characteristics specific to its role or cell type. Differentiation: The process through which a cell changes from a less specialized state to a more specialized state, acquiring specific functions and properties. Terminal differentiation: contributes to cell behaviors including motility and proliferation Morphogenesis: The process by which cells and tissues develop their shape and form during development. It involves a series of coordinated events that result in the spatial organization of tissues and organs. Pluripotency: Stem Cells that Maintain state capable of generation of all 3 embryonic germ layers Transcription Factors: Can be used to induce a pluripotent state (reprogramming) Dysregulated activation of separase could lead to premature separation of sister chromatids, which would disrupt proper chromosome segregation, but it wouldn't necessarily stop mitosis; it would cause errors in mitosis. Constitutive binding of APC and CDC20 would lead to continuous activation of the APC/C, potentially causing premature degradation of cyclins and securin, leading to issues with proper cell cycle progression, but not necessarily a complete halt in mitosis. Dysregulated inactivation of securin would prevent the proper activation of separase, leading to a failure to separate sister chromatids, which could delay or prevent mitosis from completing, but it is not as direct a block as the constitutive activation of MAD2. Two divisions of the cell cycle: - Interphase and Metaphase Chromosomes are only visible in which stage: - M phase Differentiated cells frequently do not have the same _______ _________ as their naïve or stem cell counterparts: - proliferative potential Differentiation is caused by and results in: - different patterns of gene expression Differentiated cells may also exhibit _______ or ________ responsiveness to growth signaling: - reduced or altered Factors affecting determination, differentiation, maintenance and modulation of the differentiated state of a cell during embryogenesis include what 4 things: - positional factors, hormones and paracrine factors, and external influences such as teratogens. List the following in order from earliest embryo development -> later embryo development: Pluripotent, Totipotent, Differentiated: - Totipotent -> Pluripotent -> Differentiated During which stage(s) would you observe a change in chromosome content? (LO1) - After S-phase but also after anaphase, true change in total content requires either replication or change in chromosome number - An area where Mitosis and meiosis differ What would you expect to observe for a cell where securin is irreversibly bound to separase? (LO2 and LO3) - Separase breaks down cohesion when it is broke free from securin - If irreversibly bound: - Cohesion wouldn't break down - Chromosomes don't separate - Stuck in metaphase - Anaphase needs unattached kinetochores Linking an error to the stage of mitosis: What sort of errors would cause a cell to stall in Prophase? (LO3) - Anything that disrupts microtubule dynamics - Anything preventing spindle formation, or nuclear envelope breakdown At which stage would a cell stall if there was an error in microtubule dynamics? - Generally, in prophase - if it specifies astral microtubules - Cytokinesis and formation of contractile ring will be impaired - We are stuck in telophase Linking Cytokinesis to Morphogenesis: How is polarity in a cell or developing embryo generated? (LO4) - Asymmetrical cell divisions and cytoskeleton activity - Cytoskeleton controls where cytokinesis takes place