Lecture Notes: Gametogenesis and Fertilization
Introduction
Key components from the lecture include details on upcoming exams and batches, an overview of developmental biology, and the main conceptual points of stem cells and their division.
Key Announcements
- New Batch Start Date: 9th July for CSIR NET Life Sciences, targeting December 20 exams
- GATE Classes: Ongoing for GATE 2025 in various subjects
- Registration Details: Course fees and availability
Developmental Biology
Basic Concepts
- Potency: Power to produce different types of differentiable cells
- Similar to students' ability to prepare for exams successfully
- Commitment: State when a cell's developmental fate becomes restricted
- Two stages: Specification & Determination
- Specification: Reversible stage where cells can revert back
- Determination: Irreversible stage where cells can't change fate
Types of Cell Specification
- Autonomous Specification: Determination set by internal factors like transcription factors from the egg's cytoplasm
- Conditional Specification: Determination by interaction with other cells, requiring positional context
- Syncytial Specification: Utilizes elements of both autonomous and conditional specification
Gametogenesis
Timing of Meiosis
- Females: Begins in embryo (pre-natal)
- Males: Begins at puberty (post-natal)
Process Overview
- Oogenesis: Formation of ovum
- Spermatogenesis: Formation of sperm
- Regulatory factors like STRA8 influenced by WNT4 and retinoic acids in ovaries, and FGF9 in testes
- GDNF from Sertoli cells keeps spermatogonia dividing
Fertilization
Steps of Fertilization in Sea Urchins
- Chemoattraction: Attraction of sperm to egg via chemical signals
- Acrosome Reaction: Fusion of sperm's acrosome with its cell membrane, releasing enzymes
- Binding: Sperm binds to the egg
- Passage of Sperm: Sperm passes through external egg layers
- Fusion: Fusion of sperm and egg cell membranes
Key Mechanisms
- Chemoattraction: Involvement of species-specific molecules
- Examples: Resact (for Arabacia punctulata) and Speract (for Strongylocentrotus purpuratus)
- Acrosome Reaction: Initiated by species-specific sulfated polysaccharides
- Activation of calcium channels, sodium-hydrogen exchangers, and phospholipase C
- Formation of acrosomal process by polymerization of actin
Important Points
- Specificity mechanisms to ensure correct species fertilization
- Role of calcium ions in acrosome reaction and sperm activation
Stem Cells
Key Characteristics
- Self-renewal: Ability to divide and create identical copies
- Potency: Ability to differentiate into various cell types
- Stem Cell Division: Symmetrical and Asymmetrical
- Symmetrical: Produces either two stem cells or two committed cells
- Asymmetrical: Produces one stem cell and one committed cell
Potency Types
- Totipotent: Can form all cell types including extra-embryonic structures
- Pluripotent: Can form almost all cell types but not extra-embryonic structures
- Multipotent: Can form multiple cell types within a related family
- Unipotent: Can form only one cell type
Stem Cell Niche
- Provides regulatory environment using physical and chemical signaling
- Maintains a balance between stem cell renewal and differentiation
Yamanaka Factors
- Essential transcription factors required to induce pluripotency
- Key Factors: Sox2, Oct4, Nanog, c-Myc, and Klf4