BIO132 Lecture 6 Revision - Developmental Biology PDF

Dr. Ahmed Deghidy PhD Molecular Biology Alex U, Alexandria, Egypt Field of Basic Sciences ‫الدولية‬ ‫جامعة العلمين‬ 1  “BIO132” Lecture 6 “Revision” Dr. Ahmed Deghidy PhD Molecular Biology Alex U, Alexandr...

Dr. Ahmed Deghidy PhD Molecular Biology Alex U, Alexandria, Egypt Field of Basic Sciences ‫الدولية‬ ‫جامعة العلمين‬ 1  “BIO132” Lecture 6 “Revision” Dr. Ahmed Deghidy PhD Molecular Biology Alex U, Alexandria, Egypt An Example: A Frog’s Life  The Cycle of Life The stages of development between fertilization and hatching (or birth) are collectively called embryogenesis. 1. Fertilization involves the fusion of the mature sex cells “sperm and egg” “gametes”.  2. Cleavage a series of extremely rapid mitotic divisions that immediately follow fertilization. Zygote cytoplasm is divided into numerous smaller cells called blastomeres. By the end of cleavage, the blastomeres have usually formed a sphere, known as a blastula.  3. Gastrulation Blastomeres undergo dramatic movements and change their positions relative to one another, and the embryo is said to be in the gastrula stage. As a result of gastrulation, the embryo contains three germ layers (endoderm, ectoderm, and mesoderm).  4. Organogenesis Cells interact with one another and rearrange themselves to produce tissues and organs.  5. Metamorphosis Sexually immature organism needs to undergo metamorphosis to become a sexually mature adult.  6. Gametogenesis The gametes and their precursor cells are called germ cells (which contribute to the formation of a new generation). The germ cells migrate to the gonads, where they differentiate into gametes “gametogenesis”. gametogenesis is usually not completed until the organism has become physically mature.  7. Senescence Senescence is a process by which a cell ages and permanently stops dividing but does not die  Comparative Embryology some animals are born by some animals are born some animals are born by live birth (viviparity, as in from eggs (oviparity, as producing an egg that hatches placental mammals) in birds and frogs) inside the body (ovoviviparity, as in sharks)  Structure of the egg Egg has two poles: 1- Vegetal pole “the yolk-rich pole” 2- Animal pole “Where the zygote nucleus is frequently displaced , and the yolk concentration is relatively low” Types of Eggs Types of Eggs  Types of Cleavage 1- Holoblastic cleavage: In which the entire egg is divided into successively smaller cells, as in frogs and mammals 2- Meroblastic (incomplete) cleavage: In which only part of the egg is divided to become the embryo while the other portion “the yolk” serves as nutrition for the embryo, as in chicks. Types of Holoblastic cleavage Types of Meroblastic (incomplete) cleavage  Gastrulation: “The most important time in your life” Gastrulation usually proceeds by some combination of several types of movements.  Cell Differentiation The generation of specialized cell types is called differentiation a process during which a cell ceases to divide and develops specialized structural elements and distinct functional properties.  Commitment The process of commitment can be divided into two stages: 1- The first stage is specification 2- The second stage is determination The fate of a cell or tissue is said to be specified when it is capable of differentiating by itself  At the stage of specification, cell commitment is still labile (capable of being altered). If a specified cell is transplanted to a population of differently specified cells, the fate of the transplant will be altered by its interactions with its new neighbors A cell or tissue is said to be determined when it can differentiate autonomously even when placed into another region of the embryo or a cluster of differently specified cells in a petri dish During embryogenesis an undifferentiated cell matures through specific stages that commit it to a specific fate: 1- First Specification 2- Second Determination 3- Finally Differentiation During specification, there are three major strategies that embryos can exhibit: 1- Autonomous specification 2- Conditional specification 3- Syncytial specification  1- Autonomous Specification In autonomous specification, the cell “knows” very early what it is to become without interacting with other cells.  2- Conditional Specification What a cell becomes depends on its If cells are removed from the embryo, the position in the embryo. remaining cells can regulate and Its fate is determined by interactions with compensate for the missing part neighboring cells.  3- Syncytial Specification A cytoplasm that contains many nuclei is called a syncytium, and the specification of presumptive cells within such a syncytium Syncytial Specification is called syncytial specification. EX: fruit fly  Sox2 and Oct4 (which activated Nanog and other transcription factors that established pluripotency and blocked differentiation). c-Myc (which opened up chromatin and made the genes accessible to Sox2, Oct4, and Nanog). Klf4 (which prevents cell death. Applications of Induced Pluripotent Stem Cells