Lecture 1 Notes.pdf

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Department
Biological Sciences
Course Code
BIOC19H3
Professor
Ian Brown

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Lecture 1 Notes: Principles of Development What is developmental biology? ▯ - the study of the developing animal from the fertilized egg right through to the adult stage ▯ - Study of the development of specific tissue (e.g. formation of blood cells) Can be studied at two levels: ▯ - Morphological level (how the tissue looks as it develops, change in gene expression) ▯ - Molecular level Course Central Theme ▯ - Regulation of gene expression underlies morphological changes seen in development ▯ - Example: the gene HMGA2 is a key gene regulating height in people. Although its exact ▯ mechanism remains unknown, it is thought to increase cell production. But, many genes work ▯ together to achieve a morphological trait, including height Historical Advances in Developmental Biology ▯ Phase 1: Descriptive Studies ▯ ▯ - Visual observations ▯ ▯ ▯ - Chicken development advantages: ▯ ▯ ▯ ▯ 1. Development occurs outside the female, externally ▯ ▯ ▯ ▯ 2. Chickens are laying eggs all the time, no problem obtaining eggs. If we ▯ ▯ ▯ ▯ crack the egg at different times, we can see different developmental stages ▯ ▯ ▯ ▯ 3. After the egg is laid and you cool it down, you can slow down the speed of ▯ ▯ ▯ ▯ development, a way to harvest the stages ▯ ▯ ▯ ▯ 4. It was realized that it shows some similarities to developmental stages in ▯ ▯ ▯ ▯ mammals ▯ ▯ ▯ - Detailed anatomical drawings made using the naked eye ▯ ▯ - Microscopic observations ▯ ▯ ▯ - Invention of the compound light microscope depend on: ▯ ▯ ▯ ▯ 1. Advances in glass making techniques (for lens development and ▯ ▯ ▯ ▯ improvement) ▯ ▯ ▯ ▯ 2. Proper specimen preparation ▯ ▯ ▯ - Tissue preparation for microscopy: ▯ ▯ ▯ ▯ 1. Fixation: ▯ ▯ ▯ ▯ ▯ - Preserves the tissue in its natural state ▯ ▯ ▯ ▯ ▯ - Prevents autolysis (tissue breaking down, rotting, contaminating) ▯ ▯ ▯ ▯ ▯ - Makes tissue hardy (in order to slice) ▯ ▯ ▯ ▯ ▯ - Method can be either physical (heat/cold) or chemical ▯ ▯ ▯ ▯ ▯ - A note of caution: fixation can cause artifacts: ▯ ▯ ▯ ▯ ▯ ▯ - Artifact is a structure not naturally present in the sample being ▯ ▯ ▯ ▯ ▯ ▯ observed that arises during tissue preparation ▯ ▯ ▯ ▯ 2. Embedding: ▯ ▯ ▯ ▯ ▯ - Provides additional structural rigidity to tissue ▯ ▯ ▯ ▯ ▯ - Embed the tissue in paraffin/wax ▯ ▯ ▯ ▯ 3. Sectioning: ▯ ▯ ▯ ▯ ▯ - Thin slices of tissue ▯ ▯ ▯ ▯ ▯ - Uses: Microtomes, vibratomes, cryostats ▯ ▯ ▯ ▯ ▯ - A chemical called xylene can then be used to dissolve the wax ▯ ▯ ▯ ▯ 4. Staining: ▯ ▯ ▯ ▯ ▯ - Chemical stains for staining different molecules, either general stain ▯ ▯ ▯ ▯ ▯ or a specific stain ▯ ▯ ▯ ▯ ▯ - A fluorescent tag can be used ▯ ▯ ▯ - Advances made with the light microscope: ▯ ▯ ▯ ▯ 1. All organisms are composed of cells ▯ ▯ ▯ ▯ 2. Number of cells increase with development through cell division ▯ ▯ ▯ ▯ 3. Structure of individual cells increases in complexity with development, the ▯ ▯ ▯ ▯ shape changes ▯ ▯ ▯ ▯ 4. Cells organize into tissues and organs ▯ ▯ ▯ - Advances made with electron microscopy: ▯ ▯ ▯ ▯ 1. Cells are composed of organelles ▯ ▯ ▯ ▯ 2. Complexity and number of organelles within a cell increases during ▯ ▯ ▯ ▯ development ▯ ▯ ▯ - Confocal microscope: ▯ ▯ ▯ ▯ - Optical sections through a specimen allowing for 3D structures ▯ ▯ ▯ ▯ - Allows for live imaging to look how living cells change in development ▯ ▯ Phase 2: Comparative Studies ▯ ▯ ▯ - Compare the embryological sequence in different species ▯ ▯ - Recapitulation Theory: ▯ ▯ ▯ - Ontogeny recapitulates phylogeny: ▯ ▯ ▯ ▯ 1. The development of an organism (ontogeny) demonstrates the evolutionary ▯ ▯ ▯ ▯ history of its species (phylogeny) ▯ ▯ ▯ ▯ 2. All embryos are similar early in development reflecting their common ▯ ▯ ▯ ▯ ancestry ▯ ▯ ▯ ▯ ▯ - Also known as biogenetic law ▯ ▯ ▯ ▯ ▯ - 1866 Ernst Haekel ▯ ▯ ▯ ▯ ▯ - Overemphasized similarities between embryos of related species ▯ ▯ ▯ ▯ ▯ - Theory is no longer accepted ▯ ▯ Phase 3: Experimental Embryological Developmental Studies ▯ ▯ ▯ - Modify normal development in order to study its underlying mechanisms ▯ ▯ - Early embryogenesis: ▯ ▯ ▯ - Embryogenesis is followed by organogenesis (formation of organs) ▯ ▯ - Three germ layers: ▯ ▯ ▯ 1. Ectoderm: gives rise to nervous system, epidermis of skin, hair, nails, sweat ▯ ▯ ▯ glands, teeth, lens of eye ▯ ▯ ▯ 2. Endoderm: gives rise to linings of stomach, intestines, pancreas, liver, lungs, ▯ ▯ ▯ urinary bladder ▯ ▯ ▯ 3. Mesoderm: muscle, blood, bone, connective tissue, dermis of skin ▯ ▯ - Vital staining: ▯ ▯ ▯ - Stain that is taken in by live cells ▯ ▯ ▯ - Non-toxic initially (often leads to eventual death of the cell) ▯ ▯ - Fate maps: ▯ ▯ ▯ - Fate map: diagram of an early embryo showing which tissues the cells in each ▯ ▯ ▯ region will give rise to ▯ ▯ ▯ - First done on frog eggs ▯ ▯ ▯ - How to construct a fate map: Stain cell(s) early wit a vital stain in development and ▯ ▯ ▯ later examine to determine what structure
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