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Lecture

Notes taken during lecture


Department
Biology
Course Code
BIO120H1
Professor
Jean Jiang Nash

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LECTURE April4th, 2011
DEVELOPMENT OF MULTICELLULAR ORGANISMS
Morphogenesis creation of 3d form in embryo
How cells differentiate?
1 cell embryo has everything it needs to
1.Morphogenesis
2.Cell differentiation
All based on transcriptional changes in cell encoded in genes
Cell proliferation = mitosis, cytokinesis, cell division
Cell specialization change in transcriptome, allowing cell to take on certain shape,
function,
Cell interaction cell signalling, cell to cell contact, adherens junctions, cell to matrix
contact, etc.
Cell migration movement early embryo very simple, to get more complicated, cells need
to get together
Whether to proliferate or not, which cells to interact with, where should migrate
THESE DECISIONS SAME AS CANCER CELLS MADE only inappropriately
It is important to know how model organisms develop, not just humans
Anything that is the same in multiple organisms = identified a core
developmental mechanism
Limit in how the model will help
But core mechanisms
Body divides self into parts each compartment develops independently of other
Development can be considered subdivision of subdivision of subdivision
Development doesnt only occur in embryo same processes occurring all the time
For instance, skin development
oConstantly sloughing off old layer of skin developing from stem cell
stage into mature skin cells
oSkin stem cells either divide into more stem cells or differentiate into skin
cells
oDivision is across stem cell division
oPink ones come from division of stem cells upwards pink at the top
oProduce lots of keratin, start to die, sloughed off
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oSo the entire system is always in flux, except for stem cell layer attached
to basal lamina connected to connective tissue of dermis
Dead cells continuously sloughed off and replaced by basal stem cells
Gut epithelia 2nd example of development after embryogenesis
Polyps in colon developed from misdevelopment
This are multicellular villi, at the top of which are cells sloughing off of top of
villus
oContinuously sloughing off
Harsh env , mutagenic env so better to slough off periodically
All sloughed off cells come down from the dent in the outer layer of gut lining,
called the crypt
oStem cells at the bottom produce upwards divide and divide in yellow
As cells move further and further away, stop dividing to
differentiate
Form permanent epithelial cell Gzero
Live for a while, make up to top of villus, slough off and die
This is lifecycle
Mammory gland development
Stop at embryonic stage
But during pregnancy hormonal instructions cause cells to proliferate called
alveoli
oAlveoli produce milk fat droplets secreted into
Only develop during pregnancy
Other two are tissue maintenance vs. adult/late development for the mammory gland
Is embryogenesis
Idea of how cells tell how they are different v. common mechanisms
Mouse embryo
Begins with the formation of a ball of cells-the blastocyst
Single celled embryo
See dents of two nuclei called pronuclei nucleus of egg and sperm, not yet
fused
Cells divide over and over again into loose ball of cells
Btw picture 4 and 5, cells start to express cadherin transcription turned on
oThus protein made, goes to cell surface, cells stick together, form
epithelium
Mouse embryo the pink fifteen circle inner cell mass is where embryo
develops
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