CAS BI 105 Lecture Notes - Lecture 17: Neurulation, Organogenesis, Gastrulation
30 Apr 2018
School
Department
Course
Professor
Fertilization and Development
Why study development?
•To understand and treat congenital abnormalities
•Discover what drugs are safe during pregnancies by using animal testing
•To understand how the mature body works
Development
•Development is an exercise in multicellularity
•We are transitioning from 1 cell (that contains all of the genome) —> multicellular body in order to
develop a body plan
•Involves: signaling, mitosis, differentiation, apoptosis, migration, pluripotent - not differentiated)
•^this is all coordination by the cell
Differentiation
•As cells divide, different transcriptional programs are turned on by signals from the environment
•During differentiation, transcriptional programs are separated due to their location (what side of the
cell it on)
Asymmetric Cell Division
•Each division is asymmetric
•Produces one cell that retains its undifferentiated capacity as a stem cell
•The other cell from each mitotic division acquires new traits through the transcription of genes
•Development is highly conserved
•Similarity amongst organisms
•ex: skin to protect the out from the in
•Most embryos look similar to each other
Phases of Development
•Common to all organisms:
•Fertilization
•Cleavage
•Gastrulation
•Neurulation
•Organogenesis
•Unique to some:
•Metamorphosis
•ex: amphibian, frog (not in humans)
Description of Phases
•Fertilization
•Gametes meet
•This generates a single celled, diploid organism called a zygote (fertilized egg)
•Impossible to complete with one gamete
•Cleavage
•Do not need a lot of time —> because the cytoplasm is so large
•Cell division through multiple rounds of mitosis
•Gastrulation
•The first migration of cells to form the gut/digestive tract (cells are moving instead of dividing)
•Neurulation
•Differentiation & Migration of cells to form the beginnings of the nervous system
•Organogenesis
•Development of the organs
find more resources at oneclass.com
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•Metamorphosis
•Transition from larval stage to an adult
STEPS OF EACH:
1. Fertilization
•Acrosomal Reaction
•Enzymes stored in the sperm acrosome digest a hole in the jelly coat of th egg
•Beneath the jelly coat, the sperm binding proteins bind sperm —> triggering a fusion of plasma
membranes
•Sperm then releases its nucleus into the egg
•Fusion
•Fusion of the membranes trigger a depolarization event
•Depolarization prevents other sperm from binding (fast block to polyspermy)
•Cortical Reaction
•Sperm binding to the sperm-binding receptor will trigger intracellular signaling events that cause
the release of Ca2+ from the endoplasmic reticulum
•Ca2+ causes vesicles within the egg to be released
•Enzymes within:
•pull the zona pellucida away from the egg, hardening to protective fertilization envelope
•Cleave off sperm receptors (including any attached sperm)
•The roles of Ca2+
•Triggers exocytosis of cortical vesicles, hardening the zone
•This is the block to polyspermy!
•Triggers an egg activation
•Huge increase in the rate of cellular respiration and protein synthesis
•DNA Synthesis begins
2. Cleavage
•Cell division without cell growth
•The resulting ball of cells stays roughly the same size but the cell number (amount of cells) increase
•Cells alternate between M and S phase, but there is no G1 or G2 phase
•Can take a variety of time, but usually a couple of days in humans
•Terms To Know:
•Blastula - resulting ball of cells
•Blastomere - each cell in the call of cells
•Blastocoel - the central cavity filled with water (formed by the ball of cells)
The Yolks of Different Species
•Some egg-laying organisms have large yolk sacs
•^this results in cell division being pushed towards one side )the animal pole) while the other side
containing the yolk sac side (the vegetal pole)
•Mammals and some others have a less-pronounced yolk sac, making cell divines more well
distributed
•Yolk - a food/nutrient sac
•^is used to describe a portion of an egg
•Egg White: layers of albumin for cushioning and antimicrobial protection
•Egg Yolk: the actual egg cell that is swollen with egg nutrients
Cleavage in Mammals
•Mammal embryos go through compaction, where they condense the ball of cells
•Then the blastocoel space is expanded
•The embryo in the stage is called a morula
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Why study development: to understand and treat congenital abnormalities, discover what drugs are safe during pregnancies by using animal testing, to understand how the mature body works. Differentiation: as cells divide, different transcriptional programs are turned on by signals from the environment, during differentiation, transcriptional programs are separated due to their location (what side of the cell it on) Phases of development: common to all organisms, fertilization, cleavage, gastrulation, neurulation, organogenesis, unique to some, metamorphosis, ex: amphibian, frog (not in humans) Cessation of cleavage: cleavage appears to stop when the radio of nucleus to cytoplasm in each blastomere s right, fertilized egg: very small nub-cytoplasm ratio, each cleavage decreases the size of the cytoplasm. Ovary: the human ovary is both an endocrine gland and a reproductive organ, the two function are intricately tied, the egg develops within a follicle, follicle produces hormones (estrogen & testosterone)
