Fertilization and Development

Question 1

Why Study development

Answer 1

• Understand and treat congenital abnormalities
• Discover what drugs are safe during pregnancy by testing them on other animals
• Understand the working of the mature body in a new light

Question 2

Development

Answer 2

• Go from 1 cell→ multicellular body
• Develop a body plan
• Involves: signaling, mitosis, differentiation, apoptosis, migration—all coordinated among the cells

Question 3

Differentiation

Answer 3

• As the cells divide, different transcriptional programs are turned on via signals from the environment
o Whatever’s on the left side will be in one daughter cell and whatever’s on the right side will be in another daughter cell
o Draw OUT DIFFERENTIATION
o Each division on the left side is asymmetric: produces one cell that retains its undifferentiated capacity as a stem cell
• Can form into whatever cell
o Each division on the right side is asymmetric: the other cell from each mitotic division acquires new traits through the transcription of genes
• Cannot form into whatever cell
Phases of Division

Question 4

Phases of division

Answer 4

Common to all organisms

fertilization, cleavage, gastrulation, neurulation, organogenesis

unique to a few: metamorphosis

Question 5

fertilization

Answer 5

• Gametes meet, generating a 1 celled, diploid organism called a zygote

Question 6

cleavage

Answer 6

• Cell division

Question 7

gastrulation

Answer 7

• First migration of cells to form the gut

Question 8

organogenesis

Answer 8

• Development of the organs

Question 9

metamorphosis

Answer 9

• Transition from larval stage to adult

Question 10

steps of fertilization

Answer 10

acrosomal reaction, cortical reaction

Question 11

acrosomal reaction

Answer 11

• Enzymes stored in the sperm acrosome digest a hole in the jelly coat of the egg
• Beneath the jelly coat, the sperm binding proteins bind sperm, trigger fusion of plasma membranes
• Sperm releases its nucleus into the egg

Question 12

cortical reaction

Answer 12

• Sperm binding to receptor triggers intracellular signaling events that cause release of Ca2+ from ER
• Ca2+ causes vesicles within the egg to be released
• Enzymes within
 Pull zona pellucida away from egg, hardening to protective “fertilization envelope”
 Cleave off sperm receptors (including any attached sperm)

Question 13

roles of Ca2+

Answer 13

• Triggers exocytosis of cortical vesicles, hardening of the zona
 Slow block to polyspermy
• Triggers egg activation
 Huge increases in rate of cellular respiration and protein syntheisis
 DNA synthesis begins

Question 14

cleavage

Answer 14

• Cell division without cell growth
• Resulting ball of cells stays roughly the same size, but increasing cell number
• Cells alternate between M and S phase, no G1 or G2
• Resulting ball of cells =blastula (each cells is a blastomere)
• Ball forms a central cavity called a blastocoel, fills with water

Question 15

yolks of different species

Answer 15

• Some egg laying organisms have large yolk sacs, so cell division is pushed toward one side (animal pole), yolk sac side is vegetal pole
• Mammals, and some others have a less pronounced yolk sac and cell division is more well distributed

Question 16

what is a yolk

Answer 16

• Food/nutrient sac

Question 17

cleavage in mammals

Answer 17

• Mammal embryos go through compaction, where they condense the ball of cells
• Then expanf the blastocoel space
• The embryo in this stageis called a morula
• Blastula is then called a blastocyst
• First differentiation event creates inner cell mass and trophoblat layer

Question 18

cessation of cleavage

Answer 18

• Cleavage appears to stop when the ratio of nucleus to cytoplasm in each blastomere is right
• Fertilized egg: very small nuc-cytoplasm ratio
• Each cleavage decreases size of cytoplasm

Question 19

cleavage in mammals

Answer 19

• Cleavage occurs in the oviduct (fallopian tube) as the egg descends from the ovary to the uterus

Question 20

implantation in mammals

Answer 20

• Implantation occurs when the trophoblast adheres to the wall of the uterus
• Uterine wall envelopes the mebryoprocess o
• Process of implantation takes about 1 week
• Trophoblast begins to proliferate and invade –becomes the placenta

Question 21

ovary

Answer 21

• The human ovary is both an endocrine gland and a reproductive organ
• Two functions are intricately tied
• Egg develops within a follicle
• Follicle produces hormones

Question 22

implantation and differentiation

Answer 22

• Implantation and invasion of the uterine wall by the trophoblast continues
• Further differentiation events occur in the inner cell mass
• 2 cell types: epiblast and hypoblast= bilaminar disc
• both begin to proliferate and migrate

Question 23

formation of “germ layers’

Answer 23

• Germ layers are the 3 precurosors to tissues that form in the embryo
• From these, all the tissues of the body form
• Endoderm
• Mesoderm
• Ectoderm
• All 3 are derived from the epiblast
• Hypoblast goes on to become “extra-embryonic” tissue

Question 24

gastrulation

Answer 24

• Process of cell migration and dramatic reorganization
• Paves the way for tissue differentiation
• After gastrulation 3 cell layers (germ layers)
o Endoderm (inner most) becomes the lining of organs & lining of CV system
o Mesoderm(middle) becomes skeleton, muscle, CV system, bottom of skin
o Ectoderm (outermost) becomes top layer of skin, nervous system, and germ cels

Question 25

notocord formation

Answer 25

• In the mesoderm, the notochord begins to form

Question 26

organogenesis

Answer 26

• Starts with neurulation—formation of the nervous system ((chordates))
• Doral (posterioir) mesoderm cells pinch off to become a rod called notochord (becomes the vertebral discs)
• Then ectoderm cells above this site change shape and curve inward (neural plate)
• Neural plate invaginated and pinches off, becoming neural tube

Question 27

two sets of cells develop around the neural tube

Answer 27

neural crest cells and somites

Question 28

neural crest cells

Answer 28

develop from neural tube (ectoderm) migrate around the body becoming nerves

Question 29

somites

Answer 29

develop from notochord (mesoderm) become vertebrae) (humans) also contribute to body segmentation in other vertebrates

• In some organisms somites contribute to segmented body plans
• In other organisms somites contribute to the formation of repetitive structures

Question 30

spinal bifida

Answer 30

• Error in neural tube closure

* Most common debilitating birth defect in US

Question 31

organogenesis pII

Answer 31

• The embryo folds in on its self during this process, to make a central cavity the length of the embryo—this becomes the gut
• The embryo stays connected to the yolk sac through a duct of the gut, this later becomes the umbilical cord (and after birth, the belly button)

Question 32

important factors in organogenesis

Answer 32

• Cytoskeleton
o Actin and microtubules make these programmed cell migrations possible
o Cells express adhesion molecules that help them adhere tot the ECM
o ECM plays an active role in guiding them in the riht direction
• Apoptosis
o Cells die in order to create a tissue pattern (tadpole tail, human hands)
o Cells compete for survival (only neurons with the most connections live)

Question 33

how do cells know what to become

Answer 33

• Long before the cells differentiatie and begin to look different, their fate is decided
• Factors within the cell itself (autonomous specification)
• Factors from outside the cell, usually signaling (uconditional specification)
• Combination of factors creates a unique internal/external ienvironment in which each cell may make unique changes in terms of gene expression

Question 34

determination

Answer 34

cells are committed to a fate

Question 35

differentiation

Answer 35

cells go through the genetic and morphological changes to become specialized

Question 36

the theory of fate mapping

Answer 36

undifferentiated cells in the blastula all appear the same However cells occupying a particular location ALWAYS deveop into a subset of specialized cells in the adult

Question 37

morphogens

Answer 37

• Cytoplasmic factors that convey positional information
• Are often autonomous regulators, but can be sectred, but can be secreted to work in a conditional manner
• Its not just presence/absence of morphogens but concentration

Question 38

cell fate and location

Answer 38

• Cells distinguish direction by stationary cilia, act like anyennas
• From this info, cells candecide how to migrate, etc
• Determines R and L patterns

Question 39

kartagener’s syndrome

Answer 39

• Defect in stationary cilia lead to incorrect placement of organs, without being able to detect the flow across the cell surface, cilia can’t correctly identify location

Question 40

birth defects

Answer 40

• By understanding the precise order and timing of events, we can better understand at what critical points in development things go wrong
• i.e. spinal bifida occurs around d28 of human gestation (lack of adequate folic acid)
• i.e. cleft palate: fusion of the structures that will form the upper jaw 5-7 weeks gestation (maternal ingestion of certain compounds)