01:119:116 Lecture Notes - Lecture 16: Sea Urchin, Metaphase, External Fertilization
29 Oct 2018
School
Department
Course
Professor
Development I (Ch 47.1)
I. Introduction
○ SEQ development
II. Fertilization
○ SEQ fertilization
○ CC fertilization in different animals
III. Cleavage
○ SEQ, IOV cleavage
○ CC cleavage patterns
I. Introduction
A. Development
- All of the changes that occur during the life of an individual
- During embryonic development and following birth/hatching
- Simple → complex / specialized
B. Model organisms
- Species chosen for research: easily studied
- Most amount of research on: sea urchin, frog, chick, nematode
C. Ongoing process
-
II. Fertilization
A. Intro
1. Sperm- flagella + motile
- Fuses w/ egg: larger, immotile
-----> zygote: fertilized egg, single cell
2. Consequences
a) Restores 2n
b) Determines sex
c) Activates egg
----> stimulates reactions for development
3. Egg
- Surrounded by plasma membrane (PM)
- One or more coverings
a) Aid in fertilization by sperm of same sp
b) Barrier to interspecific fertilization
4. Steps in fertilization
a) Sperm dissolves protective layers around egg to reach PM
b) Molecules on sperm surface that bind to receptors on egg surface
c) Surface of egg changes to prevent polyspermy
5. Sea Urchin
- Phylum Echinodermata
a) Readily available
b) Easy to work with
c) Lots of gametes
d) External fertilization
B. Sea Urchin
1. Egg coverings
- Internal to external
a) PM
b) Vitelline layer- thin
c) Jelly coat- thick glycoprotein layer
2. Gametes - released into water
- Jelly coat: chemicals into water
- Attract sperm → chemotaxis
3. Sperm contacts jelly coat + undergo acrosomal reaction
a) Acrosome
- Vesicle on head
- Hydrolytic enzyme
- Digest jelly coat
b) Acrosomal process
- Sperm structure- actin filaments
- Protrudes from sperm head + penetrates jelly coat
- Protein molecules at tip bind to specific receptors on PM
4. Recognition between sperm + egg triggers fusion of their PM’s
- Sperm nucleus enters egg
→ plasmogamy
- Once this nucleus is in, no more should enter
5. Fast block to polyspermy
- Triggered by fusion of PMs
a) Unfertilized egg polarized
- Cytoplasm negatively charged rel. to outside
b) Within seconds after sperm fuses + nucleus enters egg
→ ion channels in egg PM open
c) Sodium ions (Na+) enters egg
d) Egg depolarizes
- Very soon after sperm binds to egg
e) Prevents fusion w/ other sperm
f) Transient ( does not last very long)
- Lasts only for around a min
6. Slow block to polyspermy
- Cortical reaction
a) Binding of sperm to egg triggers signal transduction pathway
- Triggers release of Ca 2+ from ER to egg cytoplasm
- Increased levels of Ca2+ triggers cortical granules
b) Cortical granules
(1) Vesicles - lie in cortex
- Rim of cytoplasm just beneath egg PM
(2) Release enzymes
- Space between PM + vitelline layer
c) Cortical reaction
(1) Vitelline layer lifts away from egg + hardens
→ fertilization envelope prevents other sperm
(2) Enzymes clip off+ release external portions of receptor
proteins
- Any attached sperm
d) Requires around a min
e) Irreversible + permanent
Fig 47.3
Document Summary
All of the changes that occur during the life of an individual. Simple complex / specialized: model organisms. Most amount of research on: sea urchin, frog, chick, nematode: ongoing process. ----> zygote: fertilized egg, single cell: consequences, restores 2n, determines sex, activates egg. Phylum echinodermata: readily available, easy to work with, lots of gametes, external fertilization, sea urchin, egg coverings. Internal to external: pm, vitelline layer- thin, jelly coat- thick glycoprotein layer, gametes - released into water. Attract sperm chemotaxis: sperm contacts jelly coat + undergo acrosomal reaction, acrosome. Protrudes from sperm head + penetrates jelly coat. Protein molecules at tip bind to specific receptors on pm: recognition between sperm + egg triggers fusion of their pm"s. Once this nucleus is in, no more should enter: fast block to polyspermy. Triggered by fusion of pms: unfertilized egg polarized. Cytoplasm negatively charged rel. to outside: within seconds after sperm fuses + nucleus enters egg.
