Download Fertilisasi

Fertilisasi
Landak Laut
(Sea Urchin)
Landak Laut / Sea Urchin
Struktur Anatomi Landak Laut
Notice how the needle goes into the soft part between the teeth
and shell, on the opposite side from the syringe. This "squirts"
the potassium chloride onto the gonads causing them to
contract and expel the gametes.
HOW TO SPAWN AN URCHIN
A 2cc syringe filled with 0.5M potassium chloride is inserted into the sea urchin
between the teeth and the hard outer shell. A small amount of potassium chloride is
injected into the urchin on each side (amount varies with size of urchin,
0.1cc/inch/side). This induces the urchin to spawn IF it has any eggs or sperm left.
WARNING: ONLY TEACHERS should do this. Potassium chloride is potentially lethal
if used improperly.
A milliliter of 3.7% potassium chloride is
injected into each side of the sea urchin.
(Smaller amounts for smaller sea urchins.
A Lytichinus pictus would only need a
tenth of a milliliter per side.)
Smaller gauge, 25-30, needles work best.
Female S. purpuratus
Orange indicates a female in most species (can be redish in others).
Invert the sea urchin over a beaker of seawater and fill to the rim with
seawater by pouring seawater over the sea urchin. Let the eggs drop
to the bottom of the beaker.
Eggs should be used that class period unless you have used one of
the special techniques to preserve them longer.
HOW TO COLLECT EGGS
The injected female urchin is placed mouth side up over a beaker filled with
sea water. The eggs will then be shed into the sea water and settle down to
the bottom of the beaker. Store the eggs at the same temperature as would
be best for development in this urchin.
Males can be collected "dry" by sucking up the sperm from the
top of the sea urchin (white) with a pipette and collecting the
sperm into a small centrifuge tube or test tube. Sperm may be
stored at 4C in a refrigerator for up to a week.
HOW TO COLLECT SPERM
The injected male urchin is placed on a dry surface mouth side down.
The sperm are collected with a glass or plastic pipet and stored in a
test tube at 4C for later use.
NORMAL DEVELOPMENT
In normal development the sperm fertilizes the egg. The cortical reaction
occurs raising the fertilization membrane and cell divisions occur until the
blastula stage. When the embryo reaches the blastula stage the embryo
releases an enzyme that dissolves the fertilization membrane and the young
embryo swims free to continue development.
The red receptors on the sperm come into contact with the egg jelly, yellow. This induces
the acrosome reaction causing the acrosome in green to fuse with the plasma
membrane of the sperm. The actin in pink goes from a globular state to a filamentous
state pushing the front of the sperm outward exposing the binding receptors, blue. The
binding receptors can now bind with the egg
The cytoplasm of the sperm contains NOS (Nitric Oxide Synthase) which is
activated along with the acrosome reaction by contact with egg jelly [yellow] [NOS
turns green here when activated]. Activated NOS produces Nitric Oxide [light green
spray].
Upon fusion with the egg, NOS is released into the egg, whereby the NO produced
activates Calcium release [red spray]. Calcium activates NOS already present in
the egg, releasing more NO, which releases more Calcium, etc. Starting a wave of
calcium throughout the egg.
SPERM MOTILITY
The sperm moves by rotating its tail in a spiral motion through the
water. This induces waves of force backward propelling the sperm
forward. If the sperm hits a hard surface, like an egg, the spiral
motion will cause the entire sperm to rotate.
SPERM MOTILITY
The sperm moves by rotating its tail in a spiral motion through the water. This
induces waves of force backward propelling the sperm forward. If the sperm
hits a hard surface, like an egg, the spiral motion will cause the entire sperm
to rotate.
TOO MANY!
Too many and the embryos will be polyspermic and die.
TOO FEW!
Too few and the eggs will not be fertilized
JUST RIGHT!
With just the right number of sperm all of the eggs get
fertilized and development occurs normally.
FUSION
Note the surface proteins on the plasma membrane and the vesicle membrane. When
the vesicle fuses with the plasma membrane the proteins on the plasma membrane are
displaced and proteins inside the vesicle are now exposed to the outside of the cell. The
contents of the vesicle are expelled into the environment. In the case of the special
"cortical granules" of the sea urchin egg, this expelling of contents is what raises the
fertilization membrane, preventing further sperm entry.
NORMAL FERTILIZATION
The sperm enters and binds to the egg surface. This induces a calcium wave
that causes the cortical granules, white, to fuse with the plasma membrane,
releasing their contents and causing the fertilization membrane to rise. The
sperm is then pulled into the egg where it moves to the egg nucleus and
fuses. DNA synthesis occurs along with duplication of the centrosome,
black. Nuclear envelope breakdown and chromosome condensation leads
to the metaphase plate. Anaphase leads to telophase and cell division. The
process is repeated.
POLYSPERMY
If two or more sperm make it into the egg polyspermy occurs. In this case some
of the genetic material condensed into chromosome is attracted to the extra
sperm causing abnormal development and ultimately the death of the
embryo. Too many sperm and toxic conditions can lead to polyspermy.
NUCLEAR MIGRATION
This time-lapse video shows the female pronucleus moving to the
center of the embryo where it will fuse with the male pronucleus.
The numbers in the lower left corner are minutes after fertilization.
Species is Lytichinus pictus at about 18C.
Red arrow points to the nucleus.
From single cell to 4 cell
Pembelahan 4 sel - Morula
UNEQUAL DIVISION
In this animation we see how an unequal division of the centrosome can result in an
unequal cell division. Notice how the smaller mitotic apparatus gets "pushed" to the
edge of the dividing cell. The RED area at the bottom of the unequal cell appears to
really exist, "sticking" to the mitotic apparatus when it comes into contact.
Egg Fertilized
Early Cleavage
Blastula
Plutei Larvae
Sea Urchin Embryo 1-Cell to
Blastula
GASTRULATION IN SEA URCHINS
CROSS SECTIONAL VIEW: Yellow is ectoderm, orange is
endoderm, red is primary mesenchyme cells and skeleton, orange
"dots" are secondary mesenchyme cells. Process from "blastula" to
"pluteus" takes about 48 hours.
Note: Anus is formed before the mouth.
Development in the sea urchin from the one cell to the late prism stage.
Note the MICROMERES are highlighted in RED. The micromeres are
essential for gastrulation. At the prism stage the free swimming embryo
starts to feed. Remember, in deuterostomes, the anus forms first and then
the mouth.
1 CELL TO URCHIN
PLUTEUS TO URCHIN
The pluteus larva grows over the period of 4-6 weeks, till it is big enough and developed enough to
metamorphose. Metamorphosis itself takes place in only a few hours time. The "skeleton" of the pluteus becomes
the spines of the new sea urchin. The gut transforms into the test [shell] of the sea urchin.
Many thanks to Margaret and Greg for this contribution. If you use this animation, please give them credit.
Table 1. Approximate Timetable for Sea Urchin Development.
Event
Time Range
Average Time
Formation of fertilization 1/2-5 minutes
membrane
1 minute
First cleavage
1-3 hours
1 hour +
4 Cell and 8 Cell
stages
16 cell stage
2-7 hours
4 hours
6-13 hours
7 hours
Morula
8-24 hours
14 hours
Blastula
9-48 hours
24 hours
Gastrula
20-100 hours
32-40 hours
Plutues larva
50-200 hours
60-100 hours