Calcium Waves through Medaka Fish Eggs during Fertilization
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| License | No Open Access License: German copyright law applies. This film may be used for your own use but it may not be distributed via the internet or passed on to external parties. | |
| Identifiers | 10.3203/IWF/C-1736eng (DOI) | |
| IWF Signature | C 1736 | |
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| IWF Technical Data | Film, 16 mm, LT, 68 m ; F, 6 1/2 min |
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Transcript: English(auto-generated)
00:23
Most unfertilized eggs are in a state of developmental arrest. One important function of fertilization is to activate the egg, resulting in the continuation of development. The medaka egg is a 1200 micrometers diameter cell.
00:45
Its 40 micrometers thick cytoplasm contains big vesicles and, as seen here, oil droplets. As the diagram shows, an egg has a large central yolk compartment surrounded by a thinner layer of cytoplasm and protected by a tough membrane, the corion.
01:08
The corion possesses an opening, the micropyle, at the animal pole for fertilization. The experiments will show an explosive rise in free calcium during fertilization.
01:23
To prove this, equorin is injected into the cytoplasm. Equorin binds free calcium and thereby emits one photon. The luminescence of this photoprotein then indicates the level and pattern of free calcium within the cytoplasm.
01:49
In the first experiment on an egg prepared in this way, the sperm enters from the left. The calcium effect triggered by this event is observed on a video screen by image intensification.
02:05
The calcium wave starts at the animal pole where the sperm entered and traverses the egg in about two minutes. The movement is shown here at about three times natural speed.
02:21
Each light spot of the original video tape indicates one photon of emitted light. The wave now slows down. It lingers at the vegetal pole where it finally dies out.
03:05
In the second experiment, the equorin-loaded egg is entered by a sperm from the viewer's direction. The luminescent reaction between equorin and free calcium extends over the egg as a concentric ring.
03:35
The reaction may seem to be confined to the egg's surface, but in fact it fills the whole of its cytoplasm, surrounding the yolk compartment,
03:44
which is seen as a dark central area. The reaction will end at the vegetal pole on the opposite side of the egg.
04:16
In the third experiment, the equorin-loaded egg is activated by a colloidal suspension of a calcium ionophore instead of sperm.
04:30
Four separate calcium waves are starting, each from a different point. They never spread through each other but fuse upon meeting.
04:42
The rings did not cross each other because the stored calcium needed for the reaction is exhausted.
05:10
A propagated calcium wave is believed to be the primary mechanism which activates eggs on the vertebrate line and thus triggers their further development.
05:24
In the medaka egg, this development begins with the migration of oil droplets to the vegetal pole.