Fertilization
Fertilization
Opening title and credits. American Institute of Biological Sciences (AIBS), "Fertilization," Taught by Dr. Donald H. Bucklin from the University of Wisconsin.
Fertilization
Dr. Donald H. Bucklin standing next to photograph of egg surrounded by sperm, discussing the challenges sperm must go through in order to begin process of fertilization. Dr. Bucklin offers examples of ways different species go about fertilization. Male and female sea urchins releasing their sex cells in seawater, the sperm finding way to the egg. Illustration of male and female frogs mating. Sperm of a rat swimming, finding its way into an egg.
Fertilization
Dr. Donald H. Bucklin standing next to photograph of egg surrounded by sperm, discussing common factors in the processes of fertilization. Dr. Bucklin talks about external fertilization in phases, using props to illustrate. The first phase involves the release of the male and female sex cells.
Fertilization
Dr. Donald H. Bucklin, using props, talks about male sex cells (sperm) finding female sex cells (egg) in the next phase, called approach. Once the sperm reaches the egg, the next step is called penetration, where the sperm must enter the egg. The overall goal is for the head of the sperm to fuse with the nucleus of the egg, creating a composite nucleus in the phase called fusion.
Fertilization
Dr. Donald H. Bucklin says that as a result of penetration, the egg is induced to begin development through cell division, which is known as "activation." Male and female sea urchins releasing their sex cells. Microscopic view of egg and sperm cells. Dr. Bucklin notes that it is important for the sperm and eggs to be released at near the same time since both have very short lifespans outside of the body.
Fertilization
Illustration of a male and female frog. Dr. Donald H. Bucklin says the sexual embrace between the two frogs ensures that the release of the sperm and eggs occurs almost simultaneously. Female sea urchin releasing eggs. Dr. Bucklin notes that male and female sea urchin must be close to one another and the release of sex cells coincides with the release of a chemical substance which signals the partner to release their sex cells. Male sea urchin releasing sperm. The next problem is having the sperm find and approach the egg.
Fertilization
Dr. Donald H. Bucklin entertains the idea of the egg having some kind of chemical that attracts sperm to it. Dr. Bucklin notes that Lord Rothschild recently published findings that may show evidence of this possibility.
Fertilization
Dr. Donald H. Bucklin shows an enlarged diagram from Lord Rothschild’s paper which depicts sperm movement over a period of several minutes under microscopic observation. The movements are at random.
Fertilization
Dr. Donald H. Bucklin continues to look at diagram from Lord Rothschild’s paper depicting sperm movement over a period of several minutes under microscopic observation. Dr. Bucklin notes the glass tube placed into the solution containing sperm. Various chemical substances are contained within the glass tube. Dr. Bucklin shows another diagram showing sperm movement after the glass tube had been placed into the solution and the chemicals have been diffused-- the sperm seems to move in one direction, toward the glass tube. Biologists call this action Chemotaxis; movement under the influence of chemical substances.
Fertilization
Dr. Donald H. Bucklin asks: “Does Chemotaxis operate in eggs in nature?” There has been no conclusive study in nature to confirm. It appears sperm is released in close proximity to an egg, but the sperm swim at random in many directions. Nature seems to rely on large numbers of sperm so that some by accident may reach the egg.
Fertilization
Dr. Donald H. Bucklin says a chemical substance is involved during egg penetration by sperm. The chemical substance, fertilizin, aids in the penetration.
Fertilization
Dr. Donald H. Bucklin re-constructs part of the experiment originally conducted by American embryologist Frank Lilly which discovered fertilizin. Sea urchin eggs are placed in a beaker of seawater and allowed to stand. The sea water is filtered into a flask, which contains a small amount of fertilizin extract, or egg water.
Fertilization
Dr. Donald H. Bucklin, continuing fertilizin discovery experiment, places the fertilizin extract, or egg water, from flask into small dish. Dr. Bucklin takes sperm from a male sea urchin in a small dish and places it into the dish with egg water, mixes the two together.
Fertilization
Image of the the small dish with sea urchin sperm and egg water (fertilizin extract) mixed together. Successive images show the effects of fertilizin on sperm; sea urchin sperm clumping together in small, then large masses until finally there is only one clump of sperm in the center of the dish. Dr. Donald H. Bucklin states the action of fertilizin on sperm causes them to stick to each other.
Fertilization
Dr. Donald H. Bucklin asks if the Frank Lilly experiment, which discovered the chemical fertilizin, says anything about the penetration of sperm into the egg. Using props, Dr. Bucklin shows that sperm can stick to each other, but the question of whether sperm can stick to the egg is not really answered.
Fertilization
Dr. Donald H. Bucklin continues on the topic of possible fertilizin properties. What is known during the process of penetration is that as the sperm comes near the egg, a small rod comes out of the head of the sperm and attaches itself to the egg cell membrane, holding the egg in place. From the egg, a cone of cytoplasm travels up the rod and pulls the sperm into the egg. Fertilizin may have part to play in this process, but the exact part is yet unknown.
Fertilization
Dr. Donald H. Bucklin notes that once sperm penetrates the egg, the head of the sperm, its nucleus, merges with the egg nucleus. Fertilized egg in the process of activation. As the merged nucleus enlarges and moves toward the middle of the egg, the middle portion of the sperm transforms into the aster. Rays of the aster move out and begin to form the spindle. Once the spindle is formed, cell division begins.
Fertilization
Dr. Donald H. Bucklin says that while the steps follow from penetration of the sperm to fusion to activation, characteristics of activation can be seen the second the sperm touches the egg, starting with the changes to the egg cortex, or outer surface of the cytoplasm.
Fertilization
Dr. Donald H. Bucklin mentions that while the outer surface of the cytoplasm of the egg breaks down, another change within the egg occurs preventing other sperm from entering. What that change entails exactly is unknown.
Fertilization
Discussing further the subject of what prevents more than one sperm from entering the egg, Dr. Donald H. Bucklin mentions a defunct theory of the fertilization membrane of the egg rising to the surface and preventing other sperm from entering. Microscopic view of eggs with fertilization membrane shown. Dr. Bucklin: what is the mechanism of activation?
Fertilization
Dr. Donald H. Bucklin says that to find what triggers an egg’s activation, the egg must be activated without use of actual sperm. That way, it can be understood what the sperm does to make the egg develop. Dr. Bucklin notes that some eggs normally develop without entry of sperm, particularly some insects, rotifers, and the turkey. Praying mantis on a leaf stem. Microscopic view of rotifers. Turkey pecking ground. The ability for the egg to develop without sperm is known as Parthenogenesis.
Fertilization
Dr. Donald H. Bucklin notes the first experiments on artificial Parthenogenesis were done by Russian biologist A. Tichomiroff. Silkworm eggs being placed in a dish of concentrated sulfuric acid and mixed. Dr. Bucklin says the process did not kill the eggs but stimulated them to begin cell division, thus creating “fatherless silkworms." Dr. Bucklin says there are other ways to trigger artificial Parthenogenesis as explored by Jacques Loeb, American biologist. Illustration of Jacques Loeb.
Fertilization
Adult Caucasian male scientist adding butyric acid to dish of sea water and sea urchin eggs, mixing it. Dr. Donald H. Bucklin says this mixture slightly damaged the surface of the sea urchin eggs and began the process of development. Dr. Bucklin mentions a third method of artificial Parthenogenesis conducted by E. Bataillon, a French embryologist. Adult Caucasian hands puncturing frog eggs with a platinum needle dipped in frog blood. The result caused cleavage and, in a few cases, the eggs went on to produce fatherless frogs. Dr. Bucklin says this experiment has been recently successful in mammal experiments, specifically with rabbits.
Fertilization
Still photo of Dr. Gregory Pincus. Dr. Donald H. Bucklin explains the Parthenogenesis experiment Dr. Pincus conducted on rabbit eggs.
Fertilization
Dr. Donald H. Bucklin has each of the animals of the successful Parthenogenesis experiments on table in front of him: silkworms, sea urchin, frog, and rabbit. Dr. Bucklin notes that while the experiments were successful, they do not answer what exactly triggers activation in an egg, and do not explain what the sperm does to activate an egg because the means to imitate the activation can be done several ways: through strong chemical treatments, puncture, and chilling of the egg. Furthermore, more than one kind of treatment can work on the same type of egg.
Fertilization
Dr. Donald H. Bucklin says the only conclusive statement is that the egg is specialized for development, like a muscle cell is specialized to react to almost any kind of stimulation by contracting; Dr. Bucklin holds a frog, pinches its feet for muscle test. The same goes for the nerve cell, which reacts to mechanical, temperature, or electrical stimulation by conducting an impulse; electrical impulse test with frog muscle. Thus, the egg was built in the ovary with the property to being able to develop into a complete organism.
Fertilization
End credits.