About science; About development in animals

This is about science produced by the California Institute of Technology and originally broadcast by station KPCC in Pasadena California. The programs are made available to the station by national educational radio. This program is about development in animals with host Dr. Peter listen and his guest Dr. Albert Tyler professor of biology here now is Dr. listen that's the most persistent question of all time. The one the children first are their parents. Where did I come from. Why am I the way I am. What makes me work. How do I care that child on this. And as Wordsworth has said the child is father to the man. Man our good man child has always off there Christian. Where did I come from. How do animals develop well over all the centuries that that question has been asked. The answer still is Indian. But we are getting closer and we know that

it is a very complex reply. But the child in man that keeps on asking will not be satisfied until these mysteries are unraveled. There was a time when one could put all children by telling him that the stork brought him or put up simple people by telling them something about the mythology or the ways of God and man. But in our modern days man can never be put off by what he considers you know adequate information. And he probes and probes until he gets to the root of the matter. Where then do we come from and whom can we are asking about the very beginning of life about the development of the new individual. Who knows enough about the hidden processes of growth and development to give some clear answers. The first person to ask of course is the biologist. Since he deals with some of the most basic questions of life. We're fortunate today to have a distinguished

biologist with us Dr. Albert Tyler who will discuss the early development of living creatures creatures that might range all the way from purposes to people. Dr. Tyler a professor of biology at Cal Tech took his bachelor's and master's degree at Columbia University in New York and finished his doctoral degree at Cow Tech where he has researched for many years. In addition to research abroad in England Germany and Italy at Cal Tech Dr. Tyler's researches range from the study of the poison and healing monsters to the development of sea creatures and higher animals. Dr. Turner. What is the first thing that we should discuss. So I think maybe the history how long have people been asking themselves these questions and when have they started to arrive at an onset. Dr. Lipman as you mentioned. This is one of the first questions that the intelligent child is likely to ask his

parents and we can assume that these questions were asked by children and take Whitty. But the first recorded scientific investigations were probably those of our startle and other early Greek investigators. And there's been a rather continuous line of research from that time to the present. With increasingly great activity going on at present. And so as you say it probably breaks today. We have been looking at this question and I suppose thinking about this question has led to large areas of our knowledge in biology and hereditary. Yes. Our first analyses of heredity were derived from knowledge of the fact

that two cell sperm and egg united to form a new individual. Many other areas of biology have been promoted by talking about developmental processes. So what exactly we mean by development then docked time that ends this process by which the egg transforms itself into something else. That's correct. Essentially it is the process by which the fertilized egg transformed itself into the adult organism. The way the various tissues and organs of the body formed. So you're not really talking about how life actually starts but what happens once life has begun. And exactly that if one discusses the flight of life from one generation to another and we usually

consider this under the topic of reproduction I seen not develop into preproduction. Dr. Tang to what animals do you choose to study for your work. Mostly we work with lower animals with Marina moved largely to some extent with frogs with chickens with mice rats and occasionally with humans. Is there anything important about the animal you're trues. Yes we choose those animals which provide us with the largest numbers of eggs but we want large numbers and those which are most readily handled in the laboratory. One must remember that the most basic processes are those which are common to all animals and plants as well. So I see so that your animals show these same things what about

our time of the basic questions that you could ask any animal to provide you with. Well first of all are questions concerning the preparation of eggs and sperm how the egg attains its full size and configuration of the ovary how sperm are produced. And there are problems as to how they encounter one another. Tom if I may go back what is the essential difference between the egg and the sperm I think we will have an idea of what an egg is at least a ham. But but how do the male and female elements in this process. And this surely is the progenitor cells are very much alike. But the presumptive egg cell and large is considerably while the presumptive sperm cell intact

undergoes a shrinkage and a transformation into a tadpole like structure. But the egg cell can grow until it inside the ovary the female and in some animals such as the ostrich until it's many inches in diameter. Birds and sharks and many other animals are exceptional and having large eggs. The more usual size of neighing is about a tenth of a millimeter in diameter. That would be the size of an object just visible to the unaided eye. It would be the size of a dot. You might make another piece of paper with a very sharp pencil. So that's a sort of prayer. Physical characteristics of the egg and sperm now. I guess the next question one might ask would be how does the right write and a start on the process that this is another of your

interests evidently. Yes well the right wing is at rest until it encounters the sperm. These two cells unite. How does the sperm know that it's found an egg. Doctor time. Well it has what we would call recognition chemicals. That are adapted to receptor chemical substances that are on the surface of the egg. Actually the process is highly specific sperm and egg won't attach to each other unless they belong to the same or closely related species. Sperm will not attach to other cells of the body but the tissue cells other than the eggs. But just a Sikh saw the egg. This means it doesn't that the sperm can move

around but the egg got really tall. That's correct. The sperm has a motel organ long tail which will propel it about. And so it can encounter the egg the question is Is there an attraction between egg and sperm. Well in some species of animals lower animals and in some plants attractive influences have been demonstrated. But in higher animals. And mammals and even many of the higher marine animals there's no real evidence for such attraction. On the other hand since there are usually millions and sometimes billions of sperm liberated one time the chance of. Encounter by accident is very great. So that in a strange way if if one may be a little popular the egg sperm encounter is in a curious gym Similar to

go meets boy in that the boy seeks out the girl and the guard provides some means of attraction in order to show one that she is a girl and to know that she is the girl of the sort that the boy Mike liked to meet. Yes exactly they are adapted to one another and we do no examples in lower animals where this adaptation is on an individual basis so that the sperm may refuse to night eggs which is not well adapted. So do I. Time once the sperm has found the egg then there is some process of fertilization which must be of interest to you. Yes the details of this fusion is something that has to be studied with the aid of high

powered microscopic instruments such as electron microscope. One needs devices. For slicing an object as I mentioned was it was a dot on a piece of paper slicing that into thousands of thin slices to examine in detail the process by which these two unite and yet I think it was fascinating as you point out that with your experimental techniques you can actually see the eggs and the sperm and you can physically see them and you can take photographs of them and one can obtain a very physical picture I'd like to do a little more on some of those experimental methods if you. Yes as I mentioned one can enlarge these objects and study them in detail. One can also extract various chemical substances from the eggs and from the sperm and study their interactions by themselves. And in this

matter we can specify that the egg and sperm unite by virtue of the fact that the particular chemical substances on their surfaces are adapted to another chemically structurally. And so we explore these substances chemically but the primary problem at present in which we are engaged and in which many developmental biologists are engaged. The primary problem is that activation and of differentiation. So I guess as you've said we've we've described very roughly what the eggs and sperm alike and how we know this through our experimental techniques but the important part the things that you are looking for in our Are the problems of activation and differentiation Dr. Tyler what do you mean by those two words by

activation we mean the turning on of the machinery that transforms the egg to the adult animal differentiation is essentially to becoming different of different parts of the developing egg the formation of the various different kinds of tissues and organs of which the adult the animal is composed. At what stage and hard does this activation come about. Talk to time immediately upon fertilization activation occurs and one can detect that neatly upon the union of egg and sperm. Great increase tremendous increase in the synthesis of new chemicals new substances particularly proteins. That is going on so that immediately the sperm starts to encounter the egg things start to happen and all these

processes these plans that have remained locked in the egg are suddenly put into action and we know what it is that causes this to happen. Yes one can say that in the nucleus of the egg and that of the sperm you have the complete set of plans for the future animal. In the form of the substance that we call it is actually right going to be a gas and D and A for short. You know these plans are read piecemeal throughout development certain plans at the early stages other plans later stages and different regions of the DNA as we say different DNA molecules in different parts of the developing embryo. When you say the read but read piecemeal Dr. Tyler do you mean that they it is not like a book where one turns from page to page to page but that they are read in a

sense at random. They're not read at random and it means they're there read a very rigid sequence. And there's a departure sequence of reading then a very abnormal kind of organism develops if any develops at all. But the DNA represents the so-called master plans and master blueprint the actual working plans are transcribed from the DNA in the form of a very similar kind of chemical called Ribot nucleate acid. And in brief RNA in a particular form of RNA called messenger RNA so many copies of the working blueprints the messenger RNA are put out to transcribe different regions of the DNA of the nucleus.

Could you describe what this transcription process involves. The transcription process is simply the assemblage. Mirror Image type of molecule from the master molecule so that it as you say you run the master plans are stored in the DNA and the RNA is in a way brought up to it and copies these plans to the component parts that go to make an RNA brought up to the DNA and assembled there in a sort of mirror image of the DNA and many copies are made for any particular region of the DNA that's being transcribed and one can say from the investigations that have been done so far that the working blueprints for many hours of early development are already present in the unfertilized egg

and upon fertilization. These are set to work. They remain in a inactive condition a mask condition and the unfertilized egg and upon fertilization are put to work and assemble new proteins that are needed for early stages of development. If I may go back a little. Dr. Tyler your original remarks about hereditary the blueprints are Pockley in the spring and parking in the eggs. I take it that right. Ordinarily normally fertilized egg both are used. However it's quite possible to initiate the development of an egg without the sperm by chemical means in which case then only the blueprints in the egg nucleus for use in that case the animal has only the critics of its mother.

Has only the characteristics that were carried in the nucleus of the egg supplied by the mother but not necessarily all expressed by the mother. And also it's possible to remove a nucleus from an egg and simply give the egg not to get egg the sperm nucleus which case it would have the characteristics supplied by that. But normally it would be a developing it would be a product of both and approximately equal amounts. I was interested in your mentioning hours in terms of the time scale in which these processes start. Can you give us a little more about the kind of times that are needed for these things to happen and how long the problem of process of activation is in progress for. Well in lower animals one may proceed from an egg to a swimming larva in a matter of less than a

day course in higher animal takes much longer. But I think as is probably commonly known most of the features that say human development already. President and developed in the first couple of months. So that the first few weeks of human development in which the most tremendous changes take place by that of course you mean Dr. Tyler the first few weeks of the embryo long before the baby has been born and human. Yes exactly. So that when when Braun the baby is pretty well much what he's going to be. And I think this brings us to the next aspect you were talking about the problem of differentiation. What do you mean by that. By that we mean the process sees whereby different regions of the body specific times

various kinds of tissues are formed by the lens the heart anything. And for this we now know that the particular working blueprints have to be laid down in the specific regions of the developing embryo. How this is done is something which none of us really know but which we are exploring. What are they or what we anticipate. May come out of this kind of investigation. Aside from an intrinsic interest all of this is that someday one may hope to improve development in one way or another.

One may also think in terms of controlling reproduction in a quantitative sense stuck in time I'd like care if I may just to return to that fascinating point you were making about the development about different things growing within it. Take a human baby. Could you tell me a little bit about the fact that when a baby is born certain things are different from from him as he grows older and how that that really works. And your differentiation. While in development of all organisms after fertilization the new cell fertilized egg undergoes a series of cell division. This continues throughout life. There are trillions of cells in the adult organism and this process and the division of each of the fertilized egg starting from the fertilized egg into two. But

this would be a process where you would have trillions of objects that would be essentially alike. However as we've indicated presently in early development different parts become different different regions develop into different kinds of structures. I see and so this gets us back to the place where I so rudely interrupted you and where mistaking ask could we use some of these ideas to control to see things like that. Well obviously if a developing individual is making the wrong kind of protein as a result of having the wrong DNA like sickle cell anemia DNA. We could attempt to repair this by providing the right DNA or perhaps more readily by getting the developing organism the proper working blueprint. It has information to make the right kind of hemoglobin and do the same kind of thing for various kinds

of inherited biochemical deficiency. What about Dr Tyler this very romantic idea of constructing a new man a superman. Well obviously if you can repair inherited biochemical deficiencies and you can hope to go beyond that we can assume that all of us are really deficient with respect to some ideal super individual it was ideally adapted to his environment that is strong or brainy or more resistant to disease than any known at present. And conceptually it should be possible. By supplying the kinds of information. What synthesised it's a particular approach to improved development in that sense. We could conceive producing individuals that are adapted to cope with the exigencies

of the environment. I see. And so there we have some of the possible ounces to these age a general questions that the child asked the man and the man asks nature. However it isn't simple. We certainly don't have all the answers but we have seen that some of the basic processes of living things such as cell division are common to all and that many animals in fact most animals go through a remarkably similar development processes. We've talked a little bit about matters of attraction how the tiny sperm cell often present in billions can actually swim and moves itself to find an egg cell and how it knows that that is an excel in that it's a rock run and we would learn to possibly have some of the most interesting part of it how this development then follows a precise set of plans blueprints a few like blueprints of stock things going at the right time

turned things or when their course is finished. It's not really the sort of thing that a child r asks when he says Where did I come from. But these are the things that biologists are asking and these are some of the places that this research can take us to some ideas of the control of hereditary disease the repairing of defects the construction of people who can be disease resistant. And possibly in the far far distant future. The idea that we might be able to build a better type of man. Thank you Dr. Tatar. This was about science with host Dr. Peter listen and his guest Dr. Albert Tyler join us again for our next program one doctor less amenable heated discussion about the nature of life about science is produced by the California Institute of Technology and is originally broadcast by station KPCC in Pasadena California. The

programs are made available to station by national educational radio.