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.