From Giessen to Toulouse: 20 years in domestic animal cytogenetics

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From Giessen to Toulouse: 20 years in domestic animal

cytogenetics

I Gustavsson

To cite this version:

From

Giessen

to

Toulouse:

20

_years

in

domestic animal

_cytogenetics

I

Gustavsson

Swedish

University of

Agricultural Sciences, Department of

Animal

Breeding

and

Genetics,

S-750 07

_Uppsala

7, Sweden

(Proceedings

of the 9th

_{European Colloquium}

on

_Cytogenetics

of Domestic

_Animals;

Toulouse-Auzeville,

10-13

_July

₁₉₉₀₎

Twenty

years have now

_passed

since the first

_{European meeting}

on

_cytogenetics

of

domestic animals was held in Giessen in 1970. I remember that

_meeting

_very well

because it was one of the first international

_meetings

I attended. A small _group

of

_people

came

_together

and for most of us it was _very

_{exciting -}

as I

_hope

this

meeting

is for the _young

_people

here - because we knew each other

_only

_by

name and

according

to what each had

_published.

Most of those individuals in

_Europe

that we

today

consider as

_pioneers

in our field

_{participated.}

The

_period

before our series of

meetings

started had been

stamped

by

important

discoveries in the human field. The

correct human chromosome number had been established in 1956

_(Tjio

and

_Levan,

1956)

and,

in

_1959,

Down’s

_syndrome

was associated with

_trisomy-21

(Lejeune

et

al,

1959)

and Klinefelter’s

_syndrome

with the sex chromosome constitution XXY

(Jacobs

and

_Strong,

_1959).

In our field as

well, important steps

had been taken:

XX/XY

chimerism

_(Ohno

et

_al,

₁₉₆₂₎

and autosomal

_trisomy

_(Herzog

and

H6hn,

1968)

had been found in

_cattle;

the first

_reciprocal

translocation had been described

in

_pig

_(Henricson

and

_Backstrom,

₁₉₆₄₎

and the

_1/29

translocation in cattle had been associated with decreased

_fertility

_{(Gustavsson, 1969).}

The initiative for the first

_{European Colloquium}

was taken - as all of you

probably

know -

_by

Professor GW

_Rieck,

who retired several years ago. He

made,

exemplified by

communications at several of our

_colloquia,

an

_immensely

valuable

contribution of our

_field,

_{particularly by associating}

different malformations and

diseases with chromosome aberrations. After some

_irregularity

in the

_beginning,

the

latest

_meetings

have been held _every two _{years (table I).} The

_approximate

number of

participants

and communications

_have,

since the first

_meetings,

been

_fairly

constant

but the number of communications in different

subjects

has varied. When I look at

the

_people

here

_today,

I see _many well-known faces.

_{Many people}

have _gone and new

_people

have come, but there is a small nucleus which has attended several

meetings.

So there are

_evidently

laboratories which have been able to maintain a

continuously high

level of

_activity

in

_spite

of

_changes

in the economic situation as

well as

_changes

of trends in

_genetics.

If we look at the communications

_presented

over the _years, we find that the

participants

of the

_{European colloquia}

to a _very

_large

extent. This concerns

partic-ularly

the identification and detailed

description

of mitotic chromosomes. The

chro-mosomes of most domestic animals present

great

problems

in identification due to

high

chromosome numbers and chromosomes of similar

_{morphology. Development}

has therefore been troublesome

sometimes,

eliciting

many heated discussions. Some

of us still remember the controversies about the identification of the X chromo-some in

_pig

that started at the standardization

_meeting

held in

_Reading

in

_1976,

which were

_{accompanied by}

heated discussions and the

_slamming

of doors. The

first

_{European colloquium}

was hindered

_by

the lack of

_banding

_techniques

for the

description

of normal and abnormal

_{karyotypes. However, already}

at that

_meeting

attempts were

_being

made to overcome the identification

_problems.

One

_technique,

the so-called

_{’pencil-follower technique’}

for

_measuring

chromosomes was described

in the _very first scientific paper

(Paufler,

1970). Unofficially

at that

_meeting,

KM Hansen from Denmark

_{demonstrated,}

if I remember

_correctly,

the first

_Q-banded

cattle chromosomes. At the

_meeting

in Giessen in

_1975,

information about banded chromosomes of several domestic animals was available and was

fruitfully

collated

into

_agreements

on international standards in

_Reading

in 1976

_(Proceedings

of the First International Conference for the Standardisation of Banded

_Karyotypes

of Domestic

Animals,

1980).

The information has increased

and,

in addition to

the standard

_{C-, Q-, G-,}

R- and

_T-banding

_techniques

_{(Gustavsson, 1980),}

which have now been used for several _years, the introduction of different fluorochromes

cytogenetic analysis.

High-resolution

techniques

have been established and even more detailed standards for the domestic animal chromosomes have been

_agreed

to

(ISCNDA, 1990). Application

of different

_{banding techniques}

has

_{provided insights}

into the structure and

_organization

of chromosomes

_and,

with the

_increasing

results

on the molecular

_level,

our

_knowledge

can be further increased. We are thus in the

position

of

_having

a

_good

set of somatic chromosome

_techniques

which enable iden-tification of

_single

normal chromosomes as well as

_rearranged

chromosomes. After

this

_{’chromosome-stretching’}

_{era, it} is now

_extremely

_urgent

that we

_try

to use this

information more

_practically.

It is therefore with

_great

pleasure

that I see _many

scientists now

_turning

to the gene

mapping

field. The detailed chromosome

infor-mation should also be

_applied

to clinical

_{cytogenetics.}

It is also

_{quite important}

that

we continue to

_develop

our

_present

_banding

standards into

_{high-resolution}

ones. In

this context, we should not

_forget

the new so-called chromosome

painting

tech-nique

(eg,

Pinkel et

_al,

_1989),

which will

_probably

be _very useful for identification of chromosome

_segments

once

chromosome-specific

libraries have been established.

Even with new

_banding

_techniques,

I

_{think, however,}

that

_karyotypes

such as the

bovine ones will continue to _pose

_{important analytical problems}

in the future. A detailed

_analysis

of the

_karyotype

of an individual is _very

_{time-consuming and,}

in

my

opinion,

still to some extent unreliable. In this

_context,

automated or

semi-automated

_analysis

will be of

_great

_help.

I can tell _you that even in

_pigs

we

sometimes have

_{problems identifying existing}

aberrations. Caution is therefore

to be taken about the

_reliability

of incidences of chromosome aberrations in

large samples

of animals

_{investigated during}

a short

_period

of time. To be able

to

_{identify deviations,}

there are several conditions to

_fulfill,

_including

extensive

training

of the

analyzer

and detailed

_knowledge

of

_single

chromosome

_pairs

and their

_banding

_patterns.

It is _very

_{exciting that,}

_{by comparing banding}

_patterns

of different

_species,

we now have the

_possibility

to discern

_karyotype

evolution. In

some _groups of

_animals,

like the

_{family Bovidae, karyotype}

evolution has involved

centric

_fusions,

for the most

_part,

while in a _{group like}

Equidae

there has been

more

_{complex karyotype}

evolution. In this

work,

the

_expansion

of gene maps will

speed

up progress.

So,

one

_hopes

that in the near future we will know how the

karyotypes

of our domestic animals have evolved and also how

_karyotype

evolution

has

_proceeded

in domestic and wild

_species.

This increased

_knowledge,

in _turn, can

help

us make clinical

_predictions

and

_anticipate

the

_phenotypic

outcome of

_zygotes

with

_{chromosomally}

unbalanced

_karyotypes.

The number of chromosome aberrations described is still low and our

_knowledge

of their

_etiology

and incidence in different domestic animal

_populations

_{is very poor.} To a _very

_large

_extent, this is

_definitely

due to the fact that malformed

animals,

animals with

_{reproductive problems, abortuses,}

stillborns and so on

only rarely

come to

_{investigation.}

I have found that the

_only

_way to obtain

_{cytogenetically}

interesting

material is to have

_good

connections with

_{veterinarians,}

breeders and farmers. This can

only

be achieved

by

reiterated information of _your work and

interests. It is also

_important

that you

always

show an interest in the

_problems

in

the

_field,

even if _you think

_they

have no

_cytogenetic

basis.

_Only

a few malformations

have been ascribed to

abnormal

chromosome constitutions.

_Lately,

I have wondered if

_perhaps

we have been too _eager to

_expect

dramatic

_{phenotypic changes}

due to

phenotypic

effects was shown

_{by Mayr}

et al

₍₁₉₈₅₎

in trisomic

_cattle,

and

_also,

in our routine

_analyses

in

_{Sweden, by}

a recent incidental

_finding

of a deletion in

a Blonde

_{d’Aquitaine}

heifer with normal

_body

conformation. We now also have cases of translocations in

_{pigs producing}

stillborn and even live-born

_piglets

with

unbalanced

_karyotypes,

but nevertheless

_having

a

_fairly

normal _appearance. Most

aberrations have been found in animals with low

_fertility

_but,

if _you look in the

literature,

you will find that a

surprisingly

high

number has been found more or less

_{incidentally.}

Such aberrations are centric fusion translocations

_including

1/29 -

already

known before this series of

_colloquia

was started - but nevertheless

described and discussed at all

_meetings

since then. The incidence of chromosome aberrations to be found in a

_population

is

_primarily

due to the interference of

chromosome mutation rate and selection _pressure.

_Very

little is known of mutation

rate. Of course we have some

_knowledge

from the routine

_screening

of cattle for the

presence of

1/29

translocation. In

Sweden,

at

_least,

_trisomies,

for

_{example 60,XXY}

and

_60,XYY,

_appear to occur at a lower incidence in cattle than in humans.

It is therefore

_{important that,}

in the

_future,

we

_’map’

different

populations

for chromosome constitution and

_existing

chromosome aberrations. References have been made to human

_cytogenetics

at all of the

_meetings.

We

_should,

of course,

consider observations and results and

adapt

the new

techniques

to our

field,

but we

have to

_recognize

the

_big

differences between human and domestic animals and also

among different domestic animal

species.

Aberration incidence is such a character.

It is

surprising

that so little has been

reported concerning

meiosis and

chromo-somal

_polymorphism

in domestic animals.

_Throughout

the

_history

of our

_European

colloquia, only

few

_reports

have been made on

_meiosis,

other than the work

_by

David

_Logue

₍₁₉₇₇₎

on Robertsonian translocations

presented

at the

_colloquium

in

Paris. Detailed meiotic studies

_using

conventional

_techniques

_(eg,

Evans et

_al,

₁₉₆₄₎

can

_give

information about chiasma

_{localization, segregation}

and so on. With the

synaptonemal complex analysis

(Counce

and

_Meyer,

_1973),

_{interesting pairing}

con-ditions can be evaluated.

Doubtfully

identified aberrations on the somatic cell level can and should be substantiated

_definitively

with

_{synaptonemal complex analysis,}

before

_they

are classified as aberrations.

_{Polyniorphisms,}

such as Y-chromosome

variations,

centric fusion

translocations,

variable amounts of heterochromatin

par-ticularly

centromeric,

and

_{qualitatively}

and

_{quantitatively}

variable NORs

_(nuclear

organizer

regions),

are common in different domestic

_species.

The extensive

vari-ation of centromeric heterochromatin in cattle was

_pointed

out

_by

Di Berardino and coworkers

₍₁₉₈₀₎

at the

_{Uppsala meeting}

which led to later work

_being

done in other

_{species. However,}

there are no

_comparative

_{investigations}

of

breeds,

popula-tions and so _on, and the

practical

utilization of

_{polymorphisms}

in

_paternity

_tests,

genetic relationships

between

_populations

and for different

_experimental

_purposes has not

_yet

been

_explored

at all. The

_{phenotypic effects,}

if there are _any, should be identified. To the _group of

_{polymorphisms}

should also be added

_fragile

_sites,

which are still

_unexplored

in domestic animals.

_Why

such

_phenomena

as meiosis

and

_polymorphism

have attracted so little interest is difficult to understand. One

reason _may be that

_grants

are

_{given particularly}

to

_projects

with a

_predictable

expected

economic

_gain.

Very

little is known about mutation rates.

_Undoubtedly,

there are differential

geographical

areas,

species,

breeds,

etc are

_compared.

The mutation rate can, to

some

_extent,

be revealed

_by

studies of chromosome breaks and sister chromatid

exchanges.

I think this will be a new

important

area in which a lot of interest

will be shown in the future. With the

_increasing

concern for the environment and

high-quality

food

_production,

it will be necessary to

_identify

the roles of different

mutagens

in the environment of domestic animals and ascertain their

_importance.

As

_early

as the Giessen

_meeting

in

1975,

Lojda

and coworkers

(1975)

reported

on such

_aspects

but _very few other researchers have carried out similar studies.

Personally,

I think it is also

_extremely

_urgent

to

_clarify

the

_significance

of the

group of

unspecific

aberrations called chromosome gaps, achromatic

segments,

constrictions and so _on, which are often mentioned in connection with clinical

findings.

In addition to clinical

_{cytogenetics,}

we can

today distinguish

two other

_fields,

viz _gene

_mapping

and

_{embryo technology, developed during}

recent _years.

_Although

detailed

_physical

gene maps have been available for the human genome, it took

a

_long

time before similar _maps started to be

_developed

in domestic animals.

Good _surveys of the

_development

of the field have been

_{given particularly by}

the

Toulouse group at several of our

_European

colloquia

(Echard

et

al, 1982,

1984).

In addition to

_being

_{very time} and labor

_{consuming, family}

studies of chromosome

segregation

correlated to _{studies of blood groups,}

_proteins

and _enzymes most often

failed. Somatic

hybrid

studies gave

important

results for the domestic

_pig,

while similar work in cattle has

_appeared

more difficult due to chromosome identification

problems.

The most

_{promising technique}

until now is in situ

hybridization which,

by making

use of DNA

_{probes, gives}

more detailed information.

_Already

at the

meeting

in

_Uppsala

_(1980),

_{chromosomally assigned}

_genes were

_reported

and more

detailed _gene localizations will be described at the

_present

_meeting.

Of _course, we

in this field follow what has been described

_{by genetic mapping but,}

as one of _my

coworkers will show

_{later, unexpected findings}

can occur. A more distant

_approach

is

_genetic

transformation

_by

introduction of DNA

_coding

for a known gene into a

pronucleus

of a fertilized ovum. The material is sometimes

_integrated

into one or more chromosomes.

_{Probably, however,}

we have to learn more about chromosome

structure and

_organization

before

_genetic

transformation can be

_successfully

used as a tool in

_applied

_breeding.

If _you have

_recently

attended

_general

and human

_genetics

meetings,

I _{suppose you} have noticed that there is an

approach

to

_cytogenetics

at

the molecular level. I think we also have to _{go in} that direction - it will be

_profitable

for us and

_cytogenetics

is

_by

nature

_closely

linked to molecular

_genetics.

Molecular

genetics

is the fashion in

_{genetics today}

but there will

_be,

as

_maybe

some of _you

fear,

no risk of a

_{disappearance}

of our field. In the

_{future, cytogenetics}

will continue

to be a _necessary field - and the

_{cytogeneticists}

will be a rare _{group due} to the skillfulness and

_experience

needed to achieve

_good

results. We have many

problems

to

_study

on the

_cytogenetic

level and more detailed information on these

problems

can be obtained

by cooperation

with molecular

_{cytogeneticists.}

Embryo

technology has,

to some

_extent,

been

developed

in

_conjunction

with

cytogenetics.

By micromanipulation,

nuclei or

_pronuclei

can be withdrawn or

inserted into ova. In this _way, it is

possible

for instance to

_{produce polyploid}

embryos,

to obtain

_crossings

of

_distantly

related

_species

and to learn about the

produced by fusing

different

_embryos

or

_injecting

cells into the inner cell mass of

the

_{embryo. Particularly interesting}

is the culture of

_pluripotent

cells derived from

embryos (Notarianni

et

_al,

_1990).

This work will

_provide

a link to the transfer of

foreign

genes. The most

_{important practical application}

of

_cytogenetics

in

_embryo

technology has, however,

hitherto been the

_application

of

_{cytogenetic techniques}

to

_{embryo sexing.}

For a

_long

_time,

direct observation of the sex chromosomes in

split embryos

or a few

_surgically

removed blastomeres was the

_{prevalent technique.}

However,

since it often failed due to the absence of divisions in the collected

cells, together

with the deleterious effect the

_manipulation

had on the

_embryo’s

survival,

the

technique

is now out of mode.

Instead,

in situ

_{hybridization techniques}

appeared

and several different

_{Y-specific probes}

became available.

_Although

the in situ

_techniques

now more or less have been

_{replaced by}

the PCR

_(polymerase

chain

_reaction)

_technique,

based on molecular

_{amplification}

of a

_Y-specific

_sequence

visualized

_by

_{electrophoresis,}

in situ

_{hybridization}

with certain

_probes

can still find

application

(Schr6der

et

_al,

_1990).

The

_development

of domestic animal

_{cytogenetics,}

to a _very

_large

_extent, has

been

_dependent

_upon the

_availability

of _support funds. It has

_always

been difficult

to obtain

_grants

for

_studying

basic

_phenomena.

Most often it has been necessary

to offer a

_possible

economic

_advantage

to

_{get grants}

for a

_{project. Therefore,}

I

personally

think that clinical

cytogenetics

for a

_long

time will remain the backbone of our field due to its

_importance

for

_{veterinary diagnostics}

and for the eradication

of

_extensively

distributed chromosome aberrations

_causing

reduced

_fertility.

There

is

_{still, however,}

an

_{unfamiliarity}

about the

_importance

of

_cytogenetics

and how to

integrate

it into new methods of animal

_production.

It is essential that we educate

farmers,

veterinarians and other

_people

involved in

_breeding,

but it is also _necessary that we learn the details of animal

_breeding.

Although

these

meetings

have been

_arranged

particularly

for

_Europeans

_working

in the field of domestic animal

_{cytogenetics,}

we

have,

since the Paris

colloquium

(1977),

been

_happy

to see an

_increasing

number of

_colleagues

from other

_parts

of the

world

_attending

our

_colloquia.

At most

_{meetings -}

indeed as of the first

_colloquium

in Giessen

₍₁₉₇₀₎

with Alfred

Gropp

(1970) -

we have also been

pleased

to

_enjoy

the _company of

_outstanding

research workers from other

_specialized

fields. I think that

_inviting

such

_specialists

has been a

_good

idea because it has

_given

us some

knowledge

of what is

_going

on in other fields. We have obtained new ideas to be

applied

in our field and the _experts invited have also

_given

us sound advice. I think

few

_people

here

_really

understand how much a _person like Charles E Ford has meant

to the

_development

of domestic animal

_{cytogenetics.}

Other

_outstanding

individuals who have

_participated

are P

_Burgoyne,

A

_Chandley,

K

_Fredga,

J de

_Grouchy,

K

R6nningen,

M

_Seabright,

TC Smith and C Weissman.

The

_organization

form and the existence of the

_{European cytogenetic colloquia}

have been discussed on different occasions. Some

people

have

thought

that the

co-organization

of our

_{cytogenetics meetings}

with other

_meetings

would evoke an

increased interest in

_cytogenetics

for

_people

in other fields. The

_change

of the North American

_{cytogenetics meetings,}

which had

_previously

been subsections of

dairy

science and animal science

_meetings,

to a more

_independent

_state,

_however,

supports

the consideration that our

_present

_meeting

format is still the best. At the

to

_English

as the common

_language.

I also remember a communication

_given

in

Italian and

_directly

after that someone claimed to

_give

his _{paper in} Austrian. Since

most of us do not have

_English

as our maternal

language,

our

_vocabulary

is often

not

_{highly advanced,}

which can sometimes _pose a

problem.

I have noticed that

native

_{English speakers}

often start

_using

unusual words in discussions. This can be

a _way to more

_{clearly specify}

a

_problem,

but can also be a _way to

_prevent

_people

from

_{participating}

in a discussion. Sometimes communications have been

_given

in

American or Australian

_jargon

almost

_{incomprehensible}

for many of us. Then _you

start

_wondering

about the scientific content...

It _may be a

_pity

that the

_proceedings

are not

_published

in

_widely

circulated

journals. However,

limited circulation of

_proceedings

has the

_advantage

that more

incomplete

observations and observations of restricted interest can be

presented

and discussed in informal _ways. If an author thinks his communication is of more

extensive

_interest,

he has the

_possibility

to

_publish

his _{paper in e!tenso in} a

_widely

circulated

_journal,

a

_possibility

_many

_people

have used

_through

the _years.

It is very

important

that we

always try

to maintain an

acceptable

scientific level

in our work - each

_experiment

must have a _proper

_design.

There have been

ten-dencies towards failure at a few of the earlier

_meetings,

even with communications

given by people

considered to be

_experienced

in the field. I think _{it is very}

impor-tant that we

carefully

discuss such

things

and _not, due to some sort of

_courtesy,

disregard

them. For

_{inexperienced people}

in our

_field,

it is _necessary to learn how

to do

_good

work. It is also

_important

that

_people

in other fields

_recognize

us as

honest and serious research scientists.

Summarizing

this short

_review,

it can be concluded that the

_development

of

genetics is,

as we all have

_noted,

_very fast and we all have

problems

keeping

up with

developments.

Ten _{years ago,} Hsu

₍₁₉₇₉₎

wrote in his book:

&dquo;Perhaps

one of these

days

biologists

will be able to _compare two

_species

_by

_reading

_{their gene}

_alignments,

base

_{pair by}

base

_pair,

_along

each chromosome.&dquo; At the

_{Uppsala meeting,}

Rieck

(1980)

considered this to be a

_{utopia. Nevertheless,}

we are now close to that

_point

and we can read the base

pair

sequence, at least for small chromosome

_segments.

The

_{European colloquia}

have been

_important

milestones in the

development

of domestic animal

_{cytogenetics,}

not due to

_important

new

discoveries,

but because of

the fact that

_they

have served as summaries and have been occasions for discussions

of

problems

of mutual interest on both

_public

and

_personal

levels. I

_hope

that this

meeting

will also have a

_friendly,

familiar

atmosphere

and

provide

the

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