SYNAPTONEMAL COMPLEX-ANALYSIS IN GOATS CARRYING THE 5/15 ROBERTSONIAN TRANSLOCATION

Original

article

Synaptonemal complex analysis

in

_goats

_carrying

the

_5/15

Robertsonian

translocation

MEJ

Amaral

W

_Jorge

₂

1

Instituto

de

Biociencias, Departamento

de

Genetica,

UNESP,

Campus

de Botucatu, 18618-000, Botucatu, Sdo

Paulo;

2 _{Instituto de Ciencias}

Biológicas, Departamento

de

_{Biologia Geral,}

Universidad Federal de Minas

_{Gerais, 31,}

270-010 Belo

Horizonte,

Minas

_Gerais,

Brasil

(Received

24

_February

_1993;

accepted

21

_February

₁₉₉₄₎

Summary -

Synaptonemal complexes

were

analysed by

electron

_microscopy

in 2 bucks

heterozygous

for the

_5/15

Robertsonian translocation. The cis

configuration

(free

homo-logous

5 and 15 chromosomes on the same side of the

5/15

translocated

chromosome)

was

found in all 50 cells examined. This feature is considered a

_prerequisite

for the

development

of balanced _gametes. No association between the sex bivalent and trivalent was observed.

meiosis / synaptonemal

complex

/

trivalent

_/

Robertsonian translocation

_/

goat

Résumé - _L’analyse du _{complexe synaptonémique} de 2 boucs porteurs de la translo-cation robertsonienne

_{5/15. L’analyse}

du

_{complexe synaptonémique}

a été

effectuée,

en

microscopie

électronique,

chez 2 boucs

_{hétérozygotes}

_pour la translocation robertsonienne

5/15.

La

_{configuration}

cis

_(chromosomes

_homologues

5 et 15 situés du même côté du

chromosome-transloqué

5/15)

a été trouvée dans les 50 cellules examinées. Cette

carac-téristique

est considérée comme une condition

_préalable

au

_{développement}

de

_gamètes

équilibrés.

Aucune association entre le bivalent sexuel et le trivalent n’a été détectée.

méiose

_/

_{complexe synaptonémique}

_/

trivalent

/

translocation robertsonienne

/

chèvre

*

Correspondence

and

_reprints:

1109 Southwest

_{Parkway, Apt 1702, College Station,}

INTRODUCTION

Electron

_microscopic

_(em)

_analysis

of

_{synaptonemal complexes}

_(SC)

in the meiotic

cells of domestic animals

_carrying

chromosomal aberrations

_began

with the works of Switonski et al

₍₁₉₈₇₎

and Gabriel-Robez et al

_(1986).

Karyotype analysis

of 2 Saanen male

_goats

with 2n = 59 chromosomes indicated

the _presence of a submetacentric chromosome. The

_G-banding

technique

was used

to

_identify

the marker chromosome as a fusion of chromosomes 5 and 15. Little research has been documented

_concerning

SC in

_goats

_possessing

either normal or

translocated chromosomes. To

_investigate

the effect of the

_5/15

translocation on the

reproductive

capacity

of the

_heterozygous

_animals,

SC formation and the behaviour of the trivalent

_5/15;

_{5 ;15}

was studied at the

_pachytene

_stage

of meiosis.

MATERIALS AND METHODS

Two Saanen male

_goats

_{(Capra hircus),}

both

59,

XY,

t(5 ;15)

heterozygous

for the

translocation were studied. Hemi-castration was

_immediately

followed

_by

testicular

dissection with a

scalpel,

in Hank’s medium.

The

_preparations

of

_{microspread samples}

were made

according

to the

technique

presented

by

Solari

_(1980).

A

_droplet

of the testicular cell

_suspension

was added

to

_{approximately}

5 ml of a

0.5%

NaCI

_hypotonic

solution. The

_spread

nuclei were

then

_picked

up

by touching

slides

pre-coated

with

plastic

film on the surface of the solution. The slides were

immediately

immersed in a

Coplin jar containing

SDS fixative

_(4%

_{paraformaldehyde}

and

0.03%

_{SDS, pH}

8,

adjusted

with sodium tetraborate

_buffer)

and incubated for 5 min at room

_temperature.

The slides were

then held on the surface of

0.4%

Photoflo, pH

8 for 30 s and allowed to

_air-dry.

Silver nitrate

_staining

was

performed

as described

by

Howell and Black

(1980).

Nuclei were selected

by light

_microscopy

and covered with

50/75

mesh

grids.

The

plastic film,

with the attached nuclei and

_grids,

was detached from the slide

by

floating

on water and collected with resined paper. Under em, the

magnification

was 1 600 x.

_Micrographs

were

enlarged

5 x. The SC

_lengths

(mm)

were measured

individually.

Intact nuclei

_containing

a

complete

SC set were used to construct

karyotypes.

The normal autosomal bivalents were

arranged by decreasing

size and

aligned by

the kinetochore. Each trivalent

_5/15,

5 and 15 was

_put

in the

position

of bivalent 5

_(see

_fig

2

_below).

The XY bivalent

_occupied

the last

_position.

The trivalent

_5/15,

5 and 15 was

photographed individually

and

enlarged

4200 x _for

detailed

_analysis.

The

_position

of the kinetochores of the free

_homologues

5 and 15 was considered cis when the free kinetochores 5 and 15 were located on the same side of the

5/15

chromosome,

and trans when the free kinetochores 5 and 15

were located on

opposite

sides. In 50 cells

containing

the sex

bivalent,

the _presence or absence of association of the trivalent

5/15,

5 and 15 and the sex bivalent was

RESULTS

Twenty-seven

autosomal

_bivalents,

one autosomal trivalent and the sex bivalent

(figs

1 and

₂₎

were observed in

_spermatocyte

_preparations

from the

heterozygous

5/15

translocated buck

_(2n

=

59).

In all the

analysed

nuclei

(50),

the free

homologous

chromosomes 5 and 15

_paired

in the cis

_{configuration}

_(figs

3 and

4).

In the

_trivalent,

the

_{pericentromeric region}

of the free

_homologous

5 and 15

was not

_paired

at

_{early pachytene}

_{(fig 3).}

At

_{mid-pachytene, heterosynapsis}

was

observed between the

_{pericentromeric regions}

of the free

_homologues

5 and 15. At late

_pachytene,

the

_synaptic

_adjustment

was

complete

and the centromeric

tips

of the free

_homologues

5 and 15 were

completely paired

with the translocated

corresponding

arms

(fig 4).

The

kinetochores, however,

did not fuse and

_stayed

in

juxtaposition.

The trivalent

_5/15,

5 and 15 was not observed to be associated with the sex bivalent.

DISCUSSION

In this _paper, the trivalent showed the

_{pericentromeric region}

of the free

_homologues

5 and 15 not

_paired

at

_{early pachytene.}

Late

_synapsis

seems to be a characteristic of

the trivalents as is described in bovine

(Switonski

et

_al,

_1987),

and Lemur

_hybrids

(Moses

et

_al,

_1979).

In chinese hamster

_bivalents,

the centromeric

_region

is also the last to form SC

_{(Moses, 1977).}

The kinetochore of the free

_homologues

5 and 15

_paired

_{preferentially}

in the cis

configuration

with their

_homologue

_portions

in the

_5/15

translocated chromosome and were visible

throughout

the

pachytene.

Moses et al

₍₁₉₇₉₎

observed the same

phenomenon

while

_studying

trivalents in Lemur

_hybrids

under em. Data obtained

with

_Capra

hircus agree with the results of Moses et al

₍₁₉₇₉₎

who

_suggested

that both acrocentric kinetochores maintain the cis

_{configuration}

_{independently}

_during

synapsis.

This excludes the

_probability

of variable

_pairing

faces and leads to the conclusion that a

single

_pairing

face on the translocated chromosome determines

the

_plane

of SC

_assembly.

The cis

_{configuration}

was also found in the

rodent,

Sigmodon falviventer, by

light

microscopy

(Elder

and

_Pathak,

₁₉₈₀₎

and no

fertility

reduction was observed.

When the

_heterozygous

buck was crossed with normal

homozygous

or

hetero-zygous,

females,

there was no

fertility

reduction

_according

to

_Goncalves

_(personal

communication).

These data may be

interpreted

as an indirect

sign

of a non-random

segregation

of the trivalent chromosomes. Moses et al

₍₁₉₇₉₎

noted that the normal

fertility

rate observed in Lemur

_hybrids

in related to a mechanism which increases

the

_frequency

of balanced

_gametes.

In

_addition,

such a mechanism would

specify

the

_symmetric

_arrangement

of free

_homologues

of the trivalent at

_pachytene.

The

_hypothesis

which

_suggests

that the

symmetry

presented by

the translocated chromosomal arms _may influence the

_{configuration,}

either cis or

_trans,

should be considered. It may be well

accepted

that the more

asymmetric

the translocation

arms, as in bovine translocation

1/29,

the

_greater

the

_probability

of

observing

the

rats with

_t(10;11)

_(Elder

and

_Pathak,

₁₉₈₀₎

and humans with

_{t(13;14) (Luciani}

et

_al,

₁₉₈₄₎

_present

_very

_symmetric

translocated chromosomal arms.

Perhaps

the

trans

_{configuration}

becomes less

_probable

as observed if the chromosomal arm ratio

(long arm/short arm)

approaches

1.00.

There are

morphological

differences _among the trivalents that result from centric

fusion in

_{bovines, humans,}

rodents and

_caprines,

and

_they

_may influence the association with the sex bivalent. The variation in the

position

of the acrocentric

chromosomes

_neighbouring

the sex vesicle

_produces

free

_parts

with a

_stronger

tendency

to

_pair

with the sex chromosomes. This variable

tendency

could

explain

the variation which occurs in the

phenotypic expression

of

fertility

in men with

centric fusion

_(Johannisson

et

_al,

_1987).

Bouvet et al

₍₁₉₈₉₎

_suggest

that the absence of association

between

the sex bivalent and the autosomal trivalent could

explain

the

normal

_{spermatogenesis}

_{presented by}

cattle

_carrying

chromosomal

_{translocations,}

while mice and humans

_carrying

similar translocations are infertile due to the

presence of such associations.

In the

present

case, the trivalent was not observed in association with the sex

bivalent. In studies on humans

(Johannisson

et

_al,

₁₉₈₇₎

and mice

_(Forejt

et

_al,

1981)

it was assumed that the

reciprocal

and Robertsonian translocations may

bring

about either

_sterility

or

infertility

if the

unpaired

_autosomes,

or autosomal

segments,

pair

with the X chrosomome. The authors have

_suggested

that the

proximity

of the autosomal

_segment

with the X chromosome may interfere with its

inactivation _process

_{by harming}

the

_germinative

cell. This kind of association has often been found in infertile men with balanced Robertsonian translocation between

chromosomes 13 and 14

_(Luciani

et

_al,

₁₉₈₄₎

and 14 and 21

_(Rosenmann

et

_al,

_1985).

In all of the

_micrographs

_observed,

the

_phase

of

_unpairing

in the

_{pericentromeric}

region

of the acrocentric 5 and 15 was restricted to the

_beginning

of

_pachytene

when the Y chromosome had also started

_pairing

with the X chromosome.

ACKNOWLEDGMENTS

We would like to thank A

_{Solari, University}

of Buenos

Aires,

for

help

in the

technique

adaptation,

Y

_{Yonenaga-Yassuda,}

Bioscience

Institute,

USP,

Sao

Paulo,

for assistance in

the

_analysis

of the

_results,

EA

_Greg6rio

and MH Moreno, Electron

_{Microscopy Center,}

IB, UNESP, Botucatu,

for utilization of the electron

microscope

and CAPES for _support of the

_project.

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193-199

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