SYNAPTONEMAL COMPLEX-ANALYSIS OF THE SEX BIVALENT IN GOATS

Note

Synaptonemal

complex

analysis

of

the

sex

bivalent

in

goats

MEJ

Amaral

1

W

_Jorge

₂

1

Institut de

_{Biociencias, UNESP, Departamento}

de

_Genetica,

Campus

de

Botucatu,

18.618-000

Botucatu,

Sao

Paulo;

Universidade

Federal de Minas

_Gerais,

Instituto de Ciencias

_Biologicas,

Departamento

de

_{Biologia Geral,}

31.270-O10 Belo

_Horizonte,

Minas

_Gerais,

Brazil

(Received

24

_February

1993;

accepted

7 March

₁₉₉₄₎

Summary -

Synaptonemal complex

(SC)

analysis

of XY

_pairing

in the _goat

_{( Capra}

_hircus;

2!z =

60)

was

_{investigated by}

electron

microscopy

for the first time in this _species.

_Synapsis

of the X and Y chromosomes

_{begins during}

the mid-late _{zygotene stage} as the autosomes

complete

their

_{pairing. Only}

a small _portion of the total

length

of the Y is

paired

with the

X chromosome at this time.

_By

the

_{early pachytene,}

almost 90% of the Y is

_paired

with the X. All the observed _stages of the sex bivalent

_pairing

showed the structural difference

between the differential and

_pairing

_regions. In the

_{pairing region,}

a

synaptonemal complex

is

_formed,

while in the differential

region

the chromosome axes remain free.

synaptonemal complex

/

meiosis _/ pachytene / XY bivalent _/ goat

Résumé - _Analyse du _{complexe synaptonémique} du bivalent sexuel chez la chèvre.

L’analyse

en _microscopie

_{électronique}

du

_{complexe synaptonémique}

(SC)

du bivalent

sexuel a, pour la

première fois,

été réalisée chez la chèvre. Le processus d’appariement

des chromosomes X et Y commence dans la deuxième _partie du stade

zygotène, lorsque

les autosomes arrivent en

fin d’appariement.

Seule une

_petite

_portion

de l’Y

s’apparie

à l’X. Au cours du stade

pachytène,

90% de l’Y est

_apparié

à l’X. Toutes les

_étapes

observées de

_{l’appariement}

du bivalent sexuel montrent une

différence

de structure entre

les

_{régions appariées}

et celles non

appariées.

Dans la

région d’appariement,

un

complexe

synaptonémique

se

forme

tandis _que dans la

région différentielle

les axes

chromosomiques

demeurent libres.

complexe synaptonémique / méiose _{/ pachytène /} bivalent XY

_/

chèvre

*

Current address:

_Department

of

_{Veterinary Pathobiology, College}

of

Veterinary

INTRODUCTION

The sequence of sex bivalent

pairing

at the meiotic

_prophase

in

_goats

was studied for

the first time in this

_species,

in

_preparations

of

_{spermatocytes}

obtained from males

at the

_beginning

of

_reproductive

age. The behavior of the X and Y chromosomes at the meiotic

_prophase

of

_goats

was observed

_by

electron

_microscopy

(em).

The

morphological changes

of the sexual

_pair

observed at

_pachytene

are described here.

MATERIALS AND METHODS

Testicular

_biopsies

were obtained from 2 Saanen

buck-goats

( Capra

hircus;

2n =

60).

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 to 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 the

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 or 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. The}

_{magnification}

under em was 4 200 x .

_Micrographs

were

enlarged

5 x . The XY bivalent was

_photographed

individually

for detailed

_analysis.

RESULTS

The XY bivalent was observed in 70

_{spermatocytes.}

Thirty

cells were

complete,

with 28 normal autosomal bivalents and one XY bivalent

(fig

1).

_Forty

cells were

incomplete

due to cellular

_disruption

and

_overlapping

of the

_grid

network but the

analysis

of the sexual bivalent was

possible.

The

_unpaired

sex chromosome axes showed

_thickening

and

_stronger

_staining,

allowing

easy identification

(fig

la).

Figure

2 shows the sex bivalent at mid-late

zygotene,

when the X and Y chromosomes are

starting

the

pairing

_process. At

early pachytene, figure

3,

the Y chromosome is almost

_{completely paired}

with the X. In

_figure

4a the sex bivalent is at

_{mid-pachytene, showing}

the X and Y full

pairing.

The sex bivalent at late

_pachytene

is

_presented

in

_figure

_4b,

_showing

the Y

chromosome still

_fully

_paired

with the X.

DISCUSSION

The X and Y chromosomes axes showed a distinct

_aspect

at

_pachytene,

and

_they

clearly

differ from the autosomal

_bivalents,

as can be observed in

figure

1. At

the

_synapsis

_process with

_only

a small

_part

of the Y chromosome

_paired

with the X

_{(figure 2).}

At the

_{early pachytene,}

almost

90%

of the Y is

_paired

with the X

chromosome

_{(figure 3).}

All the observed

_stages

of the sex bivalent

_pair

showed the structural difference between the differential and the

_{pairing regions}

described

_by

Solari

₍₁₉₇₀₎

for the serial reconstruction of the mouse XY

pair.

In the

_{pairing region,}

an SC is

formed,

while in the differential

_region

the chromosome axes are free.

SC formation is

_accompanied

_by

a

thickening

of the differential

_region

of the X and Y axes. This

_thickening

has

_previously

been observed in human

_{(Solari, 1980),}

Chinese hamsters

_{(Moses, 1977),}

and rats

_(Joseph

and

_Chandley,

₁₉₈₄₎

but its

meaning

is still unknown. In

_{spread technique}

_{preparations,}

this

_thickening

is

_rarely

substages

(Solari,

1980;

Greenbaum et

_al,

_1986).

_According

to these

_authors,

the

compaction

and dilatation of the differential

_region

characterize the

_early

and

mid-pachytene.

We can observe this feature in

_figures

2,

3 and 4. The late

_pachytene

is characterized

_by

’cracks’ in the differential

_region

_(fig

_4).

In

_goats,

at least 3

_{pachytene substages}

were

identified,

ie

early,

mid- and late

pachytene, considering

the

_changes

in the X chromosome differential

_region,

since the Y chromosome is

fully paired

with the X. The full

_pairing

of the Y axis with the X has

_already

been observed in other mammalian

_species,

such as rats

_(Joseph

and

_Chandley,

₁₉₈₄₎

and cats

_(Gillies

and

Cowan,

1985).

According

to Solari

_{(personal communication),}

such a

complete pairing

occurs when chromosome Y is very small in

comparison

to

ACKNOWLEDGMENTS

We would like tQthank A

_{S.olari, University}

of Buenos

Aires,

lor

_helping-

in

_{the technique}

adaptation,

Y

_{Yonenaga-Yassuda,}

Bioscience

Institute, USP,

Sdo

Paulo,

for assistance in the

analysis

of results, E A

_Greg6rio

and MH _Moreno, Electron

_{Microscopy Center, IB,}

NESP, Botucatu,

for utilization of the electron _microscope and CAPES for supporting the

project.

’

REFERENCES

Gillies

_CB,

Cowan SK

₍₁₉₈₅₎

The

_{pachytene synaptonemal complex complement}

of the

cat. Genetica

_67,

99-107

Greenbaum

_IF,

Hale

_DW,

Fuxa KP

₍₁₉₈₆₎

The mechanism of autosomal synapsis and the

substaging

of _zygonema and

_pachynema

from deer mouse _{spermatocytes.} Chromoso!rrca

93, 203-212

Howell

_WM,

Black DA

₍₁₉₈₀₎

Controlled silver

_staining

of nucleolus

organizer regions

with a _protective colloidal

developper:

a 1-step method.

Experientia

36, 1014-1015 5

Joseph AM, Chandley

AC

₍₁₉₈₄₎

The

_{morphological}

sequence of XY pairing in the

Norway

rat Rattus

norvegicus.

Chromosoma 89, 381-386

Moses MJ

_{( 1977)}

_{Synaptonemal complex karyotyping}

in _{spermatocytes} of Chinese hamster

(CricetuLus griseus).

II.

Morphology

of the XY _pair in

_spread

_{preparations.}

Chromo-soma

60,

127-137

Solari AJ

₍₁₉₇₀₎

The

_{spatial relationship}

of the X and Y chromosome

_during

meiotic

prophase

in mouse _{spermatocytes.} Chromosoma

29,

217-236

Solari AJ

_{( 1980)}

_{Synaptonemal complexes}

and associated structures in

_microspread

human