74s Genet Sel Evol (1991) 23, suppl 1, 74s-77s Elsevier/INRA

Mitotic and meiotic studies in a bull carrying the 1/29 and 9/23 Robertsonian  translocations

A Bouvet', EP Cribiul, V Durand', HM Berland2, R Darré2

Institut National de la Recherche Agronomique, Laboratoire de Cytogénétique, Centres de Recherches de Jouy-en-Josas, 78350 Jouy-en-Josas;

2 Ecole Nationale VŽtŽrinaire de Toulouse, Laboratoire de Cytogénétique, 23, chemin des Capelles, 31076 Toulouse Cedex, France

(Proceedings of the 9th European Colloquium on Cytogenetics of Domestic Animals; Toulouse-Auzeville, 10-13 July 1990)

bull / Robertsonian translocations / mitosis / meiosis

Robertsonian translocations are the most commonly reported chromosome anomalies in cattle. The most widely spread is the 1/29 translocation reported at high frequencies in numerous breeds worldwide. In contraste the other Robertsonian translocations have been reported only as sporadic cases (Berland et al, 1988).

Recently, a Blonde dAquitaine bull was detected as a heterozygous carrier of two different Robertsonian translocations and the chromosomes involved were identified using R-, G- and C-banding techniques (Cribiu et al, 1989).

Synaptonemal complex behavior was also analyzed for the same animal (Bouvet and Cribiu, 1990). In the present report, banding results and kinetochore appearance in both trivalents are compared.

The karyotype of this bull included 58 chromosomes: the X and Y chromosomes, 54 acrocentric and two submetacentric chromosomes with different lengths and centromeric indices. The G- and R-bands, according to the Reading and Jouy-en-Josas conferences (Ford et al, 1980; Di Berardino et al, 1990), showed that chromosome pairs 1 and 29 and pairs 9 and 23, respectively, were involved in the two translocations. The C-banding technique revealed the presence of two constitutive heterochromatin blocks in the pericentromeric region of the 9/23 translocated chromosome and only one block on the long arms near the centromre of the 1/29 translocated chromosome (fig 1).

In surface-spread spermatocytes of the 1/29, 9/23 translocations-carrier bull, two autosomal synaptonemal complexes with submetacentric kinetochores were noted, whereas the other autosomal complexes had terminally located kinetochores and the X-Y bivalent was easily identifiable. The trivalents appeared to show complete synapsis and to have a cis-configuration. The average arm ratios for the 1/29 and 9/23 trivalents were 2.71 ± 0.53 and 1.54 ± 0.27, respectively.

The 9/23 trivalent appeared to have a more separated kinetochore area than the 1/29 trivalent in most of the cells examined (fig 2). The two trivalent figures remained independent and did not associate with the sex vesicle.

The 9/23 translocation is the third Robertsonian translocation reported in the Blonde d'Aquitaine breed (Berland et al, 1988).

The C-banding method revealed a basic diffŽrence between the 1/29 and 9/23 translocations. One block of juxtacentromeric constitutive heterochromatin appears on the long arm of the 1/29 translocation, whereas two blocks are present on the 9/23 translocation, as reported for the 21/27 translocation by Berland et al (1988). The presence of one or two blocks would suggest different chromosome rearrangement formation mechanisms. In the first case, one of the chromosomal breakpoints involves the short arms of one chromosome and the other is on the long arms of the second  chromosome near the centromeric region. In the second case, the breakpoints involve only the short arms of both chromosomes.

The difference in the separation of the kinetochore area between these two bovine Robertsonian translocations seems to confirm the presence of one or two heterochromatin blocks noted by C-banding in mitotic spreads. A similar misalignment of kinetochores after synaptic readjustment has previously been reported in the red kangaroo to be due to the presence of an extra C-band in one homologue of a submetacentric autosomal chromosome pair (Sharp, 1986).

Since the bebavior of both trivalents is identical during the meiotic prophase, size diffŽrence between the chromosomes involved and the presence of one or two blocks of pericentromeric heterochromatin do not seem to alter the meiotic process.

REFERENCES

Berland HM, Sharma AI Cribiu EP, Darré R, Boscher J, Popescu CP (1988) A new case of Robertsonian translocation in cattle. J Hered 79, 33-36

Bouvet A, Cribiu EP (1990) Analysis of synaptonemal complexes behaviour in a bull carrying the 1/29 and 9/23 Robertsonian translocations. Reprod Domest Anim 25, 215- 219

Cribiu EP, Matejka M, DarrŽ R, Durand V, Berland HM, Bouvet A (1989) Identification of chromosomes involved in a Robertsonian translocation in cattle Genet Sel Evol 21, 555-560

Di Berardino D, Hayes H, Fries H, Long S (1990) Proceedings of the Second International Conference for the Standardization of Domestic Animal Karyotypes. Jouy-en-Josas, France, 22-26 May 1989. Cytogenet Cell Genet 53, 65-79

Ford CE, Pollock DL, Gustavsson 1 (1980) Proceedings of the First International Confer ence for the Standardization of Banded Karyotypes of Domestic Animals, Reading, 2-6

August 1976. Hereditas 92, 145-162 Sharp PJ (1986) Synaptic adjustment at a C-band heterozygosity. Cytogenet Cell Genet 41, 56-57


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