A new Robertsonian translocation in Blonde d'Aquitaine cattle, rob(4;10)

The cytogenetic study of a population of Blonde d’Aquitaine cattle revealed the presence of a Robertsonian translocation. The chromosomes involved in this abnormality were determined using G (GTG), R (RBG) and C (CBG) banding techniques. The chromosomes in question were identified as chromosomes 4 and 10. The existence of 2 paternal half-sisters carrying the abnormality suggests that it originates from the sire.


INTRODUCTION
Robertsonian translocations are the most commonly reported chromosome anomalies in cattle; the most widespread is the 1;29 translocation detected for the first time by Gustavsson and Rockborn (1964), and reported later with high frequency in numerous breeds worldwide (Popescu, 1977;Popescu and Pech, 1991). The 1;29 translocation is widespread in the Blonde d'Aquitaine breed since the frequency of the heterozygous and homozygous carriers ranges from 14 to 24% (Queinnec et at, 1974;Cribiu, 1985;Frebling et at, 1987). In contrast, as in other breeds, other Robertsonian translocations have been reported only as sporadic cases (Berland et at, 1988;Cribiu et at, 1989). The present report describes a new Robertsonian translocation observed in Blonde d'Aquitaine cattle.

Animals
Karyotypes were prepared from one phenotypically normal Blonde d'Aquitaine cow carrying the new translocation (the proband), its mother and 3 half-sisters (1 maternal half-sister and 2 paternal half sisters), belonging to private farms near Toulouse, southwest France. The pedigree is shown in figure 1.

Methods
The karyotype of each cow was determined using whole blood cultures (Grouchy et al, 1964) and primary skin cell cultures (Chaffaux et al, 1986). The peripheral blood was cultured at 37°C for 72 h in Ham's F12 medium supplemented with 20% fetal bovine serum, 2 mM glutamine, 100 pg/ml streptomycin and concanavalin A (final concentration: 0.1 yg/1). Colcemid (final concentration: 0.03 mg/1) was added to the culture 60 min before harvesting. Tissue biopsies were performed under local anesthesia on the rump. Primary fibroblast cultures were initiated from skin fragments, disrupted and digested in a trypsin solution (2.5 g/1) and grown in a CO 2 incubator as monolayer cultures in Falcon dishes (75 cm 2 ) containing a medium similar to that previously described for lymphocyte cultures.
G-banding was achieved using a modification of the technique of Seabright (1971). The C-bands were obtained by the barium hydroxide/saline/Giemsa (BSG) technique (Summer, 1972). To induce R-banding, 5-bromo-2-deoxyuridine was added to the medium at a final concentration of 10 or 20 pg/ml. The cultures were incubated at 37°C until the number of mitotic round cells reached a maximum, about 8 to 9 h after BrdU addition (Hayes et al, 1991). In order to obtain RBGbands, the cells were treated according to the procedure described by Hayes et al (1991) and fluorochrome-photolysis-Giemsa (FPG) staining was performed as described by Viegas-P6quignot et al (1989).
The chromosomes were identified, paired and arranged according to the recommendations of the Reading Conference (1976) and the ISCNDA (1989).

RESULTS
In classically stained metaphases, the karyotypes of the cow and 1 paternal halfsister included 59 chromosomes: the 2 X chromosomes, 56 acrocentric and one large submetacentric chromosome. The G-and R-bands showed that chromosome pairs 4 and 10 are involved in the translocation (figs 2, 3). The C-banding technique revealed the presence of 2 constitutive heterochromatin blocks in the pericentromeric region of the 4;10 translocated chromosome (fig 4). Among the other 3 animals examined, the mother, 1 paternal half-sister and 1 maternal half-sister were normal with a diploid chromosome number (2n) of 60.

DISCUSSION AND CONCLUSION
This chromosome abnormality is the fourth Robertsonian translocation reported in the Blonde d'Aquitaine breed. The first translocation was the 1 ;29 translocation which is known to have a wide distribution among AI bulls (Queinnec et al, 1974) and heifers (Frebling et al, 1987). Chromosomes implicated in the second and third translocations were identified as the 21 and 27, and the 9 and 23, respectively (Berland et al, 1988, Cribiu et al, 1989). These 2 rob(21;27) and rob(9;23) have been observed only in one Blonde d'Aquitaine) bull and its progeny respectively.
Robertsonian translocations are the result of the fusion of 2 acrocentric chromosomes. Two types of Robertsonian translocations have been described in the Blond d'Aquitaine breed, depending on the presence of one block (1;29 translocation) and