Synaptic configuration of quadrivalents and their association with the XY bivalent in spermatocytes of Robertsonian heterozygotes of Mus domesticus

BACKGROUND: The nuclear architecture of meiotic prophase spermatocytes is based on higher-order patterns of spatial associations among chromosomal domains and consequently is prone to modification by chromosomal rearrangements. We have shown that nuclear architecture is modified in spermatocytes of Robertsonian (Rb) homozygotes of Mus domesticus. In this study we analyse the synaptic configuration of the quadrivalents formed in the meiotic pro- phase of spermatocytes of mice double heterozygotes for the dependent Rb chromosomes: Rbs 11.16 and 16.17. RESULTS: Electron microscope spreads of 60 pachytene spermatocytes from four animals of Mus domesticus 2n = 38 were studied and their respective quadrivalents analysed in detail. Normal synaptonemal complex was found between arms 16 of the Rb metacentric chromosomes, telocentrics 11 and 17 and homologous arms of the Rb metacentric chromosomes. About 43% of the quadrivalents formed a synaptonemal complex between the heterologous short arms of chromosomes 11 and 17. This synaptonemal complex is bound to the nuclear envelope through a fourth synapsed telomere, thus dragging the entire quadrivalent to the nuclear envelope. About 57% of quadrivalents showed unsynapsed single axes in the short arms of the telocentric chromosomes. About 90% of these unsynapsed quadrivalents also showed a telomere-to-telomere association between one of the single axes of the telocentric chromosome 11 or 17 and the X chromosome single axis, which was otherwise normally paired with the Y chromosome. Nucleolar material was associated with two bivalents and with the quadrivalent. CONCLUSIONS: The spermatocytes of heterozygotes for dependent Rb chromosomes formed a quadrivalent where four chromosomes are synapsed together and bound to the nuclear envelope through four telomeres. The nuclear configuration is determined by the fourth shortest telomere, which drags the centromere regions and heterochromatin of all the chromosomes towards the nuclear envelope, favouring the reiterated encounter and eventual rearrangement between the heterologous chromosomes. The unsynapsed regions of quadrivalents are frequently bound to the single axis of the X chromosome, possibly perturbing chromatin condensation and gene expression.

Papel do cromossomo Y na diferenciaçäo gonadal / Y chromosome role in the gonadal differentiation

Os autores fazem uma revisao sobre a evoluçao dos conceitos de diferenciaçao gonadal, desde a descoberta dos cromossomos X e Y até a localizaçao da seqüência de bases, no braço curto do cromossomo Y, próximo à regiao pseudoautossômica, supostamente responsável pela diferenciaçao da gônada bipotencial a testículo. O assunto desperta grande interesse, pois nem todos os passos deste verdadeiro quebra-cabeças foram desvendados e a questao do virilismo XX ainda se acha aberta à pesquisa científica.

Use of y-chromosome-specific DNA probes to evaluate an XX male

The function of a Y human chromosomal DNA sequence was evaluated. The Y-5 probe was isolated from a flow-sorted chromosome library and detects Y-specific sequences. The Y-5 probe and other T-specific probes were used to analyze an XX male patient without ambiguous genitalia. DNA sequences from the short arm of the chromosome Y that were detected with pDP1007 and DP105 in the patient's genome explain the testis differentation observed in this case. Failure of the patient's DNA to hybridize to the Y-5 probe shows that the primitive gonads can differentiate into testes even in the absence of this chromosome region. In contrast, a gene controlling spermatogenesis may exist in this region because the patient azoospermic