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.

Síndrome de Turner 45,XO asociado con una inversión pericéntrica del cromosoma 13 / Turner's syndrome 45, XO associated with a pericentric inversion of chromosome 13

El propósito del presente trabajo es el de describir a una paciente con manifestaciones clínicas del síndrome de Turner, quien al realizarle los estudios cromosómicos en cultivo de linfocitos de sangre periférica, y con técnicas de bandas G, mostró un complemento cromosómico de 45, XO y además una inversión pericéntrica del cromosoma 13 con sus puntos de ruptura en las bandas pll y ql4. Los padres y el hermano de la propósita presentaron un cariotipo normal. Se discuten los mecanismos probables de origen de ambas anomalías y los pocos casos reportados en la literatura

Replicative activity of X-chromosome and autosomes of Drosophila melanogaster in autosomal hyperploids and the problem of dosage compensation.

Replicative behaviour of two hyperploid autosomal arms (2L and 3L) of D. melanogaster has been analysed by 3H-thymidine autoradiography. Results reveal that hyperploid autosomal arms (2L-trisomy or 3L-trisomy) replicate synchronously with other disomic non-homologous chromosome arms i.e. there is no asynchrony in the initial mid or late phase of replication patterns between the trisomic 2L or trisomic 3L and disomic arms, suggesting that the extra dose of an autosomal arm can not alter the inherent pattern of replication of that arm. Results further reveal that 2L-trisomy or 3L-trisomy does not impart any influence on X-chromosomal replication in either sex. It is suggested from these results that change in the genomic dose of autosome does not play any role in modulating the replicative organization of the autosomes, 2L and 3L. Thus, although a regulatory mechanism of autosomal dosage compensation does exist for Drosophila, the hierarchy of genetic programming of regulation for X-chromosomal and autosomal dosage compensation might be different. Neither hypertranscriptive activity nor faster replication pattern of the male X-chromosome is influenced by 2L- or 3L-trisomy.

Distrofia muscular progresiva / Progressive muscular distrophy

El objeto de este articulo es informar el caso de un nino de 2 anos de edad, quien presento en forma precoz a los 8 meses, una disminucion de la fuerza y una pseudo hipertrofia muscular, que condiciono al ano de edad una marcha de "pato" muy caracteristica y sintomatologica que fue incrementandose paulatinamente. Los estudios, diagnosticos comprendieron: electromiografia, en la que se encontro alteraciones electricas de patrones miopaticos, en sangre aumento de enzimas sericas (TGO, TGP, CPK). Todos estos cambios han sido reportados en la literatura extranjera, llamando la atencion de este caso la precocidad de su presentacion (8 meses). Esta patologia es una entidad rara, pero la mas frecuente dentro del grupo de enfermedades musculares progresivas, de etiologia familiar con herencia recesiva ligada al cromosoma X en un 70 // y en un 30 // de etiologia desconocida.