Synaptonemal complexes and XY behavior in two species of argentinian armadillos: Chaetophractus villosus and Dasypus hybridus (Xenarthra, Dasypodidae)

Spermatocytes from the two armadillo species, C. villosus and D. hybridus were studied in microspreads for synaptonemal complexes (SCs) and in thin sections for electron microscopy (EM). The complete se karyotype generally agrees with previous reports on mitotic chromosomes, except for the sex chromosomes. The X chromosome is submetacentric in both species and the Y is the shortest one in C. villosus and the second shortest in D. hybridus, and an extremely acrocentric one. A SC is formed along the total length of the Y chromosome, and this SC persists along all the pachytene substages. A single recombi-nation nodule (RN) is located in the region of the se nearest to the attachment to the nuclear envelope. The lateral element (LE) of the X axis in the SC shows a wavy aspect in most of the se length distant from the nuclear envelope. Nucleoli are attached to acrocentric or submetacentric bivalents, are visibly double in some cells , and in thin sections show an elaborate nucleolonema. Some differences in the XY are species-specific, as the higher degree of tangling and stronger heteropycnosis in D. hybridus. The effective, single crossover of the XY pair is highly localized, despite the permanence of a long tract of SC

Changes in crossover distribution along a quadrivalent in aman carrier of a reciprocal translocation t(11; 14)

A testicu1ar biopsy from an infertile man carrying a heterozygous chromosome translocation t(ll; 14) was studied with synaptonemal complex analysis and immunolocalization of the protein MLH 1 for crossover detection. A full blockage of spermatogenesis at the spermatocyte stage was related to the presence of the translocation quadrivalents at pachytene. Only 2% of the quadrivalents showed full synapsis. Most of the spermatocytes showed asynaptic free ends that frequently mingled with the XY pair. The average number of crossovers per cell was diminished from a mean of 52.7 in controls to a mean of 48 in the patient. The difference between the number of crossovers in the quadrivalent and the normal bivalents was highly significant. The distribution of crossovers over the segment of the quadrivalent corresponding to bivalent #14 was also very different from that ofthe control. It is concluded that in this translocation, the pattern of crossovers is changed, mainly due to a synaptic hindrance in the quadrivalent, and that the spermatogenesis arrest is mainly due to the quadrivalents that interact with the XY pair

A unique mechanism of nuclear division in Giardia lamblia involves components of the ventral disk and the nuclear envelope

The fine structure of the binucleate, parasitic protist Giardia lamblia during interphase and divisional stages was studied by serial thin sectioning and three-dimensional reconstructions. The earlier sign of nuclear division is the development of a few peripheral areas of densely packed chromatin directly attached to the inner nuclear envelope. An intracytoplasmic sheet of ventral disk components grows from the cell periphery towards one of the nuclei, apparently constricting this nucleus, which becomes located at a ventral bulge. After the basal bodies become duplicated, a full nuclear division occurs in trophozoites, giving two pairs of parent-daughter nuclei. This full division occurs in a dorsal-ventral direction, with the resulting nuclear pairs located at the sides of the two sets of basal bodies. A new ventral disk is formed from the disk-derived sheets in the cell harboring the four nuclei. Cytokinesis is polymorphic, but at early stages is dorsal-to-dorsal. Encysting trophozoites show the development of Golgi cisternae stacks and dense, specific secretory granules. 3-D reconstructions show that cysts contain a single pair of incompletely strangled nuclei. The dividing Giardia lacks a typical, microtubular spindle either inside or outside the nuclei. The nuclear envelope seems to be the only structure involved in the final division of the parent-daughter nuclei.

The behavior of sex chromosomes in two human X-autosome translocations: failure of extensive X-inactivation spreading

Two patients, one adult male and one infant girl, bearing different X-autosome translocations, were studied with cytogenetical, ultrastructural and chromosome-painting techniques. The adult male, is a carrier of a reciprocal, balanced translocation involving the X and #2 chromosomes: 46,Y,t(X;2) (q13;p21). This man showed infertility with spermatogenesis arrest at the spermatocyte stage. Synaptonemal complex analysis at pachytene showed the quadrivalent structure and the putative breakage points. Sex-chromatin condensation did not spread towards the autosomal regions of the quadrivalent. The female infant showed diminished body growth and multiple somatic anomalies. She is a 45,Xp-,t(X;21)(p11;p13) carrier, an unbalanced translocation involving chromosomes X and #21, which leads to a monosomy of almost all Xp. The translocated #21 is practically complete, and its centromere is the active one in the rearranged product. The analysis of interphase nuclei with the X-centromere probe shows that the Xq region of the rearranged chromosome is the late -replicating and inactive element. However, X-inactivation does not spread to the attached #21, as shown by the R-banding pattern. Thus, both in the male adult and in the female infant there is a barrier to the spreading effect of X-chromosome inactivation, which is probably due to different mechanisms.

First demonstration of the substructure of recombination nodules

Recombination nodules are submicroscopic structures that are found in all the sexually reproducing, eukaryotic organisms during the pachytene stage of meiotic prophase I. Despite many reports on their number and location, no definite substructure was previously reported in these nodules. The present observations on spread oocytes and spermatocytes of the pigeon, using an improved technique for protein preservation, shown the presence of particulate subunits or "recombinomeres" in late recombination nodules, besides an interparticle matrix. The number of subunits per each nodule ranges from 1 to 5, and this number increases with the advancement of pachytene substages. These subunits are present in recombination nodules of all the other avian species previously studied, and they may be present in other organisms as well. It is suggested that the particulate substructure of recombination nodules mirrors the multiplicity of multienzymatic complexes that are needed for the ordered series of reactions that occur at the molecular level in the sites of meiotic recombination

Hemangioma de pared torácica / Hemangioma of the chest wall

Se presenta un caso de Hemangioma de la pared torácica con crecimiento endotorácico que fue diagnosticado por toracotomía ya que debuta con derrames pleurales inespecíficos no permitiendo llegar a un diagnóstico prequirúrgico. Se hace una breve reseña histórica y una somera clasificación histopatológica dándose pautas diagnósticas y terapéuticas.Se hace referencia a la rareza de localización y forma de crecimiento para tenerlo en cuenta en el momento de hacer diagnósticos diferenciales

Characterization of Trypanosoma cruzi populations by several molecular markers supports a clonal mode of reproduction

Chilean T. cruzi populations from different endemic areas and transmission cycles were characterized at several biochemical levels, to mention: hybridization with kinetoplast DNA probes, molecular karyotype, isoenzyme studies and kinetoplast DNA restriction fragment length polymorphism. Furthermore, an immunological approach with immune sera from Balb/c infected mice with different T. cruzi populations was used to differentiate among parasite types by the in vitro complement-mediated lysis assay. Parasite grouping by the above described methods allows to classify T. cruzi populations on a very defined number, suggesting that they have a clonal structure

Synaptonemal complex karyotyping in an oligospermic patient with heterochromatin duplication in chromosome n§ 9

Se ha realizado el análisis de complejos sinaptonépticos en espermatocitos de un paciente con oligospermia severa de etiologéa desconocida y portador de un polimorfismo de la heterocromatina paracentrométrica del cromosoma 9. La espermatogénesis del paciente está disminuida en las espermátidas, que presenta anormalidades ultraestructurales en especial en la condensación de la cromatina. En los espermatocitos en paquitene temprano hay un lazo muy visible y asimétrico en el bivalente 9, que en paquitene tardío desaparece frecuentemente, probablemente por un proceso de reajuste sináptico. El lazo es debido a que uno de los elementos es en promedio 7.02% mayor que el otro y que la media de los elementos 9 normales. Esta diferencia indica la presencia de un reordenamiento cromosómico en estado heterocigótico en la región paracentromérica del brazo largo del par 9, que corresponde probablemente a una duplicación en tánden de alrededor del 50% de la zona heterocromática normal. La extensión del lazo sugiere que puede sobrepasar el centrómero y ocupar un segmento del brazo corto. Si bien no es posible asegurar la existencia de una asociación causal entre la anomalía y la hipoespermatogénesis, esta observación se suma a otras sobre inversiones pericéntricas con lazos asinápticos en paquitene, en las cuales hay severa oligospermia o azoospermia. Sobre esta base se sugiere un estudio análogo en otros pacientes portadores de polimorfismos del 9

Mutante de Streptococcus lactis con resistencia a bacteriófagos aislados en Argentina y Estados Unidos de América / A mutant of Streptococcus lactis with resistance to bacteriophages isolated in Argentina and the United States of America

Streptococcuslactis y S. cremoris, bacterias lácticas utilizadas para la producción de quesos, pueden reesultar infectadas por bacteriófago específicos, lo que ocasiona alteraciones en la calidad, disminución de la productividad económicas significativas. Los métodos de desinfección y control más usuales no siempre resultan en una completa protección contra la proliferación de los fagos, por los que se ha recurrido al empleo de cepas resistentes a los mismos. En el presente trabajo se ha empleado un método simple y directo para obtener mutantes espontáneas de S. lactis con resistencia a fagos. La mutante S.lacts C26 obtenida a partir de la cepa S. lactis C2 sensible a fagos exhibe propiedades bioquímicas y microbiológicas similares a las de la cepa original C2, diferenciándose de ella por una clara resistencia al fago St15, de morfología alargada, utilizado para la selección. Las curvas de la cinética de crecimiento de la mutante en ausencia y en presencia del fago resultaron semejantes. La cepa C26 fue controlada con otros dos fagos aislados en Argentina y con seis fagos de dos tipos morfológicos, aislados en la Universidad de Cornell en EE.UU. La cepa C26 que fuera aislada como mutante resistente al fafo St15, resultó también resistente a todos ellos. Por otra parte, ha sido de interés verficar que los fagos no siempre observan una especificidad estricta con respecto a la especie de la célula huésped. El fago D59-1, aislado utilizando una cepa S. cremoris, también provoca una lisis significativa en la cepa S. lactis C2, suiriendo que ambas poseen sitios receptores semejantes. La mutante C26 fue empleada con éxito en Buenos Aires, en la planta elaborada de quesos donde fuera aislado el fago St15, lo que alienta la posibilidad de emplear esta metodología en el desarrollo de fermentos lácticos