Decay of homologous chromosome pairs and discovery of males in the thelytokous fungus-growing ant Mycocepurus smithii.

The prevalent mode of reproduction among ants is arrhenotokous parthenogenesis where unfertilized eggs give rise to haploid males and fertilized eggs develop into diploid females. Some ant species are capable of thelytokous parthenogenesis, a type of asexual reproduction where females develop from unfertilized diploid eggs. Thelytoky is well-documented in more than 20 ant species. Cytogenetic data are available for six species demonstrating that some thelytokous ant species are capable of producing males occasionally as well as maintaining their chromosome numbers and proper chromosome pairings. Mycocepurus smithii is a thelytokous fungus-growing ant species that inhabits large parts of Central and South America. Cytogenetic data are unavailable for M. smithii and male individuals were never documented for this species, although the presence of males is expected because genetic recombination was observed in a few sexually reproducing populations in Brazil and haploid sperm was documented from the spermathecae of M. smithii queens. This study aims at comparatively studying asexual and sexual populations of M. smithii using classical and molecular cytogenetic methods to test whether karyotype configuration is modified according to the mode of reproduction in M. smithii. Moreover, we report the discovery of M. smithii males from a sexually reproducing population in the Brazilian state Pará, diagnose the male of M. smithii, and morphologically characterize their spermatozoa. Karyotypic variation was observed within the asexual population (2n = 9, 10, or 11), whereas the chromosome number was fixed in the sexual population (2n = 14, n = 7). Identical karyotypes were maintained within individual M. smithii colonies and karyotype variation was only observed between colonies. In asexual individuals, the karyomorphs showed a decay of homologous chromosome pairs, especially in individuals with the karyomorph 2n = 11, which is potentially caused by relaxed natural selection on proper chromosome pairing. In contrast, females in the sexual population showed proper homologous chromosome pairings. In individuals of both asexual and sexual populations, we find that heterochromatin was localized in centromeric regions and on the short arms of the chromosomes, GC-rich regions were associated with heterochromatic regions, and 18S rDNA genes were located on the largest chromosome pair. This comparative cytogenetic analysis contributes to our understanding about the cytological mechanisms associated with thelytokous parthenogenesis in ants and suggests the decay of chromosome structure in the absence of meiosis and genetic recombination.

Attenuation of virulence in an apicomplexan hemoparasite results in reduced genome diversity at the population level.

BACKGROUND: Virulence acquisition and loss is a dynamic adaptation of pathogens to thrive in changing milieus. We investigated the mechanisms of virulence loss at the whole genome level using Babesia bovis as a model apicomplexan in which genetically related attenuated parasites can be reliably derived from virulent parental strains in the natural host. We expected virulence loss to be accompanied by consistent changes at the gene level, and that such changes would be shared among attenuated parasites of diverse geographic and genetic background. RESULTS: Surprisingly, while single nucleotide polymorphisms in 14 genes distinguished all attenuated parasites from their virulent parental strains, all non-synonymous changes resulted in no deleterious amino acid modification that could consistently be associated with attenuation (or virulence) in this hemoparasite. Interestingly, however, attenuation significantly reduced the overall population's genome diversity with 81% of base pairs shared among attenuated strains, compared to only 60% of base pairs common among virulent parental parasites. There were significantly fewer genes that were unique to their geographical origins among the attenuated parasites, resulting in a simplified population structure among the attenuated strains. CONCLUSIONS: This simplified structure includes reduced diversity of the variant erythrocyte surface 1 (ves) multigene family repertoire among attenuated parasites when compared to virulent parental strains, possibly suggesting that overall variance in large protein families such as Variant Erythrocyte Surface Antigens has a critical role in expression of the virulence phenotype. In addition, the results suggest that virulence (or attenuation) mechanisms may not be shared among all populations of parasites at the gene level, but instead may reflect expansion or contraction of the population structure in response to shifting milieus.

Atherosclerotic plaque rupture and intraplaque hemorrhage do not correlate with symptoms in carotid artery stenosis.

OBJECTIVE: Previously we failed to demonstrate a correlation between plaque type and symptoms in 165 carotid endarterectomy specimens. The purpose of this study was to analyze the relation between the anatomy of the carotid plaques and the presence of symptoms in 281 carotid endarterectomy specimens. METHODS: The patients were 213 men (mean age, 68 years) and 68 women (mean age, 68.7 years), with symptomatic disease (n = 133) or asymptomatic disease (n = 148). Specimens were processed for histologic analysis and immunohistochemistry. RESULTS: Plaques were categorized as complicated or noncomplicated, and ruptured or nonruptured. Risk factors could not be correlated with any pathologic or immunohistochemical findings or between plaque type and clinical symptoms. CONCLUSIONS: Almost 70% of plaque specimens demonstrated thrombus, intraplaque hemorrhage, or both. Thrombosis was observed in one fourth of specimens, and intraplaque hemorrhage in almost two thirds of specimens. Sixty four percent of plaques demonstrated neovascularization. It was not possible to demonstrate that complicated plaques (plaque rupture, thrombosis, intraplaque hemorrhage) are associated with symptoms, and it appears that such plaques may occur at any time, irrespective of symptoms.

Endarterectomía carotídea / Carotid endarterectomy

Objetivo: La endarterectomía carotídea fue introducida en los años 50 como procedimiento necesario para la prevención de la enfermedad carotídea. Material y métodos: En el Instituto Cardiovascular de Buenos Aires entre octubre de 1993 y mayo de 1995 fueron operados a 130 endarterectomías carotídeas. Ochenta y ocho eran hombres, con una edad promedio de 65 años. Como factores de riesgo el 77,6 por ciento era hipertenso, el 16,8 por ciento era diabético, el 63 por ciento dislipémico y el 61 por ciento tabaquista. El 18,4 por ciento había tenido un IAM previamente, el 23,6 por ciento angina crónica estable y el 24 por ciento presentaba claudicación en miembros inferiores. Del total de pacientes operados el 38 por ciento había presentado síntomas neurológicos hemisféricos: AIT 25 por ciento, amaurosis fugax 8,8 por ciento o stroke 3,2 por ciento. La operación realizada fue la endarterectomía carotídea común e interna luego de realizar arteriotomía longitudinal amplia y endarterectomía carotídea externa por eversión. Si la endarterectomía de la externa no era considerada satisfactoria también se realizaba arteriotomía de la misma. En todos los casos se utilizó shunt de Javid. Se fijó la placa distal y se realizó angioplastía con parche en la mayoría de los casos. Se realizó estudio anatomopatológico de 88 de dichas piezas de endarterectomía. Resultados: De las 130 endarterectomías realizadas la incidencia de déficit neurológico central (transitorio o definitivo) homolateral fue de 2,3 por ciento y contralateral 0,7 por ciento. La mortalidad perioperatoria fue 1,5 por ciento y la morbimortalidad global fue del 4,5 por ciento. Conclusiones: La endarterectomía carotídea para estenosis carotídeas mayores al 60 por ciento es el tratamiento de elección para prevenir eventos neurológicos mayores

Ateroembolismo / Atheromatous embolism

Objetivo: La microembolia masiva es una patología difícil de diagnosticar y tratar, grave, que con frecuencia conduce a la muerte de los pacientes. Material y métodos: Entre enero de 1993 y mayo de 1995 ingresaron 11 pacientes con diagnóstico de ateroembolismo. Diez eran hombres con edad promedio de 72 años, evaluados mediante TC y angiografía digital. Resultados: El tratamiento consistió en cirugía convencional en todos los casos, excepto en uno en el que se realizó un procedimiento endovascular. La mortalidad fue de 45 por ciento. Se hace especial hincapié en la administración de prostaglandina intra-arterial para el tratamiento de las lesiones isquémicas distales. Conclusiones: El ateroembolismo puede provenir de trombos originados en úlceras ateromatosas o de desprendimientos de fragmentos de placas de ateroma. Está compuesto por pequeños acúmulos de fibrina, plaquetas, células sanguíneas y cristales de colesterol. Estos pacientes presentan en general aortas ulceradas, friables, desflecadas e irregulares, aneurismas aórtico o ilíacos y con menor frecuencia poplíteos. Cuando comprometen a los parénquimas viscerales tienen peor pronóstico. Se relata la sistemática de diagnóstico y tratamiento quirúrgico, el tratamiento de exclusión de la circulación de la fuente embolígena sobre la aorta y el incremento de esta patología por procedimientos diagnósticos angiorradiológicos o anticoagulación sistémica