Curvature-driven spatial patterns in growing 3D domains: A mechanochemical model for phyllotaxis.

Here we discuss the formation of phyllotactic patterns in the shoot apical meristem (SAM) of plants, where the spatial distribution of the phytohormone auxin determines phyllotaxis in a domain that is growing and changing in time. We assume that the concentration of auxin modifies the mechanical properties of the domain and that the mechanical stress field in the SAM orients the flux of auxin. To study this problem we propose a mechanism for pattern formation in growing domains with variable curvature. The dynamics of chemicals is modeled by a reaction-diffusion system that produces a three dimensional pattern of chemical concentrations that changes the stress field in the domain while growing. The growth process is modeled by a phase-field order parameter which determines the location of the boundaries of the domain. This field is coupled to the chemical concentration through a curvature term that affects the local mechanical stress in the domain. The local stress changes in turn modify the chemical patterns. Our model constitutes a useful and novel approach in theoretical biology, as many developmental processes in organisms seem to be affected by the changes of curvature, size, mechanical stress and other physical aspects. Several patterns seen in many plants are reproduced under certain conditions by our model.

Genetic background of people in the Dominican Republic with or without obese type 2 diabetes revealed by mitochondrial DNA polymorphism.

People in the Dominican Republic are considered to be genetically heterogeneous owing to the post-Colombian admixture of Native American, African, and European populations. To characterize their genetic background, nucleotide sequences of the D-loop region of human mitochondrial DNA (mtDNA) were examined in 33 healthy women and 50 gender-matched patients with obese type 2 diabetes (OD) from the Dominican Republic. Phylogenetic analysis of 198 mtDNA lineages including Native Americans, Africans, and Europeans enabled us to assess relative genetic contributions of the three ancestral fractions to the two groups in the Dominican Republic. In the OD group, the majority (64.0%) of the mtDNA lineages were from African ancestry, whereas the Native American fraction was predominant (51.5%) in the healthy group, with both showing smallest amounts (14.0% and 9.1%, respectively) of European contribution. This difference in maternal genetic background between the two groups was similarly demonstrated by phylogenetic analysis at the population level based on net nucleotide diversities between populations. These findings may imply ethnic-specific predisposition to OD, a possible association of an unidentified factor from African ancestry with OD in the Dominican Republic population.

Ileo biblial yeyunal

Al tiempo que revisamos las características clínico-quirúrgicas que envuelven a la patología biliodigestiva que describieron Batholuis en 1854 y Bouveret, presentamos un caso tratado en el Centro Médico de la Universidad Central del Este (UCE), dada la baja incidencia universal de la patología. Bajo el diagnóstico de oclusión intestinal aaltas se interviene de emergencia una paciente de 74 años de edad. En el transoperatorio se evidenció una fístula vesicoduodenal, espontánea; un cálculo biliar único de 3.5 cms. de diámetro, obstruía el lúmen yeyunal a unos 90 cms., aproximadamente, del ángulo de Treitz. Se practicó una yeyunolitotomía sub-obstrutiva y yeyunorrafía transversa en uno solo plano, dejándose intacta la fístula biliodigestiva por razones evidentes en el orden táctico