Transition to extrauterine life and the modeling of perinatal asphyxia in rats.

Generation of murine models for the study of birth-related pathologies has proven to be a complex and controversial problem. Differences in the relative timing of developmental events of both species have led some researchers to suggest that the rat is born comparatively less developed than the human. The solution proposed to this problem would consist in the delay of the experiments of perinatal asphyxia (PA), usually up to 7-10 days, allowing developmental levels to "equalize" with the human at birth. This solution generates a new set of problems. The developmental milestones in both species follow a divergent temporal pattern. Increasing the age of the rat not only can improve resemblance with humans but also will make the model miss a crucial set of milestones related to birth. During this process, there are specific mechanisms to protect the fetus from neuronal damage, especially those caused by asphyxia. These factors are not present in models where the asphyxia is delayed. In these models, there will be more false positives and more damage that would not be present in humans exposed to PA. This article is categorized under: Cancer > Stem Cells and Development Congenital Diseases > Environmental Factors Neurological Diseases > Environmental Factors.

Insertion sequences as variability generators in the Mycoplasma hyopneumoniae and M. synoviae genomes

We have analyzed the sequenced genomes of three strains of Mycoplasma hyopneumoniae and one strain of M. synoviae, and have found three and two different transposable element families, respectively in each species. In M. hyopneumoniae, the Insertion Sequences of the IS4 family is represented by ISMHp1, a putatively active element. The IS3 family is represented by several degenerated sequences. A third element called tMH was found, which shows some characteristics reminiscent of retrotransposons. In M. synoviae, three different possibly active IS4 elements are present (ISMHp1-like; ISMs1 and IS1634-like elements). The IS30 family is represented by the degenerated IS1630-like element. The IS1634-like element is shown to be involved in chromosomal rearrangements and horizontal gene transfer (HGT). The ISMHp1-like element is shown to relate to the HGT of a 25-kb region from M. gallisepticum to M. synoviae. The fractions of these genomes that correspond to mobile elements varied from 1.35 to 3.13 percent in M. hyopneumonia strains and was 2.08 percent in M. synoviae. Although these species possess reduced genomes, they maintain mobile elements, perhaps as a mechanism for genetic variability production.