Morphological, developmental and immunohistochemical observations on the opossum pituitary with emphasis on the pars intermedia

Independent genetic mechanisms mediate turgor generation and penetration peg formation during plant infection in the rice blast fungus

The first barrier to infection encountered by foliar pathogens is the host cuticle. To traverse this obstacle, many fungi produce specialized infection cells called appressoria. MST12 is essential for appressorium-mediated penetration and infectious growth by the rice pathogen Magnaporthe grisea. In this study, we have characterized in detail the penetration defects of an mst12 deletion mutant. Appressoria formed by the mst12 mutant developed normal turgor pressure and ultrastructure but failed to form penetration pegs either on cellophane membranes or on plant epidermal cells. Deletion and site-directed mutagenesis analyses indicated that both the homeodomain and zinc finger domains, but not the middle region, of MST12 are essential for appressorial penetration and plant infection. The mst12 mutant appeared to be defective in microtubule reorganization associated with penetration peg formation. In mature appressoria, the mutant lacked vertical microtubules observed in the wild type. The mst12 mutant also failed to elicit localized host defence responses, including papilla formation and autofluorescence. Our data indicate that generation of appressorium turgor pressure and formation of the penetration peg are two independent processes. MST12 may play important roles in regulating penetration peg formation and directing the physical forces exerted by the appressorium turgor in mature appressoria.

Brain growth and neocortical development in the opossum

General brain growth and differentiation of the neocortex have been studied in the marsupial, Didelphis virginiana from the 10.5 day embryo through adulthood. Didelphis is born after a short gestation period of about 12.5 days, at a time when the telencephalic wall consists only of two layers and is considered to be at an embryonic stage of development. The cortical plate does not appear until late in the first postnatal week, thus neocortical development is totally a postnatal phenomenon in Didelphis as has been shown in other marsupial species examined to date. The general pattern of development and the establishment of the six-layered adult neocortex in Didelphis is similar to that described in eutherian mammals. Signs of cortical lamination can be seen as early as postnatal day 35 and the cytoarchitecture of a typical mammalian neocortex is well defined by postnatal day 60 in Didelphis prior to the onset of weaning.

Posterior pituitary of the newborn marsupial possum, Trichosurus vulpecula

The fetal anterior pituitary-adrenal axis is thought to be involved in the initiation of birth in both eutherian and marsupial mammals. Little is known about the structure and function of the posterior pituitary at birth in the marsupial. Immunocytochemistry, high pressure liquid chromatography, and radioimmunoassay were used to identify vasopressin and mesotocin in the posterior pituitary of a newborn marsupial, the brushtail possum, Trichosurus vulpecula. The concentrations of vasopressin and mesotocin in the head of the newborn possum were 0.34 and 0.28 ng, respectively. The concentration of vasopressin was always greater than that of mesotocin, and the amounts of neuropeptides present in the head increased as the possum developed.