We investigated spikelet development in four distantly related species of the grass tribe Andropogoneae to determine whether spikelet development and the formation of unisexual florets are uniform throughout the tribe. We studied development in Bothriochloa bladhii, Coelorachis aurita, Heteropogon contortus, and Hyparrhenia hirta, and compared these with Panicum, a member of the sister tribe Paniceae. Many aspects of spikelet development in the species we have studied correlate with what is already known for Tripsacum and maize (both Andropogoneae), despite variation in how unisexual florets are distributed on the plant. The formation of unisexual spikelets is also uniform. All florets initiate both pistil and stamen primordia. In florets destined to be male, cell death occurs in the subepidermal layers of the gynoecium after the formation of a gynoecial ridge. In florets destined to be female, there is no apparent cell death in the stamens, but growth ceases after anther formation. The similarity in spikelet development and the formation of unisexual florets point to a common genetic mechanism for sex determination throughout the Andropogoneae and possibly the entire Panicoideae. Use of a cell death pathway to cause gynoecial abortion may be the basis of one morphological character that defines the subfamily.

Phage display screening allows the study of functional protein–protein interactions at the cell surface, but investigating intracellular organelles remains a challenge. Here we introduce internalizing-phage libraries to identify clones that enter mammalian cells through a receptor-independent mechanism and target-specific organelles as a tool to select ligand peptides and identify their intracellular receptors. We demonstrate that penetratin, an antennapedia-derived peptide, can be displayed on the phage envelope and mediate receptor-independent uptake of internalizing phage into cells. We also show that an internalizing-phage construct displaying an established mitochondria-specific localization signal targets mitochondria, and that an internalizing-phage random peptide library selects for peptide motifs that localize to different intracellular compartments. As a proof-of-concept, we demonstrate that one such peptide, if chemically fused to penetratin, is internalized receptor-independently, localizes to mitochondria, and promotes cell death. This combinatorial platform technology has potential applications in cell biology and drug development.

To test the osmoregulatory rules of Schwann cell aldose reductase (AR) and myo-inositol, JS1 Schwann cells were grown under control and hyperosmotic conditions with and without excess glucose or galactose. JS1 cells cultured in control conditions possessed AR protein and activity that were not altered by the inclusion of 25 mM glucose or galactose. Following culture with 100 mM NaCl, there was a decline in cell number accompanied by an increase in AR activity, both of which were attenuated by the addition of 25 mM glucose or galactose. Sorbitol was not detected in JS1 Schwann cells following culture in control, glucose-supplemented, or hyperosmotic medium, and dulcitol accumulated only following culture with galactose. However, both polyols were dramatically increased in JS1 cells cultured in hyperosmotic medium supplemented with 25 mM glucose or galactose. In contrast, myo-inositol levels were elevated only during hyperosmotic exposure but decreased when glucose or galactose was also present. These data are consistent with the use of polyol formation by JS1 Schwann cells as a means of responding to osmotic stress.

The E6 oncoprotein of high-risk human papillomavirus type 16 (HPV16) interacts with several nuclear transcription factors and coactivators in addition to cytoplasmic proteins, suggesting that nuclear import of HPV16 E6 plays a role in the cellular transformation process. In this study we have investigated the nuclear import pathways of HPV16 E6 in digitonin-permeabilized HeLa cells. We found that HPV16 E6 interacted with the karyopherin (Kap) ␣2 adapter and could enter the nucleus via a classical Kap ␣2␤1-mediated pathway. Interestingly, HPV16 E6 also interacted, via its basic nuclear localization signal (NLS) located at the C terminus, with both Kap ␤1 and Kap ␤2 import receptors. Binding of RanGTP to these Kap ␤s inhibited their interaction with HPV16 E6 NLS. In agreement with these binding data, nuclear import of the HPV16 E6 oncoprotein in digitonin-permeabilized HeLa cells could be mediated by either Kap ␤1 or Kap ␤2. Nuclear import via these pathways required RanGDP and was independent of GTP hydrolysis by Ran. Significantly, an E6 R124G mutant had reduced nuclear import activity, and the E6 deletion mutant lacking 121 KKQR 124 was not imported into the nucleus. The data reveal that the HPV16 E6 oncoprotein interacts via its C-terminal NLS with several karyopherins and exploits these interactions to enter the nucleus of host cells via multiple pathways.Human papillomaviruses (HPVs) are icosahedral DNA tumor viruses that infect squamous epithelial cells of the skin or of the anogenital and oropharyngeal mucosa. About 85 distinct HPV genotypes have been identified and fully sequenced, and more than 120 types have been partially characterized. Mucosal HPVs have demonstrated various degrees of oncogenic potential, with some classified as high risk, such as types 16, 18, 31, and 45, and others as low risk, such as types 6 and 11 (60). High-risk HPVs are frequently detected in invasive cervical carcinomas, whereas the low-risk types are more often associated with benign exophytic condylomas. HPV infection is associated with more than 90% of all cervical cancers, which is the second leading cause of cancer death among women worldwide (60).Integration of the viral genome, resulting in deletion of several genes including E2 and maintenance of only the E6 and E7 genes, is a hallmark of malignant progression. Abrogation of E2 expression as a result of integration leads to uncontrolled expression of the E6 and E7 oncoproteins, which is crucial for the establishment and progression of the tumors. High-risk HPV E6 and E7 proteins cooperatively induce cellular immortalization and transformation (32,40). Studies with transgenic mice suggest that whereas E7 promotes the formation of benign tumors, E6 acts primarily to accelerate progression of these benign tumors to the malignant stage (52).HPV16 E6 is a basic protein of 151 amino acids that is able to form a complex with the p53 tumor suppressor protein targeting p53 degradation (47). The E6-AP ubiquitin ligase facilitates the formation of the E6-p53 complex and functions...