Stem cells are units of natural selection in a colonial ascidian

Stem cells are highly conserved biological units of development and regeneration. Here we formally demonstrate that stem cell lineages are also legitimate units of natural selection. In a colonial ascidian, Botryllus schlosseri, vascular fusion between genetically distinct individuals results in cellular parasitism of somatic tissues, gametes, or both. We show that genetic hierarchies of somatic and gametic parasitism following fusion can be replicated by transplanting cells between colonies. We prospectively isolate a population of multipotent, self-renewing stem cells that retain their competitive phenotype upon transplantation. Their single-cell contribution to either somatic or germline fates, but not to both, is consistent with separate lineages of somatic and germline stem cells or pluripotent stem cells that differentiate according to the niche in which they land. Since fusion is restricted to individuals that share a fusion/histocompatibility allele, these data suggest that histocompatibility genes in Botryllus evolved to protect the body from parasitic stem cells usurping asexual or sexual inheritance.     

Potent pyrimidinetrione-based inhibitors of MMP-13 with enhanced selectivity over MMP-14

Through the use of computational modeling, a series of pyrimidinetrione-based inhibitors of MMP-13 was designed based on a lead inhibitor identified through file screening. Incorporation of a biaryl ether moiety at the C-5 position of the pyrimidinetrione ring resulted in a dramatic enhancement of MMP-13 potency. Protein crystallography revealed that this moiety binds in the S(1)(') pocket of the enzyme. Optimization of the C-4 substituent of the terminal aromatic ring led to incorporation of selectivity versus MMP-14 (MT-1 MMP). Structure activity relationships of the biaryl ether substituent are presented as is pharmacokinetic data for a compound that meets our in vitro potency and selectivity goals.     

Carotid artery stenting: update

"Extracranial carotid artery stenosis is responsible for approximately 20-30% of ischemic strokes. Traditionally, carotid artery stenosis has been treated with carotid endarterectomy. However, the low periprocedural complication rate and the mid term durability of carotid artery stenting has made it a competitive alternative treatment strategy. This update reviews the technical aspects of carotid artery stenting, clinical data supporting carotid artery stenting-particularly in high risk patients, and the complications associated with carotid artery stenting."     

Rat epidermal keratinocytes as an organotypic model for examining the role of Cx43 and Cx26 in skin differentiation

In order to characterize connexin expression and regulation in the epidermis, we have characterized a rat epidermal keratinocyte (REK) cell line that is phenotypically similar to basal keratinocytes in that they have the ability to differentiate into organotypic epidermis consisting of a basal cell layer, 2-3 suprabasal cell layers, and a cornified layer. RT-PCR revealed that REK cells express mRNA for Cx26, Cx31, Cx31.1, Cx37, and Cx43, which mimics the reported connexin profile for rat tissue. In addition, we report the expression of Cx30, Cx30.3, Cx40, and Cx45 in rat keratinocytes, highlighting the complexity of the connexin complement in rat epidermis. Furthermore, 3-dimensional analysis of organotypic skin revealed that Cx26 and Cx43 are exquisitely regulated during the differentiation process. The life-cycle of these connexins including their expression, transport, assembly into gap junctions, internalization, and degradation are elegantly depicted in organotypic epidermis as keratinocytes proceed from differentiation to programmed cell death.     

Cyclodextrin-polyethylenimine conjugates for targeted in vitro gene delivery

Many human gene therapies will require cell-specific targeting. Though recombinant viruses are much more efficient than nonviral vectors, the latter, especially polymers, have the advantage of being targetable via conjugation of cell-specific ligands, including sugars, peptides, and antibodies, which can be covalently attached to the polymer using a variety of chemistries. Cyclodextrin, which forms inclusion complexes with small hydrophobic molecules, has been incorporated into a gene-delivery polymer and may provide a facile and versatile attachment site for targeting ligands. Polyethylenimine (PEI) was derivatized with beta-cyclodextrin on approximately 10% of the polymer's amines (termed CD-PEI). Human insulin was also derivatized with a hydrophobic palmitate group (pal-HI), which could anchor the protein to CD-PEI/DNA polyplexes. CD-PEI was essentially nontoxic to HEK293 cells at concentrations optimal for gene delivery and mediated nearly 4-fold higher gene expression than unmodified PEI, which is relatively toxic to these cells. More importantly, addition of the pal-HI to CD-PEI enhanced gene expression by more than an order of magnitude compared to unmodified PEI, either with or without the pal-HI. Because of the relative ease with which CD-binding moieties may be attached to various types of ligands, CD-PEI may be a generally useful material for testing novel cell-specific targeting compounds.     

Expression of estrogen receptor beta in prostate carcinoma cells inhibits invasion and proliferation and triggers apoptosis

The involvement of estrogen receptor beta (ERbeta) in prostate carcinogenesis has been hypothesized. Several reports have shown that ERbeta expression was decreased when prostate cells undergo neoplastic transformation, suggesting that it could play a tumor-suppressor role. By restoring ERbeta expression in prostatic carcinoma cells by adenoviral delivery, we aimed to test this hypothesis. We observed that ERbeta strongly inhibited the invasiveness and the growth of these cells. In addition, ERbeta cells were undergoing apoptosis, as shown by quantification of Bax, poly(ADP-ribose) polymerase and caspase-3 expression. Our data suggest that ERbeta acts as a tumor-suppressor by its anti-proliferative, anti-invasive and pro-apoptotic properties.     

Decreased levels of Cx43 gap junctions result in ameloblast dysregulation and enamel hypoplasia in Gja1Jrt/+ mice

Coordinated differentiation of the ameloblast cell layer is essential to enamel matrix protein deposition and subsequent mineralization. It has been hypothesized that this process is governed by Cx43‐based gap junctional intercellular communication as oculodentodigital dysplasia (ODDD) patients harboring autosomal‐dominant mutations in Cx43 exhibit enamel defects typically resulting in early adulthood tooth loss. To assess the role of Cx43 in tooth development we employ a mouse model of ODDD that harbors a G60S Cx43 mutant, Gja1^Jrt/+, and appears to exhibit tooth abnormalities that mimic the human disease. We found that total Cx43 plaques at all stages of ameloblast differentiation, as well as within the supporting cell layers, were greatly reduced in Gja1^Jrt/+ incisors compared to wild‐type littermate controls. To characterize the Gja1^Jrt/+ mouse tooth phenotype, mice were sacrificed prior to tooth eruption (postnatal day 7), weaning (postnatal day 21), and adulthood (2 months postnatal). A severely disorganized Gja1^Jrt/+ mouse ameloblast layer and abnormal accumulation of amelogenin were observed at stages when the cells were active in secretion and mineralization. Differences in enamel thickness became more apparent after tooth eruption and incisor exposure to the oral cavity suggesting that enamel integrity is compromised, leading to rapid erosion. Additional analysis of incisors from mutant mice revealed that they were longer with a thicker dentin layer than their wild‐type littermates, which may reflect a mechanical stress response to the depleted enamel layer. Together, these data show that reduced levels of Cx43 gap junctions result in ameloblast dysregulation, enamel hypoplasia, and secondary tissue responses. J. Cell. Physiol. 223:601–609, 2010. © 2010 Wiley‐Liss, Inc.     

Competitive intransitivity promotes species coexistence

Using a spatially explicit cellular automaton model with local competition, we investigate the potential for varied levels of competitive intransitivity (i.e., nonhierarchical competition) to promote species coexistence. As predicted, on average, increased levels of intransitivity result in more sustained coexistence within simulated communities, although the outcome of competition also becomes increasingly unpredictable. Interestingly, even a moderate degree of intransitivity within a community can promote coexistence, in terms of both the length of time until the first competitive exclusion and the number of species remaining in the community after 500 simulated generations. These results suggest that modest levels of intransitivity in nature, such as those that are thought to be characteristic of plant communities, can contribute to coexistence and, therefore, community-scale biodiversity. We explore a potential connection between competitive intransitivity and neutral theory, whereby competitive intransitivity may represent an important mechanism for "ecological equivalence."