Search

Bone morphogenetic proteins (BMPs) were first studied as growth factors or morphogens of the transforming growth factor-beta superfamily. These growth molecules, originally associated with bone and cartilage development, are now known to play an important role in morphogenesis and homeostasis in many other tissues. More recently, significant contributions from BMPs, their receptors, and interacting molecules have been linked to carcinogenesis and tumor progression. On the other hand, BMPs can sometimes function as a tumor suppressor. Our report highlights these new roles in the pathogenesis of cancer that may suggest novel targets for therapeutic intervention., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

Although ideas on the stem cell origins of cancer date more than one hundred years, critical evidence to support these theories is largely lacking. Our objective here is to outline our historical perspective on keratinocyte stem cells in the cutaneous epithelium and to summarize specific evidence suggesting that epithelial stem cells may contribute to chemically induced skin cancer. We note that, while strong evidence does support this hypothesis, experiments in progress may provide direct visualization of tumors derived from hair follicle stem cells.

Primary adult mouse keratinocytes are harvested from the dorsal section of 6- to 8-wk-old mice. Euthanized mice are clipped and sterilized with serial washes in provodine iodine and ethanol solutions. The skin of the mice is removed and treated with trypsin to detach the dermis from the epidermis. Cells harvested from this proven method can be used for molecular biology, biochemistry, or a variety of cell culture techniques, including the clonogenic cell assay presented here.

To identify slowly cycling (label-retaining) keratinocytes in the cutaneous epithelium of mice, newborn female pups were injected with [3H]-thymidine twice daily for 3 d beginning the third day after birth. At 8-10 wk of age, skin from the dorsal side of the mice was removed and fixed. The skin was processed for paraffin embedding, and serial sections were prepared. Dewaxed and ethanol-treated slides were dried and dipped into autoradiographic emulsion and allowed to dry in light tight box for 4 wk at 4 degrees C. After fixation with photographic fixer, the slides were washed, lightly stained, and viewed with a light microscope to observe and quantify cells that retained the labeling. Label-retaining cells were identified by the black silver grains over their nuclei.

The hair follicle bulge possesses putative epithelial stem cells. Characterization of these cells has been hampered by the inability to target bulge cells genetically. Here, we use a Keratin1-15 (Krt1-15, also known as K15) promoter to target mouse bulge cells with an inducible Cre recombinase construct or with the gene encoding enhanced green fluorescent protein (EGFP), which allow for lineage analysis and for isolation of the cells. We show that bulge cells in adult mice generate all epithelial cell types within the intact follicle and hair during normal hair follicle cycling. After isolation, adult Krt1-15-EGFP-positive cells reconstituted all components of the cutaneous epithelium and had a higher proliferative potential than Krt1-15-EGFP-negative cells. Genetic profiling of hair follicle stem cells revealed several known and unknown receptors and signaling pathways important for maintaining the stem cell phenotype. Ultimately, these findings provide potential targets for the treatment of hair loss and other disorders of skin and hair.

The herbivorous insects of tropical forests constitute some of the most diverse communities of living organisms. For this reason it has been difficult to discover the degree to which these communities are structured, and by what processes. Interspecific competition for resources does occur, but its contemporary importance is limited because most pairs of potentially competing insects feed on different host plants. An alternative way in which species can interact is through shared natural enemies, a process called apparent competition. Despite extensive theoretical discussion there are few field demonstrations of apparent competition, and none in hyper-diverse tropical communities. Here, we experimentally removed two species of herbivore from a community of leaf-mining insects in a tropical forest. We predicted that other species that share natural enemies with the two removed species would experience lower parasitism and have higher population densities in treatment compared with control sites. In both cases (on removal of a dipteran and a coleopteran leaf-miner species) we found significantly lower parasitism, and in one case (removal of the dipteran) we found significantly higher abundance a year after the manipulation. Our results suggest that apparent competition may be important in structuring tropical insect communities.