Gene expression profiling of the developing mouse kidney and embryo.

The metanephros is formed from the reciprocal inductive interaction of two precursor tissues, the metanephric mesenchyme (MM) and the ureteric bud (UB). The UB induces MM to condense and differentiate forming the glomerulus and renal tubules, whilst the MM induces the UB to differentiate into the collecting tubules of the mature nephron. Uninduced MM is considered the progenitor cell population of the developing metanephros because of its potential to differentiate into more renal cell types than the UB. Previous studies have identified the phenotype of renal precursor cells; however, expression of candidate marker genes have not been analysed in other tissues of the murine embryo. We have assayed up to 19 candidate genes in eight embryonic tissues at five gestation stages of the mouse embryo to identify markers definitively expressed by renal cells during metanephric induction and markers developmentally regulated during kidney maturation. We then analysed their expression in other developing tissues. Results show Dcn, Hoxc9, Mest, Wt1 and Ywhaq were expressed at moderate to high levels during the window of metanephric specification and early differentiation (E10.5-E12.5 dpc), and Hoxc9, Ren1 and Wt1 expression was characteristic of mature renal cells. We demonstrated Cd24a, Cdh11, Mest, Scd2 and Sim2 were regulated during brain development, and Scd2, Cd24a and Sip1 expression was enriched in developing liver. These markers may be useful negative markers of kidney development. Use of a combination of highly expressed and negative markers may aid in the identification and removal of non-renal cells from heterogeneous populations of differentiating stem cells.

Development and manufacture of an investigational human living dermal equivalent (ICX-SKN).

AIM: To design and manufacture an investigational living skin graft replacement (ICX-SKN) that is able to incorporate into the host, providing healing by primary intent without the need for a second intervention. MATERIALS & METHODS: The ICX-SKN skin graft replacement has been designed as an allogeneic dermal substitute comprising an extracellular matrix composed largely of human collagen and human dermal fibroblast cells (HDFs). ICX-SKN is first formed by casting a provisional matrix of fibrin, into which HDFs are seeded. Through a process of maturation, HDFs are induced to lay down collagen and other extracellular matrix materials and, as the construct matures, the original fibrin is largely replaced by collagen, which provides tensile strength and flexibility to the construct. In order to design a product and manufacturing system that lends itself to large-scale production the process was developed as a discontinuous process consisting of four stages: 1. batch casting and maturation of the initial construct (pSKN), 2. freeze-drying of pSKN to produce a second intermediate (dSKN), 3. sterilization by gamma-irradiation of dSKN to produce a third intermediate (sSKN), and finally, 4. repopulation of sSKN by fresh HDFs to produce the final product, ICX-SKN skin graft replacement. Preliminary characterization of ICX-SKN and its application in a preclinical model are described. RESULTS: The 7-week maturation period resulted in a construct (pSKN) with robust handling properties, which was composed mainly of human collagen I. Following development of a process for freeze-drying and subsequent sterilization, the matrix was successfully repopulated with fresh HDFs. In addition, it was demonstrated that human keratinocytes attached and differentiated on the matrix. Application of human keratinocytes to the repopulated constructs (ICX-SKN) resulted in expression of markers of basement membranes that was largely dependent on the presence of living HDFs on the constructs. ICX-SKN graft replacements applied to excision wounds in mice healed and were rapidly re-epithelialized. CONCLUSIONS: ICX-SKN has been developed as a platform product that can be used as a skin graft replacement and the process by which it is manufactured has been designed for the product to be available to the end-user off-the-shelf and for ease-of-use in practice.

Integration and persistence of an investigational human living skin equivalent (ICX-SKN) in human surgical wounds.

AIM: To present the first human clinical data on an investigational living skin graft replacement that is being designed for application where tissue has been lost through surgery, disease or trauma. MATERIALS & METHODS: The ICX-SKN skin graft replacement is composed of an autosynthesized human collagen-based extracellular matrix and human dermal fibroblasts. In a first study to examine integration and persistence, full-thickness excisional wounds were made in six healthy human female volunteers and the ICX-SKN skin graft replacement applied and dressed. The surgical wounds were examined for up to 28 days post-application and the graft excised from each volunteer. RESULTS: Pre-excision gross examination revealed that the ICX-SKN skin graft replacement had integrated well in each of the six wounds and that re-epithelialization had occurred in each case. Histological analysis revealed that the ICX-SKN skin graft replacement remained in place and had become vascularized and provided a continuous wound closure. No serious adverse events were reported and no gross scarring or wound contracture was evident in the healed wounds. CONCLUSION: This is the first report of preliminary evidence indicating the persistence of an autosynthesized, tissue-engineered, living human skin substitute in healed acute wounds in humans.

Colonic expression of leukotriene-pathway enzymes in inflammatory bowel diseases.

BACKGROUND: Leukotrienes derived from the 5-lipoxygenase pathway are proinflammatory lipid mediators that possibly play a role in inflammatory bowel diseases. The expression of 5-lipoxygenase pathway proteins has not previously been examined in colonic mucosa in inflammatory bowel disease. RESULTS: Quantitative immunohistochemical analyses showed that, compared to those of the control subjects (n = 9), colonic biopsies from patients with active inflammatory bowel disease (n = 17) had 3- to 7-fold higher mean counts of cells expressing 5-lipoxygenase (P = 0.03), 5-lipoxygenase-activating protein (P = 0.005), and the leukotriene A(4) hydrolase (P = 0.004), which make up the biosynthetic pathway of the potent neutrophil chemotaxin leukotriene B(4). Immunoexpression of the leukotriene C(4) synthase was unaltered (P > 0.2). The increased representation of leukotriene B(4)-pathway enzymes was associated with higher counts of neutrophils (P = 0.0001), macrophages (P = 0.03), eosinophils (P = 0.0004), CD8(+) T cells (P < 0.001), activated T cells (P < 0.05), and B cells (P < 0.05) but not of mast cells (P > 0.9). These eicosanoid and cellular changes were most marked in the subgroup of patients with ulcerative colitis (n = 9), and were absent in patients with quiescent disease (n = 6). The anomalies in the 5-lipoxygenase pathway were accompanied as expected by more cells immunostaining for cytokine-inducible COX-2 (P = 0.004, n = 17), but this study also revealed a greater number of cells expressing COX-1 in the samples from the patients in the ulcerative colitis subgroup (P = 0.03, n = 9). CONCLUSIONS: The 5-lipoxygenase data provide a cellular basis for increased tissue synthesis of the leukotriene B(4), as reflected in the colonic mucosa and rectal dialysates of patients with active inflammatory bowel disease, which contributes to neutrophil influx and colonic injury. The COX-1/COX-2 data highlight the ambiguous functional role of prostanoid pathways in inflammatory bowel diseases.

XRCC3 and Rad51 modulate replication fork progression on damaged vertebrate chromosomes.

The mechanisms by which the progression of eukaryotic replication forks is controlled after DNA damage are unclear. We have found that fork progression is slowed by cisplatin or UV treatment in intact vertebrate cells and in replication assays in vitro. Fork slowing is reduced or absent in irs1SF CHO cells and XRCC3(-/-) chicken DT40 cells, indicating that fork slowing is an active process that requires the homologous recombination protein XRCC3. The addition of purified human Rad51C-XRCC3 complex restores fork slowing in permeabilized XRCC3(-/-) cells. Moreover, the requirement for XRCC3 for fork slowing can be circumvented by addition of human Rad51. These data demonstrate that the recombination proteins XRCC3 and Rad51 cooperatively modulate the progression of replication forks on damaged vertebrate chromosomes.

Reprogramming in inter-species embryonal carcinoma-somatic cell hybrids induces expression of pluripotency and differentiation markers.

Somatic cell reprogramming holds great promise for the development of novel cellular therapeutics. A number of sources of reprogramming potential have been identified, including oocytes, embryonic germ (EG) cells and embryonic stem (ES) cells. However, each of these sources of reprogramming factors is problematic, since they are either not freely available or have special growth requirements. Embryonal carcinoma (EC) cells are another source of pluripotent cells that, unlike ES and EG cells, do not usually require special growth conditions. Since they share many of the key characteristics of ES cells, such as pluripotency, EC cells may provide a readily amenable alternative source of reprogramming factors and could serve as a model for ES cells in this respect. Here we show that mouse EC cells can also function as donors of reprogramming factors. PEG-mediated fusion between murine EC cells (P19) and the cells of a human T-lymphoma cell line (CEM-GFP) resulted in inter-species hybrid colony formation. Colonies of hybrid cells displayed heterogeneity in cellular morphology as well as in their pattern of human gene expression. Expression of two human transcription factors characteristic of undifferentiated pluripotent stem cells, Oct-4 and Sox-2, was detected in the hybrid cells, demonstrating activation of endogenous human markers of pluripotency. Simultaneously, down-regulation of CD45, a marker present in lymphocytic cells, was observed in some hybrids. The detection of human specific markers of differentiation, such as nestin, lamininbeta1, and collagen IValpha1, indicates that fusion resulted in reprogramming of the human cells to reflect the differentiation potential of the murine EC partner.