Maria P. De Miguel

Cdc25b phosphatase is required for resumption of meiosis during oocyte maturation

In a wide variety of animal species, oocyte maturation is arrested temporarily at prophase of meiosis I (ref. 1). Resumption of meiosis requires activation of cyclin-dependent kinase-1 (CDK1, p34cdc2), one component of maturation-promoting factor (MPF). The dual specificity phosphatases Cdc25a, Cdc25b and Cdc25c are activators of cyclin-dependent kinases; consequently, they are postulated to regulate cell-cycle progression in meiosis and mitosis as well as the DNA-damage response. We generated Cdc25b-deficient (Cdc25b−/−) mice and found that they are viable. As compared with wildtype cells, fibroblasts from Cdc25b−/− mice grew vigorously in culture and arrested normally in response to DNA damage. Female Cdc25b−/− mice were sterile, and Cdc25b−/− oocytes remained arrested at prophase with low MPF activity. Microinjection of wildtype Cdc25b mRNA into Cdc25b−/− oocytes caused activation of MPF and resumption of meiosis. Thus, Cdc25b−/− female mice are sterile because of permanent meiotic arrest resulting from the inability to activate MPF. Cdc25b is therefore essential for meiotic resumption in female mice. Mice lacking Cdc25b provide the first genetic model for studying the mechanisms regulating prophase arrest in vertebrates.

Dissection of the c-Kit signaling pathway in mouse primordial germ cells by retroviral-mediated gene transfer

Establishment of the mammalian germ line is a prerequisite for fertility of the adult animal but we know surprisingly little about the molecular mechanisms regulating germ-line development in mammals. Signaling from the c-Kit receptor tyrosine kinase is essential for primordial germ cell (PGC) growth both in vivo and in vitro. Many downstream effectors of the c-Kit signaling pathway have been identified in other cell types but how these molecules control PGC survival and proliferation are unknown. Determination of the c-Kit effectors acting in PGCs has been hampered by the lack of effective methods to easily manipulate gene expression in these cells. We overcame this problem by testing the efficacy of retroviral-mediated gene transfer for manipulating gene expression in mammalian germ cells. We found that PGCs can be successfully infected with a variety of types of retroviruses. We used this method to demonstrate an important role for the AKT kinase in regulating PGC growth. Such technology for manipulating gene expression in PGCs will allow many of the molecular mechanisms regulating germ cell growth, behavior, and differentiation to be comprehensively analyzed.

Immunohistochemical analysis of the IL-6 family of cytokines and their receptors in benign, hyperplasic, and malignant human prostate

Interleukin‐6 (IL‐6) and its receptor have been implicated in prostate cancer progression. Because other members of the IL‐6 family such as leukaemia inhibitory factor (LIF) and oncostatin M (OSM) share gp130, the signal transduction subunit of their receptors, interpretation of the data without considering the expression of these cytokines and their specific receptor subunits could be misleading. The immunohistochemical pattern of the IL‐6 family and their receptor subunits in normal prostate, benign prostatic hyperplasia (BPH), and prostatic carcinoma (PC) was investigated. In normal prostates, gp130 and OSMRα were detected exclusively in the stroma and LIFRβ was very scarce. While IL‐6 was scarcely immunolocalized to the basal cells of the epithelium, OSM was detected in the stroma and LIF in both the epithelium and the stroma. This suggests an autocrine role for this family of cytokines in the stroma of normal prostates. In BPH, gp130 and OSMRα were detected both in the epithelium and in the stroma, whereas LIFRβ was localized only to the epithelium. IL‐6 localized preferentially to the epithelium, OSM to the stroma, and LIF to both compartments. Therefore, in addition to the autocrine role in the stroma, IL‐6 and OSM may play a paracrine role from the stroma to the epithelium in BPH. In PC, gp130 and OSMRα were detected both in the epithelium and in the stroma, increasing with rising Gleason grade, whereas LIFRβ was localized exclusively to the epithelium of low Gleason grade carcinomas. IL‐6, LIF, and OSM localized in all cell types, with immunostaining increasing with Gleason grade. These data suggest an autocrine role for these cytokines in the epithelial cells of PC. The distinct pattern of expression of LIFRβ exclusively in low Gleason grade carcinomas makes LIFRβ a candidate for malignancy diagnosis. The role of OSM mainly in high Gleason grade carcinomas makes OSM a putative target for prostate cancer therapy. Copyright

Determinants of Retroviral-Mediated Gene Delivery to Mouse Spermatogonia

Abstract Spermatogonia represent a new route to transgenesis in mice and potentially in some commercially important domesticated animals. In addition, these cells are also a potential target for viral integration in patients receiving somatic cell gene therapy. But the factors influencing retroviral transduction into spermatogonia are not well understood. Because retroviral transduction is affected in part by the proliferative status of the host cell, we developed an improved cell culture system in which spermatogonia survive and proliferate for several days. We used this system to test the ability of a variety of murine and avian retroviruses to infect spermatogonia. We investigated the factors influencing retroviral transduction of spermatogonia, including the proliferative status of the infected cell, the type of viral envelope, the type of retroviral long terminal repeat, and the method of viral delivery. Here we show that many of the widely used retroviral vector systems can be used to successfully transduce spermatogonia at high efficiency. Moreover, we show that retroviral delivery of MDM2, the major downregulator of p53, promotes spermatogonial survival in culture, suggesting that p53 plays a role in regulating spermatogonial apoptosis induced by growth factor deprivation. These results further demonstrate the usefulness of this novel system of targeting substances of interest to the testis. These data have important implications for improving animal transgenesis and for understanding the risks associated with somatic cell gene therapy.

Biointegration of corneal macroporous membranes based on poly(ethyl acrylate) copolymers in an experimental animal model.

Currently available keratoprosthesis models (nonbiological corneal substitutes) have a less than 75% graft survival rate at 2 years. We aimed at developing a model for keratoprosthesis based on the use of poly(ethyl acrylate) (PEA)-based copolymers, extracellular matrix-protein coating and colonization with adipose-derived mesenchymal stem cells. Human adipose tissue derived mesenchymal stem cells (h-ADASC) colonization efficiency of seven PEA-based copolymers in combination with four extracellular matrix coatings were evaluated in vitro. Then, macroporous membranes composed of the optimal PEA subtypes and coating proteins were implanted inside rabbit cornea. After a 3-month follow-up, the animals were euthanized, and the clinical and histological biointegration of the implanted material were assessed. h-ADASC adhered and survived when cultured in all PEA-based macroporous membranes. The addition of high hydrophilicity to PEA membranes decreased h-ADASC colonization in vitro. PEA-based copolymer containing 10% hydroxyethyl acrylate (PEA-HEA10) or 10% acrylic acid (PEA-AAc10) monomeric units showed the best cellular colonization rates. Collagen plus keratan sulfate-coated polymers demonstrated enhanced cellular colonization respect to fibronectin, collagen, or uncoated PEAs. In vivo implantation of membranes resulted in an extrusion rate of 72% for PEA, 50% for PEA-AAc10, but remarkably of 0% for PEA-HEA10. h-ADASC survival was demonstrated in all the membranes after 3 months follow-up. A slight reduction in the extrusion rate of h-ADASC colonized materials was observed. No significant differences between the groups with and without h-ADASC were detected respect to transparency or neovascularization. We propose PEA with low hydroxylation as a scaffold for the anchoring ring of future keratoprosthesis.

Adipose-derived mesenchymal stem cell administration does not improve corneal graft survival outcome.

The effect of local and systemic injections of mesenchymal stem cells derived from adipose tissue (AD-MSC) into rabbit models of corneal allograft rejection with either normal-risk or high-risk vascularized corneal beds was investigated. The models we present in this study are more similar to human corneal transplants than previously reported murine models. Our aim was to prevent transplant rejection and increase the length of graft survival. In the normal-risk transplant model, in contrast to our expectations, the injection of AD-MSC into the graft junction during surgery resulted in the induction of increased signs of inflammation such as corneal edema with increased thickness, and a higher level of infiltration of leukocytes. This process led to a lower survival of the graft compared with the sham-treated corneal transplants. In the high-risk transplant model, in which immune ocular privilege was undermined by the induction of neovascularization prior to graft surgery, we found the use of systemic rabbit AD-MSCs prior to surgery, during surgery, and at various time points after surgery resulted in a shorter survival of the graft compared with the non-treated corneal grafts. Based on our results, local or systemic treatment with AD-MSCs to prevent corneal rejection in rabbit corneal models at normal or high risk of rejection does not increase survival but rather can increase inflammation and neovascularization and break the innate ocular immune privilege. This result can be partially explained by the immunomarkers, lack of immunosuppressive ability and immunophenotypical secretion molecules characterization of AD-MSC used in this study. Parameters including the risk of rejection, the inflammatory/vascularization environment, the cell source, the time of injection, the immunosuppression, the number of cells, and the mode of delivery must be established before translating the possible benefits of the use of MSCs in corneal transplants to clinical practice.

The Role of the C-Kit/Kit Ligand Axis in Mammalian Gametogenesis

The survival of the germline is vital to the survival of all animal species. Failure of germ cells to survive or to differentiate properly in the animal can result in reduced fertility, or in some cases, complete sterility (1). In addition, defects in germline development can predispose individuals to development of cancer. For example, loss of germ cells from the ovary can be associated with premature ovarian failure, but can also dispose affected individuals to the development of ovarian cancer (2). Similarly in the male, loss of germ cells from the developing testis can be associated with the development of testicular teratocarcinoma (3). Testicular cancer is the most common malignancy in young men with a peak incidence from 18–35 yr of age (4, 5). This contrasts with the incidence of ovarian tumors, which show a higher incidence after 50 yr of age, as is the case with most other solid tumors (6). Thus, even in otherwise healthy individuals, survival of the germline is an important feature of adult homeostasis.

Regulation of Growth and Survival in the Mammalian Germline

Correct testicular function requires that a full complement of testicular germ cells be present in the adult testis. The germ-cell compartment of the testis is established early in embryonic development from the germline progenitor cells, termed primordial germ cells (PGCs). In mammals, the embryonic history of the germline has been well established. PGCs can be traced in the embryo by staining embryo sections for tissue nonspecific alkaline phosphatase (TNAP) and by antigenic markers recognized by rabbit polyclonal and mouse monoclonal antibodies (1–5). That these TNAP+ cells are indeed PGCs is confirmed by the fact that these cells are deficient or absent in mouse mutants that are sterile (6–9). PGCs arise outside of the gonad anlagen, and colonization of the gonad is brought about partly through the morphogenetic movements of the embryo and partly through active directed migration (2). During this period of gonad colonization the numbers of germ cells increases.

3’UTR Polymorphism in ACSL1 Gene Correlates with Expression Levels and Poor Clinical Outcome in Colon Cancer Patients

Strong evidence suggests that lipid metabolism (LM) has an essential role in tumor growth to support special energetic and structural requirements of tumor cells. Recently, overexpression of LM-related genes, apolipoproteins related to metabolic syndrome, and ACSL/SCD network involved in fatty acid activation have been proposed as prognostic markers of colon cancer (CC). Furthermore, activation of this latter lipid network has been recently demonstrated to confer invasive and stem cell properties to tumor cells promoting tumor aggressiveness and patient relapse. With the aim of elucidating whether any genetic variation within these genes could influence basal expression levels and consequent susceptibility to relapse, we genotype, in 284 CC patients, 57 polymorphisms located in the 7 genes of these lipid networks previously associated with worse clinical outcome of CC patients (ABCA1, ACSL1, AGPAT1, APOA2, APOC1, APOC2 and SCD), some of them related to CC aggressiveness. After adjusting with clinical confounding factors and multiple comparisons, an association between genotype and disease-free survival (DFS) was shown for rs8086 in 3’-UTR of ACSL1 gene (HR 3.08; 95% CI 1.69–5.63; adjusted p = 0.046). Furthermore, the risk T/T genotype had significantly higher ACSL1 gene expression levels than patients carrying C/T or C/C genotype (means = 5.34; 3.73; 2.37 respectively; p-value (ANOVA) = 0.019), suggesting a functional role of this variant. Thus, we have identified a “risk genotype” of ACSL1 gene that confers constitutive high levels of the enzyme, which is involved in the activation of fatty acids through conversion to acyl-CoA and has been recently related to increased invasiveness of tumor cells. These results suggest that rs8086 of ACSL1 could be a promising prognostic marker in CC patients, reinforcing the relevance of LM in the progression of CC.

Pluripotent Stem Cells of the Mammalian Early Embryo

The early embryo harbors the most amazing cells, the embryonic stem (ES) cells, pluripotent cells capable of generating all the tissues and cell types of a mature animal. Discovery and establishment of culture techniques able to maintain in culture human embryonic stem cells revolutionized the scientific community about a decade ago. In addition to ES cells, other lesser-known stem cells have their niche in the early embryo, such as trophoblast stem cells, and at later stages, epiblast stem cells and embryonic germ cells. This chapter will discuss current knowledge of these cell types, the results of their use in preclinical studies using animal models, and current cell therapies for human disease treatment.