Brief inactivation of c-Myc is not sufficient for sustained regression of c-Myc-induced tumours of pancreatic islets and skin epidermis

Background Tumour regression observed in many conditional mouse models following oncogene inactivation provides the impetus to develop, and a platform to preclinically evaluate, novel therapeutics to inactivate specific oncogenes. Inactivating single oncogenes, such as c-Myc, can reverse even advanced tumours. Intriguingly, transient c-Myc inactivation proved sufficient for sustained osteosarcoma regression; the resulting osteocyte differentiation potentially explaining loss of c-Myc's oncogenic properties. But would this apply to other tumours? Results We show that brief inactivation of c-Myc does not sustain tumour regression in two distinct tissue types; tumour cells in pancreatic islets and skin epidermis continue to avoid apoptosis after c-Myc reactivation, by virtue of Bcl-xL over-expression or a favourable microenvironment, respectively. Moreover, tumours progress despite reacquiring a differentiated phenotype and partial loss of vasculature during c-Myc inactivation. Interestingly, reactivating c-Myc in β-cell tumours appears to result not only in further growth of the tumour, but also re-expansion of the accompanying angiogenesis and more pronounced β-cell invasion (adenocarcinoma). Conclusions Given that transient c-Myc inactivation could under some circumstances produce sustained tumour regression, the possible application of this potentially less toxic strategy in treating other tumours has been suggested. We show that brief inactivation of c-Myc fails to sustain tumour regression in two distinct models of tumourigenesis: pancreatic islets and skin epidermis. These findings challenge the potential for cancer therapies aimed at transient oncogene inactivation, at least under those circumstances where tumour cell differentiation and alteration of epigenetic context fail to reinstate apoptosis. Together, these results suggest that treatment schedules will need to be informed by knowledge of the molecular basis and environmental context of any given cancer

Re-expression of IGF-II is important for beta cell regeneration in adult mice

Background The key factors which support re-expansion of beta cell numbers after injury are largely unknown. Insulin-like growth factor II (IGF-II) plays a critical role in supporting cell division and differentiation during ontogeny but its role in the adult is not known. In this study we investigated the effect of IGF-II on beta cell regeneration. Methodology/Principal Findings We employed an in vivo model of ‘switchable’ c-Myc-induced beta cell ablation, pIns-c-MycERTAM, in which 90% of beta cells are lost following 11 days of c-Myc (Myc) activation in vivo. Importantly, such ablation is normally followed by beta cell regeneration once Myc is deactivated, enabling functional studies of beta cell regeneration in vivo. IGF-II was shown to be re-expressed in the adult pancreas of pIns-c-MycERTAM/IGF-II+/+ (MIG) mice, following beta cell injury. As expected in the presence of IGF-II beta cell mass and numbers recover rapidly after ablation. In contrast, in pIns-c-MycERTAM/IGF-II+/− (MIGKO) mice, which express no IGF-II, recovery of beta cell mass and numbers were delayed and impaired. Despite failure of beta cell number increase, MIGKO mice recovered from hyperglycaemia, although this was delayed. Conclusions/Significance Our results demonstrate that beta cell regeneration in adult mice depends on re-expression of IGF-II, and supports the utility of using such ablation-recovery models for identifying other potential factors critical for underpinning successful beta cell regeneration in vivo. The potential therapeutic benefits of manipulating the IGF-II signaling systems merit further exploration

Deciphering c-MYC-regulated genes in two distinct tissues.

BACKGROUND: The transcription factor MYC is a critical regulator of diverse cellular processes, including both replication and apoptosis. Differences in MYC-regulated gene expression responsible for such opposing outcomes in vivo remain obscure. To address this we have examined time-dependent changes in global gene expression in two transgenic mouse models in which MYC activation, in either skin suprabasal keratinocytes or pancreatic islet β-cells, promotes tissue expansion or involution, respectively. RESULTS: Consistent with observed phenotypes, expression of cell cycle genes is increased in both models (albeit enriched in β-cells), as are those involved in cell growth and metabolism, while expression of genes involved in cell differentiation is down-regulated. However, in β-cells, which unlike suprabasal keratinocytes undergo prominent apoptosis from 24 hours, there is up-regulation of genes associated with DNA-damage response and intrinsic apoptotic pathways, including Atr, Arf, Bax and Cycs. In striking contrast, this is not the case for suprabasal keratinocytes, where pro-apoptotic genes such as Noxa are down-regulated and key anti-apoptotic pathways (such as Igf1-Akt) and those promoting angiogenesis are up-regulated. Moreover, dramatic up-regulation of steroid hormone-regulated Kallikrein serine protease family members in suprabasal keratinocytes alone could further enhance local Igf1 actions, such as through proteolysis of Igf1 binding proteins. CONCLUSIONS: Activation of MYC causes cell growth, loss of differentiation and cell cycle entry in both β-cells and suprabasal keratinocytes in vivo. Apoptosis, which is confined to β-cells, may involve a combination of a DNA-damage response and downstream activation of pro-apoptotic signalling pathways, including Cdc2a and p19(Arf)/p53, and downstream targets. Conversely, avoidance of apoptosis in suprabasal keratinocytes may result primarily from the activation of key anti-apoptotic signalling pathways, particularly Igf1-Akt, and induction of an angiogenic response, though intrinsic resistance to induction of p19(Arf) by MYC in suprabasal keratinocytes may contribute.RIGHTS : This article is licensed under the BioMed Central licence at http://www.biomedcentral.com/about/license which is similar to the 'Creative Commons Attribution Licence'. In brief you may : copy, distribute, and display the work; make derivative works; or make commercial use of the work - under the following conditions: the original author must be given credit; for any reuse or distribution, it must be made clear to others what the license terms of this work are

Micro-Net: A unified model for segmentation of various objects in microscopy images

Object segmentation and structure localization are important steps in automated image analysis pipelines for microscopy images. We present a convolution neural network (CNN) based deep learning architecture for segmentation of objects in microscopy images. The proposed network can be used to segment cells, nuclei and glands in fluorescence microscopy and histology images after slight tuning of input parameters. The network trains at multiple resolutions of the input image, connects the intermediate layers for better localization and context and generates the output using multi-resolution deconvolution filters. The extra convolutional layers which bypass the max-pooling operation allow the network to train for variable input intensities and object size and make it robust to noisy data. We compare our results on publicly available data sets and show that the proposed network outperforms recent deep learning algorithms

A simple matter of life and death : the trials of postnatal beta-cell mass regulation

Pancreatic beta-cells, which secrete the hormone insulin, are the key arbiters of glucose homeostasis. Defective beta-cell numbers and/or function underlie essentially all major forms of diabetes and must be restored if diabetes is to be cured. Thus, the identification of the molecular regulators of beta-cell mass and a better understanding of the processes of beta-cell differentiation and proliferation may provide further insight for the development of new therapeutic targets for diabetes. This review will focus on the principal hormones and nutrients, as well as downstream signalling pathways regulating beta-cell mass in the adult. Furthermore, we will also address more recently appreciated regulators of beta-cell mass, such as microRNAs

Spermatogenesis in the rat: Isolation of post-meiotic germ cells and characterisation of stage-specific gene expression

Spermatogenesis is largely dependent on stage-specific gene expression that takes place within the developing germ cell, and requires the close association between each spermatogenic cell stage and the supporting Sertoli cell. The aim of my thesis was to isolate purified populations of the post-meiotic germ cell (round spermatids) from the rat, and to characterise genes expressed at this cell stage which might encode proteins targeted to the acrosome A novel panning technique was devised which allowed the isolation of 95% pure round spermatids from adult rat testis, exceeding purities obtained by sedimentation through a BSA gradient. Subsequently, two experimental strategies were devised which included the use of antiserum raised against mammalian acrosomal membranes to 1) immunologically isolate specific polysomal mRNA or 2) to screen a human testis cDNA expression library. Although limitations were encountered using the polysome approach, a 2 kb cDNA clone (352) was isolated following library screening, which appeared to derive from a highly conserved, novel gene Low levels of 352 mRNA expression were evident in a range of human tissues, but were clearly up-regulated in the testis Before 15 days of age, 352 mRNA was not apparently expressed in the rat testis. Between 15 and 22 days of age, expression was at a very low level, coinciding with the initial accumulation of pachytene spermatocytes within the seminiferous epithelium. However, in males of 27 days or older, 352 mRNA was significantly elevated. This expression was concomitant with the appearance and subsequent differentiation of stage 1-5 spermatids. Surprisingly, Northern blot analysis indicated that round spermatids were not the cell type responsible for the elevated levels of expression of 352 mRNA in 27 day old rats. It was hypothesized that this up-regulation might be the result of predominant expression in Sertoli cells, such that, the appearance of round spermatids could induce Sertoli cells to synthesize 352 mRNA, and subsequently transfer the protein product to round spermatids where it may be targeted to the acrosome

Engineering beta cell mass regulation in diabetes

?-cell failure, encompassing a range of aberrant cellular processes from dysfunction to death, has long been recognised as the central defect in Type 1 Diabetes Mellitus (T1DM), but is now also accepted as a major factor in essentially all other types of diabetes, notably the “epidemic” variant, Type 2 Diabetes (T2DM). However, the mechanisms involved differ as exemplified by prominent role ascribed to the immune system and extrinsic pathway of apoptosis in T1DM and to metabolic insults (gluco- and lipo- toxicity) in T2DM. Intriguingly, common ground is emerging, whereby ?-cell renewal, death and plasticity are influenced by combinations of environmental factors, including metabolic changes, immune processes, cell-cell contacts and growth factors acting on ?-cells rendered either resistant or prone to cell death by intracellular signaling pathways, such as the IRS2/PI3K/AKT/mTOR pathway and master regulatory proteins such as c-Myc. Moreover, maintaining a functional ?-cell mass does not merely require avoiding destruction and dysfunction, but also renewal by self-replication and/or differentiation from precursors. Finally, the fact that processes regulating growth and death are intimately linked and also impact on function creates intriguing conundrums- for instance is there a maximum number/proportion of ?-cells that can be replicating at any one time without compromising ability to control blood glucose. This is very pertinent as rising glucose could accelerate ?-cell losses and or further compromise renewal thus constituting a spiral to catastrophe and transition from compensated insulin resistance to overt diabetes. Important new therapies are exploiting knowledge of beta cell mass regulation and function and further advances may finally unleash the potential of ?-cell targeted treatments and even cell-based therapies for diabetes. This exciting area will be the focus of this review

c-Myc and downstream targets in the pathogenesis and treatment of cancer

The c-Myc oncoprotein is a master regulator of genes involved in diverse cellular processes. Situated upstream of signalling pathways regulating cellular replication/growth as well as apoptosis/growth arrest, c-Myc may help integrate processes determining cell numbers and tissue size in physiology and disease. In cancer, this 'dual potential' allows cMyc to act as its own tumour suppressor. Evidently, given that deregulated expression of c-Myc is present in most, if not all, human cancers (Table 1) and is associated with a poor prognosis, by implication these in-built 'failsafe' mechanisms have been overcome. To explore the complex activity of c-Myc and its potential as a therapeutic target 'post-genome era' technologies for determining global gene expression alongside advanced new models for the study of tumourigenesis in vivo have proved invaluable. Thus, many recent studies have provided encouragement for the therapeutic targeting of c-Myc in cancer and have revealed new protein targets for manipulating aspects of c-Myc activity. The remarkable regression of even advanced and genetically unstable tumours, seen following deactivation of c-Myc in various models is particularly exciting. This review will discuss what is known about the role of c-Myc in growth deregulation and cancer and will conclude with a discussion of the most promising recent developments in Myc-targeted therapeutics