Molecular mechanism of BMP signal control by Twisted gastrulation.

Twisted gastrulation (TWSG1) is an evolutionarily conserved secreted glycoprotein which controls signaling by Bone Morphogenetic Proteins (BMPs). TWSG1 binds BMPs and their antagonist Chordin to control BMP signaling during embryonic development, kidney regeneration and cancer. We report crystal structures of TWSG1 alone and in complex with a BMP ligand, Growth Differentiation Factor 5. TWSG1 is composed of two distinct, disulfide-rich domains. The TWSG1 N-terminal domain occupies the BMP type 1 receptor binding site on BMPs, whereas the C-terminal domain binds to a Chordin family member. We show that TWSG1 inhibits BMP function in cellular signaling assays and mouse colon organoids. This inhibitory function is abolished in a TWSG1 mutant that cannot bind BMPs. The same mutation in the Drosophila TWSG1 ortholog Tsg fails to mediate BMP gradient formation required for dorsal-ventral axis patterning of the early embryo. Our studies reveal the evolutionarily conserved mechanism of BMP signaling inhibition by TWSG1.

Dynamic and adaptive cancer stem cell population admixture in colorectal neoplasia.

Intestinal homeostasis is underpinned by LGR5+ve crypt-base columnar stem cells (CBCs), but following injury, dedifferentiation results in the emergence of LGR5-ve regenerative stem cell populations (RSCs), characterized by fetal transcriptional profiles. Neoplasia hijacks regenerative signaling, so we assessed the distribution of CBCs and RSCs in mouse and human intestinal tumors. Using combined molecular-morphological analysis, we demonstrate variable expression of stem cell markers across a range of lesions. The degree of CBC-RSC admixture was associated with both epithelial mutation and microenvironmental signaling disruption and could be mapped across disease molecular subtypes. The CBC-RSC equilibrium was adaptive, with a dynamic response to acute selective pressure, and adaptability was associated with chemoresistance. We propose a fitness landscape model where individual tumors have equilibrated stem cell population distributions along a CBC-RSC phenotypic axis. Cellular plasticity is represented by position shift along this axis and is influenced by cell-intrinsic, extrinsic, and therapeutic selective pressures.

Morphogen regulation of stem cell plasticity in intestinal regeneration and carcinogenesis.

The intestinal epithelium is a tissue with high cell turnover, supported by adult intestinal stem cells. Intestinal homeostasis is underpinned by crypt basal columnar stem cells, marked by expression of the LGR5 gene. However, recent research has demonstrated considerable stem cell plasticity following injury, with dedifferentiation of a range of other intestinal cell populations, induced by a permissive microenvironment in the regenerating mucosa. The regulation of this profound adaptive cell reprogramming response is the subject of current research. There is a demonstrable contribution from disruption of key homeostatic signaling pathways such as wingless-related integration site and bone morphogenetic protein, and an emerging signaling hub role for the mechanoreceptor transducers Yes-associated protein 1/transcriptional coactivator with PDZ-binding motif, negatively regulated by the Hippo pathway. However, a number of outstanding questions remain, including a need to understand how tissues sense damage, and how pathways intersect to mediate dynamic changes in the stem cell population. Better understanding of these pathways, associated functional redundancies, and how they may be both enhanced for recovery of inflammatory diseases, and co-opted in neoplasia development, may have significant clinical implications, and could lead to development of more targeted molecular therapies which target individual stem or stem-like cell populations.

Cross-sectional Survey of Medical student Attitudes to Research and Training pathways (SMART) in the UK: study protocol.

BACKGROUND: An understanding and appreciation of scientific research is a key quality of the modern clinician. Yet the Medical Schools Council has previously reported a reduction in the number of clinicians performing research. To explore the reasons for this difficulty, this multicentre, cross-sectional study aims to determine the medical student involvement and perceptions of research and research-orientated careers. It will additionally identify perceived barriers and incentives to participating in research as a student. METHODS AND ANALYSIS: This cross-sectional study of medical students at UK medical schools recognised by the General Medical Council will be administered using an online questionnaire. This will be disseminated nationally over a 2-month period through collaborative university medical school and student networks. The primary outcome is to determine the extent to which medical students are currently involved in research. Secondary outcomes include identifying the personal and demographic factors involved in incentivising and deterring medical students from becoming involved in research during medical school. This will be achieved using a selection of Likert scale, multiple-choice and free text questions. Ordinal logistic regression analysis will be performed to understand the association between specific factors and student involvement in research. This study will also characterise the proportion of medical students who are currently interested in conducting research in the future. ETHICS AND DISSEMINATION: Ethics approval has been obtained from the Medical Sciences Interdivisional Research Ethics Committee, Oxford, England. The results will be disseminated via publication in a peer-reviewed medical journal and may be presented at local, regional, national and international conferences by medical student collaborators.