Professor Kim Dale FRSB
Analysis of Primitive Streak stem cells and the role of Notch in regulating cell fate choice within these multipotent progenitor pools
The broad interest of the laboratory aims to further our understanding of how several genetic interactions come into play at the earliest stages of development to build the developing embryo. Primitive streak formation is reputed as being 'the most important time in ones life' since it generates the three germ layers of the embryo proper. The progenitor cells of these three germ layers ingress into the embryonic organiser and the primitive streak where they form resident populations of stem cells for multiple tissue types. One main focus of the laboratory will be to gain a deeper understanding of the mechanism of regulation of these stem cells both in the mouse and the chick system. We will initially try to identify the location of the stem cell pools. We will then investigate the function of potential candidate signalling pathways involved in i)maintaining this stem cell state and ii) biasing these progenitors to contribute daughter cells to specific tissues inthe developing embryonic axis.
We have shown that Notch signaling is key in regulating cell fate choice within these multipotent progenitor pools which holds a promise for developing cells of desired type in in vitro ES cell culture. Following the production of the neural tube (NT), elaboration of neuronal identity begins. The NT is exquisitely patterned to eventually form the complex neuronal domains in the adult spinal cord. The correct allocation of cells to particular neuronal fates in the correct spatial location is critical for the formation of the CNS. Patterning of the NT along the dorso ventral axis into specific regionalised neuronal subtypes is primarily achieved by the morphogen Sonic hedgehog (Shh). SHH is released from two ventrally located structures which derive from the embryonic organizer, namely notochord and floor plate which results in a concentration gradient of SHH being set up along the ventral to dorsal axis which then induces expression of specific transcription factors at distinct distances from the source of the signal. We are investigating the role that Notch plays in regulating the competence of cells to respond to the SHH morphogen during DV patterning and cell fate specification in the NT.
Investigation into the molecular regulation of the Segmentation clock.
Segmentation is a universal feature of the body plan of all vertebrate species. This is most clearly seen in the vertebrate axial skeleton which is comprised of a series of segments, namely the ribs and articulating vertebrae. In vertebrate species the process of segmentation begins with the sequential formation of structures called somites, which later develop into the ribs and vertebrae. Interference with this process of somitogenesis can lead to serious segmental defects and associated pathologies, such as Spondylocostal dysostosis (SCD). The aetiology of most Abnormal vertebral segmentation (AVS) Syndromes is unknown. However one signalling pathway that has been associated with several human disorders such as SCD is the Notch signalling pathway. Somitogenesis is regulated by a molecular oscillator which drives oscillating gene expression in the paraxial mesoderm from which somites arise. The key components of the segmentation clock are intracellular components of the Notch, Wnt and FGF pathways. We have shown in mouse and chick, Notch activity is essential for both dynamic expression of all clock genes and for somite formation. Outstanding questions in the field which we are addressing are as follows:
1) Oscillating genes are negative regulators of the pathways which activate them. It seems clear how these negative feedback loops regulate oscillatory gene expression intracellularly. We are investigating how patterns of gene expression are propagated across the PSM.
2) How is the pace of clock gene oscillations regulated?
3) What is the level of cross talk and hierarchy within and between the Notch, Wnt and FGF pathways within the molecular oscillator.
161091: MYC activity is required for maintenance of the Neuromesodermal Progenitor signalling network and for correct timing of segmentation clock gene oscillations; Dale and colleagues
Where and when: the central role of Myc in somite formation
*Figure 7B (y’)
Although Myc transcription factors are extensively studied in the context of cancer, the inclusion of cMyc as one of the Yamanaka factors has renewed research into their roles in stem cell maintenance and embryogenesis. Myc is expressed throughout embryogenesis, but its spatiotemporal distribution has been poorly characterised. In this study, Kim Dale and colleagues sought to clarify the expression and function of Myc during early embryogenesis in mice, focussing on its role in body axis elongation and somite formation. The authors combine pharmacological inhibition and conditional loss-of-function genetic approaches to interrogate the role of Myc genes in the differentiation of neuromesodermal progenitors (NMPs) – a progenitor population that gives rise to posterior neural and mesoderm lineages. Their results show that cMyc is indeed required for the proper timing of somite formation through the regulation of NOTCH signalling. Additionally, they demonstrate that Myc operates in a positive feedback loop with WNT and FGF signalling in NMPs to facilitate axial elongation and to maintain accurate timing of the segmentation clock. This work places Myc activity at the centre of a signalling circuit that coordinates body axis elongation during embryogenesis.