Developmental Tuning of Turing Patterning

Lead Research Organisation: University of Edinburgh
Department Name: The Roslin Institute

Abstract

Our bodies arrange their own parts appropriately before we are born. We have only one of certain body parts (e.g. head, nose, spleen) and two of others (e.g. arm, eye, big toe) of, and these achieve their position through an equivalent of an embryo's Global Positioning System. However, still other structures, like hairs or nephrons of the kidney, are very numerous - too numerous to have a dedicated placing of each and every one of them. Instead, the body seems to use a simple "rule" to lay out these structures. This "rule" involves local interactions between cells which make sure that each follicle, nephron, or other structure, forms at a set distance from others of the same kind. Theoretical biologists have provided and proven general concepts that could underlie the operation of these "rules" and recent work by molecular biologists has substantiated and extended these theoretical ideas, identifying the specific genes and proteins that act as to set the "rule".

However, structures like hair follicles are not homogeneous across the body. For example, the eyebrows and scalp produce thicker hair types that mark these parts of the skin as being different from, for example, the forehead, which has very small, fine hairs. In this proposal we aim to understand how such distinctions in pattern, in this case of hair follicles serving as an example of other repeated structures, can be achieved. In essence, we will go up one level in organisation to understand how the size and spacing "rule" can be varied in different locations. This we will do by studying hair follicle formation on different parts of the mouse skin, with a focus on the various whiskers because of their distinctive pattern. Our project will be a combination of molecular and cell biology in analysing and manipulating the signals that pass between cells and mathematical simulations to interpret and guide the experimentation. Experiments will be done primarily on cultured skin samples, sparing use of intact animals. The intended outcome is to understand at both molecular and conceptual levels how the body can utilise a single pattern forming system by tuning in different regions to achieve a complex anatomy.

Technical Summary

The overall objective of this programme of work is to understand how a pattern forming system can be modulated to yield different outputs in different body regions. We will map signalling pathway activities by assessing pathway targets in different regions of the skin and determine growth parameters across the crucial stages of embryonic mouse hair follicle patterning. We will go on to modulate BMP, WNT and retinoic acid signalling on different parts of the body and assess pattern output, then determine the interactions between these pathways at the molecular level.

We will extract spatial placode distributions from experimental data, together with summary measures and statistics, such as the mean and variance of the inter-placode distance, i.e. the effective pattern wavelength. In turn this will allow comparison with detailed simulation and the estimation of the parameters required to match observation and theory, together with systematically classifying how close theory and experiment actually are, for hypothesis testing and also hypothesis generation and modelling development, for instance with regard to the understanding and modelling representation of the impact of retinoic acid. This can also be pursued on a regional basis to assess whether simple modulation can explain the spatial variation in different regions of the skin. Such comparisons will require systematic tools for data capture, which extract the evolution of the growing skin surface and capture the spatial distribution of placodes on this skin. Similarly, the systematic comparison of theory and observation will require the use of tools such as random forests and approximate Bayesian computation whilst the simulations will entail the solution of systems of reaction diffusion equations on evolving curved surfaces.

Planned Impact

This project will illuminate mechanisms of embryonic development and pattern formation, achieved by integrating tissue growth and intercellular signalling mechanisms within a rigorous mathematical framework.

Future practical implications arising from this work lie in understanding how specific signalling pathways are integrated to control appropriate organ development. Retinoic acid is already used as a dermatological treatment, for example in treatment of acne, and the EDA protein is in phase 2 clinical trial for treatment of the congenital condition hypohidrotic ectodermal dysplasia, caused by mutation of the gene encoding this protein (Edimer Pharmaceuticals). The interactions between these pathways and the others studied will help guide the practical use of these agents in therapies. The recent ability to target the EDA signalling pathway using newly developed reagents enables this pathway to be modulated, potentially including the emerging ability to use stimulators of this pathway in adult tissue regeneration of degenerated glandular structures, based on recent findings (e.g. Pharmacological activation of the EDA/EDAR signaling pathway restores salivary gland function following radiation-induced damage. Hill G, Headon D, Harris ZI, Huttner K, Limesand KH. PLoS One. 2014 9:e112840.). DH has funding from Edimer Pharmaceuticals to examine the potential of this pathway for therapeutic use in pre-clinical models. Growth of hair in adult skin is based on the action of the same signals as those operating in embryonic development to order the locations of hair primordia, thus industry impact in the area of identifying means to modulate hair growth through targetable molecular pathways is a later outcome from these studies. Such developments also have prospective impact in animal husbandry for agriculture, for instance enhancing sheep wool density to improve yield or reducing feather density to facilitate heat stress resistance in hotter climates.

In addition, the specific signalling interactions under study - those of the EDA, WNT, BMP and retinoic acid pathways - are relevant to the development of many vertebrate organs and will stimulate studies regarding the integration of these signals in a range of tissues. For instance, WNT signalling is a prime target for numerous cancer interventions, and thus its signalling, and how this might be quantitatively modelled, is of interest outside academia in the oncology research supporting the drug discovery programmes of large Pharmaceutical companies. One of us (EAG) has found parameter estimation a major challenge in work recently initiated with F. Hoffman LaRoche Ltd [via an industrially sponsored student at the pre-publication phase of her DPhil] exploring the modelling of a signalling pathway. Hence developing tools, which will be made freely available, for exploiting spatial data in parameter estimation, hypothesis testing and generation also has the prospect of impact not only in developmental biology but also in industrially focussed research. Furthermore, this prospective impact is not just scientific but also ethical, as it develops our ability to maximise the use of spatial data from animal experiments, noting that advances in imaging entail that spatial data is often readily available.

Finally, the general public has an interest in the beautiful patterns seen in nature and in the origins of these patterns. The public impact of this project upon the public will be enhanced by the 'real-world' nature of the model system studied; the distribution of hair of different types across the body. This model is easily appreciated by a lay audience and, combined with the striking images produced in studies of spatial patterning, this area is ideal for public engagement activities. In this regard the use of cultured skin tissues and computer simulation where appropriate in the project, rather than experimentation on intact animals, will aid public engagement and acceptance.
 
Description We have uncovered a network of signals that acts to position the hair follicles on the body of mammals, and shown that this network can be circumvented to allow cells to generate hair follicles in the absence of some of the normal signals. We have also focussed on whisker hair formation and defined the process and key molecular signals acting in different regions of the face, building a picture of how this complex sensory system in generated. This system is much more complex than that which produces the hair follicles on most of the body as it reads out many different influences as the face is assembled. We have found that the major influence from the tip of the growing nose is BMP, and the major influence from the upper side of the snout (away from the mouth) is retinoic acid. For molecular analyses, we have identified a novel point of contact between the retinoic acid and BMP signalling pathways and are trying to identify exactly how this operates. We have derived a novel mathematical model, in partnership with collaborators, to describe the process of whisker patterning and to explain key experimental manipulations. We have also addressed how this system defined in mammals might be applied to understand feather formation in birds, finding molecular similarities but some stark differences regarding the importance of cell movement between these species.
Exploitation Route We have found that the effect of a molecule called BMP, which is widely used in the body to construct and maintain tissues, is enhanced by a second molecule called retinoic acid (RA). One line of work that we are focussing on is how many tissues or cells experience this effect, and to explain how it comes about. As RA is very important for skin function, and is already used as a treatment for several conditions, the information produced in the project could be used in dermatology and perhaps other areas to improve the use of RA as a medicine.
Sectors Pharmaceuticals and Medical Biotechnology

 
Description Marie Sklodowska Curie fellowship
Amount € 195,455 (EUR)
Organisation European Commission 
Sector Public
Country European Union (EU)
Start 09/2016 
End 09/2018
 
Description Crowd Science on BBC World Service 
Form Of Engagement Activity A broadcast e.g. TV/radio/film/podcast (other than news/press)
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact Interviewed on developmental biology related to this project for the BBC World Service programme Crowd Science - episode 'How does a single cell become me?' Broadcast international to listeners of the World Service.
Year(s) Of Engagement Activity 2019
URL https://www.bbc.co.uk/sounds/play/w3csz1sw
 
Description Press release pattern formation 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Media (as a channel to the public)
Results and Impact Press release and attributed quote on our work, published, on biological pattern formation February 2019
Year(s) Of Engagement Activity 2019
URL https://bbsrc.ukri.org/news/food-security/2019/190221-n-understanding-feather-formation-could-lead-t...