Young Lab ~ Available Projects

Project 1 - Factors influencing the migration of neural crest cells along the gut

During the development of the enteric nervous system (ENS), neural precursors must first migrate into and colonize the entire gastrointestinal tract (gut). Enteric neurons and glial cells arise from two different sources, vagal and sacral level neural crest cells. Vagal neural crest cells colonize the entire gut, whereas sacral cells colonise only the distal hindgut.

Cells derived from the vagal level neural crest first enter the foregut of embryonic mice around E9.5 and migrate caudally along the gut. Sacral level neural crest cells emigrate from the neural tube and coalesce into the ganglia of the pelvic plexus, adjacent to the distal hindgut.

After a delay of at least 4 days, sacral neural crest cells enter the distal hindgut. However, the time at which they enter the hindgut and their migratory route is still unknown. The delayed entry of sacral neural crest cells into the distal hindgut could be due to the transient expression of repulsive molecules in the distal hindgut, or to an early absence of attractive molecules (or their receptors on the sacral neural crest cells).

Our laboratory has devised in vitro methods for assaying the migration of neural crest cells along explants of embryonic mouse gut by using mice in which enteric neural crest cells express GFP or lacZ (Fig. 1).

We also have methods to examine whether particular molecules are inhibitory or repulsive by growing transverse slices of gut on collagen gels (Fig. 2).

Possible projects to be undertaken to investigate the molecular control of enteric neural crest cell migration include:

1. Determine the expression of known guidance molecules within the developing hindgut (including members of the semaphorin family and some cell adhesion molecules), and whether these molecules influence neural crest migration by using in vitro assays.
2. We have shown previously that neural crest cells migrate alongside growing axons as they migrate down the gut. Some molecules that influence neural activity have been shown to influence neural migration or axon extension in other parts of the nervous system. You could examine the effect of TTX (which blocks action potentials) nitric oxide synthase inhibitors and N-type calcium channel blockers on neural crest cell migration and differentiation through explants of gut.

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Project 2 - Role of gap junctions in enteric neuron development

Gap junctions are channels between cells formed by protein molecules that allow inorganic ions and other small water-soluble molecules (up to about 1 kDa in size) to pass directly from one cell to another. Cells joined by gap junctions are therefore coupled both electrically and metabolically. The channels connecting neighbouring cells are called connexons.

Cell coupling via gap junctions between some mature, electrically excitable cells plays an important functional role. However, many cell types that are not coupled when mature, are transiently coupled to other cells during development. In the central nervous system, gap junctions are present transiently between sub-types of developing neurons. Coupling appears to be an important form of cell-to-cell communication in early brain development, and plays a significant role in the differentiation of neurons.

The main aim of the experiments in this project is to use intracellular injection of different molecular weight molecules into neural crest-derived cells within the embryonic mouse gut to determine whether coupling exists between neural crest-derived cells. If coupling is observed, we will determine whether the coupling occurs between (a) undifferentiated neural crest-derived cells only, (b) undifferentiated neural crest-derived cells and cells that have started to differentiate into neurons (ie all neural crest-derived cells within the embryonic gut), or (c) developing enteric neurons only.

You could then go on to examine: (a) the role of coupling in the development of the enteric nervous system, by determining the effect of blocking coupling on the differentiation and maturation of enteric neurons (there are a number of drugs available that shut down gap junctions) (b) what factors regulating the extent of coupling (ie pH, neurotransmitters, calcium etc).

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Project 3 - Factors influencing the differentiation of different types of enteric neurons

Different types of enteric neurons develop at different times. In the developing retina it has been shown that differentiating neurons influence the development of other neural cells. In this project you will examine whether soluble factors produced by other enteric neurons or by non-neuronal elements in the gut influence the differentiation of enteric neurons. You could examine the types of neurons that differentiate in:

1. explants of E11.5 gut cultured alone
2. explants of E11.5 gut cultured with medium conditioned by P0 gut that contains enteric neurons
3. explants of E11.5 gut cultured with medium conditioned by mutant P0 gut that lacks enteric neurons
4. P0 gut cultured alone
5. P0 gut cultured with medium conditioned by E11.5 gut

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Project 4 - Development of gastrointestinal motility

Co-supervised by Assoc Prof Joel Bornstein , Department of Physiology.

Little is known about the patterns of motility displayed by the developing gut and the role of enteric neurons in their control. Recently, methods have been established for analyzing gut motility in which maps of gut diameter as functions of length along the intestine and time (spatio-temporal maps) are generated from video images (Fig. 3). This method is currently in use in Assoc Prof Bornstein's laboratory.

In this project you will examine how the adult forms of motility develop and the role of enteric neurons in their control by using mutant mice that lack enteric neurons in the in test ine.