First person – Daniel Williams

Daniel Williams

How would you explain the main findings of your paper in lay terms?

All organs in the human body originate from the same single cell following fertilisation of an egg. To become a fully formed organ distinct from other tissues, cells in a developing embryo need to follow a set of instructions that specify that different cell types are produced at the right place, at the right time and in the correct number. These instructions partly come in the form of messengers released from other nearby cells that guide their neighbours towards the correct fate. In the brain, receptors at the surface of developing brain cells can recognise the presence of messengers in their nearby environment, which tell the cell to become a specific type of brain cell, such as a neuron. The amount of receptor at the cell surface needs to be maintained through continued delivery from intracellular compartments; when the delivery process goes wrong, the receptor is no longer available to sense the external messengers that help to determine the fate of progenitor brain cells. As a result, the brain may then fail to develop normally, leading to problems with brain function later in life. In our work published in JCS, we established a method to visualise whether cells in the developing zebrafish brain can recognise the presence of a specific model messenger and found that the absence of a protein that co-ordinates the delivery of receptors to the cell surface impairs the ability of developing brain cells to recognise this messenger. We believe this defect in receptor delivery and messenger recognition may underlie neurodevelopmental impairments associated with an inherited human genetic disorder, Lowe syndrome.

Were there any specific challenges associated with this project? If so, how did you overcome them?

Performing microinjections of one nanolitre of an endocytic tracer into the brain ventricle at a very early stage of zebrafish development (24 h post fertilization, when whole embryos are less than 3 mm in length) and imaging soon after injection on a microscope with enough resolution to make out the endocytic compartments we were interested in was tricky to begin with! On top of that, getting through enough injections in the day to give a big enough dataset to analyse was also difficult. It helped that other labs had published methods for mounting the embryos in a way that allows imaging of the ventricle (Graeden and Sive, 2009; doi: 10.3791/1217). Otherwise, lots of trial and error, a high-quality lab timer and a good lunch (thanks to Greggs and the Michael Smith café) were all essential to coming up with and sticking to a workable protocol.

When doing the research, did you have a particular result or ‘eureka’ moment that has stuck with you?

We had thought that endocytosis of RAP, an LRP receptor-binding protein that we used to study neuroepithelial endocytosis, would mostly be dependent on Lrp2 in neuroepithelial cells (as Lrp2 is relatively well expressed in the neuroepithelium) and we would see a significant reduction in endocytosis of RAP in Lrp2 knockout embryos. It was surprising to us then that RAP uptake in embryos without Lrp2 was almost as efficient as wild-type fish. This is a nice demonstration of cell type-specific differences in vivo as Martin [Lowe] and others have shown previously that RAP endocytosis in the zebrafish pronephros is entirely dependent on Lrp2 (Oltrabella et al., 2015; doi: 10.1371/journal.pgen.1005058; Anzenburger et al., 2006; doi: 10.1242/jcs.02954). Quite excitingly, this result hints at the presence of additional LRP receptors at the apical surface of neuroepithelial cells, and it might make important contributions to understanding endocytosis of LRP receptor ligands required for brain development in zebrafish and potentially in mammals too.

Why did you choose Journal of Cell Science for your paper?

I have read many good papers in JCS over the years [including one from my current boss, Andrew Peden (Ampah et al., 2018; doi: 10.1242/jcs.212498)], and Martin, my PhD supervisor, has also published many nice papers in this journal (Williams et al., 2007; doi: 10.1242/jcs.012112; Roboti et al., 2015; doi: 10.1242/jcs.166710; Hellicar et al., 2022; doi 10.1242/jcs.258879). There is lots of high-quality research being published in JCS and it’s one of a clutch of journals I regularly check with interest for any exciting new papers, so I was very happy that we were able to publish this work here.

What motivated you to pursue a career in science, and what have been the most interesting moments on the path that led you to where you are now?

For some reason, I was fascinated by the idea of things being moved around in cells by the process of vesicular transport, and that was all I needed to start doing a PhD without fully knowing what I was getting myself into. I've drifted away from what I was initially interested in and ended up working on things I never thought I would, but it's great to be able to combine my prior experience and interests and potentially come up with something unique. I'm sure that, as is true for most people working in a lab, the excitement of new results and discoveries and being able to test new ideas is what keeps me going day to day – hopefully I can make a worthwhile contribution to science and biomedical research in the long run.

What's next for you?

I still study aspects of endocytic trafficking in my current lab, but no longer work with zebrafish. I would at some point like to work with fish again and apply all the methods I have learned working with cell culture models to zebrafish, as I think they are a fantastic model organism to work with, particularly when it comes to imaging processes at the tissue level and, as shown in our paper, at the sub-cellular level. There is a lot of unique cell biology in the developing brain in particular just waiting to be explored further.