Nervous system in annelids: Pioneers join from both ends

The development of the nervous system is governed by patterning processes that define the number and position of neurons. While such studies in different animal groups have been important for developmental and evolutionary insights, the data on the first neurons or the pioneer neurons, particularly in the large invertebrate group of lophotrochozoans, is lacking. In their recent publication, the Hausen group set out to investigate the early stages of nervous system development in the annelid Malacoceros fuliginosus.

First, they identified the cells that are capable of initiating the formation of the entire neural scaffold. A single posterior neuron prefigures the main course of the ventral nerve cord (VNC), while in the anterior region, the brain is initiated by a single apical neuron and a pair of sensory cells link all the ciliated prototroch cells.

Next, they did a detailed neural gene expression analysis at short time intervals. This allowed them to capture the transient and dynamic nature of proneural gene expression, which revealed an anterior and posterior development of neural progenitors. They propose that an anterior and posterior origin of the nervous system is ancestral in annelids.

Due to its distinct morphology and location, the Hausen group could track the development of the VNC pioneer neuron. They found that it is specified at an early stage by the dynamic and transient expression of multiple proneural genes. By cell-lineage study, they also identified that the VNC pioneer neuron originates from the 2d (2d²²¹) blastomere. This not only provides a basis for further cell-lineage studies within annelids and lophotrochozoans but also provides insights into nervous system development and evolution.

With debates on nervous system evolution still ongoing, comparative studies at the level of pioneer neurons could be another aspect to help resolve this enigma.

We interviewed the first author of this paper, Suman Kumar:

- Can you say something about your educational and scientific background and what interested you about working in the Sars Centre?

I did my master’s studies in Genetics at the University of Helsinki. During that time, I became interested in neurogenetics and neural development. I did my thesis work on a similar topic where I studied the diversity of GABAergic neurons in the vertebrate brainstem. 

Then I started to look for PhD opportunities in nervous system development, during which I stumbled upon the Marie Curie PhD position at the Sars centre, which seemed very attractive. The project was also part of a lab network from all over Europe, so I felt it would also be a perfect opportunity to learn about animal diversity and evolution.

- In a short time, your group has published two papers, where you are first- and shared first author. Are these papers related to each other in some way?

The other paper is about a newly described opsin type called xenopsin, which, along with the well-known c-opsins and r-opsins, seems to have an important role in animal vision (particularly in protostomes). Although the two papers are not entirely related, it does provide insights on how flexible cell types can be, which is an important aspect to consider for comparative studies on cell type evolution.   

- What type of research would you like to do during your first postdoc and in the long term future if you decide to stay in science ?

I would like to work on neuronal regulation and function. I hope that after my postdoc work, I will be able to pursue my own research projects. 

- What are your main interests outside science?

I love music, and like to explore different music genres. I also enjoy reading classic detective novels. Other than that, I like cooking and baking and, of course, hiking (it’s Bergen!)