Our brains are asymmetric but does this matter for effective cognitive function?
Elena Dreosti, Steve Wilson and colleagues think it does.
By imaging activity of individual neurons in larval zebrafish they found a region of the brain in which most neurons responding to a light stimulus were on the left whereas most responding to odour were on the right (Figure 1). In brains that were symmetric with either double-left or double-right character, they observed that responses to odour or to light were almost absent. These results show that loss of brain asymmetry can have significant consequences upon sensory processing and circuit function and raises the possibility that defects in the establishment of brain lateralization could be causative of cognitive or other symptoms of brain dysfunction.
Figure 1. Examples of neuronal activity in the left and right habenular nuclei (L Hb and R Hb) of four different four-day old fish with normal left-right habenular laterality (LR), reversed laterality (RL), symmetric double-right (RR) and symmetric double-left (LL) habenulae showing lateralization of neuronal responses to light and odour. Neuronal cell bodies are shown as dots colour-coded in red, blue, violet, or white depending on whether they responded to light, odour, both light and odour, or were non-responding.
Original article: Dreosti E., Llopis, N., Carl M., Yaksi E. & Wilson S.W. (2013) Left-right asymmetry is required for the habenulae to respond to both visual and olfactory stimuli. Current Biology http://dx.doi.org/10.1016/j.cub.2014.01.016
Despite looking nothing like brain tissue, our eyes initially form as outgrowths from the brain
during embryonic development. New research from Kenzo Ivanovitch, Florencia Cavodeassi and
Stephen Wilson has revealed how prospective eye cells initiate their journey from the brain to the
eye sockets. They reasoned that two criteria must be met for successful outgrowth of the eyes:
first, eye forming cells must initiate a behavioural programme distinct from adjacent territories in
the brain; and second, that future eye cells must not intermix with other brain cells. To investigate
these issues, the UCL researchers used very high-resolution microscopy to resolve the behaviours
of individual eye forming cells in transparent zebrafish embryos that are eminently well-suited for
such imaging analyses. They discovered that the eye-forming cells precociously organise as a
polarised sheet of cells (an epithelium) when compared to cells in neighbouring brain regions, and
that this behaviour is essential for the proper evagination of the primordia of the eyes. They further
unravelled a molecular mechanism that ensures that the eye-forming cells are prevented from
intermixing with adjacent brain cells as the eyes begin to take shape. This work is paving the way
for a better understanding of eye morphogenesis and organogenesis and is published in papers in
the journals Development and Developmental Cell.
Figure 1. Image of a head-on view of the brain of a zebrafish embryo just as the prospective eye cells (green) start to push out laterally to form the optic vesicles. The orange labelling is Laminin, a protein present at the outer surface of the eye cells that is necessary for proper outgrowth.
Figure 2. Sequential images from a movie in which prospective eye cells (green) reorganise and move outwards from the brain to form the nascent eyes (optic vesicles).
Movie 1. Time-lapse movie of prospective eye cells bulging out from the brain (including telencephalon and hypothalamus) to form the nascent eyes (optic vesicles). The membranes of the cells are labelled green and the cell nuclei in red.
Cavodeassi, Ivanovitch and Wilson (2013). Eph/Ephrin signalling maintains eye field segregation from adjacent neural plate territories during forebrain morphogenesis. Development, 140:4193-202.
Ivanovitch, Cavodeassi and Wilson (2013). Precocious acquisition of neuroepithelial character in the eye field underlies the onset of eye morphogenesis. Developmental Cell, 27:293-305.
Ana, Ricardo and Kate have organised a course on “Cell Biology in the Zebrafish Lab’ for the Year 12 UCL Summer Challenge. The aim of the UCL Summer Challenge is to increase access to UCL for students from under-represented backgrounds by helping them to develop their independent research, critical thinking, academic writing and presentation skills. The course was fully booked up, and the students have been getting hands on experience in zebrafish research, learning about brain development, sleep and behaviour and looking at some of our mutant and transgenic lines.
Dr Jason Rihel discusses the biological significance of zebrafish on BBC Radio4′s Material World Program (April 18th) along with Dr. Stemple from the Sanger Institute.
Why is the zebrafish so important for genetic research?
“It’s a compromise between having the complexity to model some of the things that we want to study – brain function, behaviour, … – but also the simplicity that we might be able to understand it.” said Dr Jason Rihel (UCL Cell & Developmental Biology). Listen here from 11 mins (to download right click and “save target as/link as”).
Dr Masa Tada has been awarded a 5-year Cancer Research UK-funded programme grant, jointly with Paul Martin at the University of Bristol, to study the earliest interactions of host with pre-neoplastic cells in Zebrafish. This programme of projects investigates how epithelia can extrude pre-neoplastic cells (Tada Lab) and how the host innate immune system interacts in positive and negative ways with these cells (Martin Lab). A post-doc position is available in Tada Lab. Please contact Masa for details.
The Wilson lab’s Kate and Tom discuss why the zebrafish is a beautiful organism to work on in this short film by the Wellcome Trust.
Morphogenesis underlying the development of the everted teleost telencephalon.
Monica Folgeira, Steve Wilson and John Clarke
Brain diversity has puzzled scientists for centuries. But, what do we mean by “brain diversity”? If one compares brains from many different species of vertebrates, soon one realizes how different they look. This diversity in brain form or morphology is extraordinary not only for brains from very separate groups (e. g. mammals vs. fishes), but also within the same group.
Take as an example “ray-finned fishes”, a group of fishes with more than 30,000 species and whose members have fins supported by bony spines. Within this group, brain morphology can be very different even between closely related species. In order to understand how brain diversity is generated, we studied in detail the development of the telencephalon of the zebrafish (a ray-finned fish).
For full details see publication summary.
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