The lateral-line system comprises a large set of individual organs, the neuromasts, distributed over the head and body in species-specific patterns

Alain Ghysen - Montpellier

the lateral line: a sensory system of utmost importanceprovides a sense of "touch at a distance" (touch without touching)

involved in:

- predator avoidance- prey detection- swimming in schools- rheotaxis (swim against current)- sexual behaviour- building map of external world- and probably more…

neuromast : cellular organization

DiAsp (fluorescent dye specifically taken up by functional hair cells,works only on living fish)

Nomarski optics

tuft of hairs

round nucleiof hair cells

elongated nucleiof mantle cells

Alc. Phosphatase(reveals the polarity of the neuromast, works on fixed fish)

Various methods to detect neuromasts in zebrafish

will they all work in tunafish embryos & larvae?

hair cells

neurons

mantle cells

support cells

skin

Many different patterns in adult fish

what is the pattern in adult zebrafish?

complicated pattern with several hundreds of neuromasts(marked with Di Asp, every white dot is a neuromast)

In the embryo: much simpler pattern 5 neuromasts on each side of the body

Danio: ostariophysian, basal group; Psetta: acanthopterygian, highly derived groupdiverged about 150 million years ago

=> embryonic patterns are highly conserved even though adult patterns very different (so highly conserved that the tunafish embryonic pattern is likely to be the same - verify…)

Psetta maxima (turbot) embryo: almost identical to zebrafish

How is the embryonic pattern formed? understood only in zebrafish

(optional: simplified phylogeny)

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The embryonic pattern is laid down by a migrating group of cells (migrating primordium). This primordium deposits five groups of cells, each of which will become a neuromast

the migration pathway of the primordium

(unrelated to SELFDOTT, but interesting anyway: the molecular machinery that underlies primordium migration is exactly the same as that which underlies cell migration and the formation of metastases in many human cancers)

primordium migration

Transition from embryonic (highly conserved) to adult (highly divergent) pattern?

in Danio: 1. Formation of a second lateral line (in blue) with a lateral and a dorsal branch

2. Formation of intercalary neuromasts between L1 - L5

L1 L2 L3 L4 L5

nothing is known about post-embryonic development in any other fish species…

=> a very simple and sensitive way to measure growth?

Potential interest for SELFDOTT: in zebrafish, the post-embryonic growth of the PLL system has a very reproducible dynamics

Number of post-embryonic neuromasts

Project:

- develop tools to visualize neuromasts at different developmental stages

- verify that the "standard" embryonic pattern is conserved in BFT

- explore the onset of post-embryonic development

- establish the dynamics of neuromast addition (to validate PLL as a quantitative indicator of development)

- Brain projections: I will introduce this aspect next year as there is no way I could do this in the 10min period that is allowed to me by Denis Coves