Dissecting signaling hierarchies in the patterning of the mouse primitive streak using micropatterned EpiLC colonies.

Embryo studies have established that the patterning of the mouse gastrula depends on a regulatory network in which the WNT, BMP, and NODAL signaling pathways cooperate, but aspects of their respective contributions remain unclear. Studying their impact on the spatial organization and developmental trajectories of micropatterned epiblast-like cell (EpiLC) colonies, we show that NODAL is required prior to BMP action to establish the mesoderm and endoderm lineages. The presence of BMP then forces NODAL and WNT to support the formation of posterior primitive streak (PS) derivatives, while its absence allows them to promote that of anterior PS derivatives. Also, a Nodal mutation elicits more severe patterning defects in vitro than in the embryo, suggesting that ligands of extra-embryonic origin can rescue them. These results support the implication of a combinatorial process in PS patterning and illustrate how the study of micropatterned EpiLC colonies can complement that of embryos.

Differentiation of EpiLCs on Micropatterned Substrates Generated by Micro-Contact Printing.

During the last decades, signaling pathways responsible for the initiation of gastrulation in mammalian embryos have been identified. However, the physical rules governing the tissue spatial patterning and the extensive morphogenetic movements occurring during that process are still elusive. Progress on these issues is slowed by the difficulty to record or perturb the patterning events in real time, especially in mammalian embryos that develop in utero. Because they permit easy observation and manipulation, in vitro model systems offer an exciting opportunity to dissect the rules governing the organization of the mammalian gastrula. For instance, it is sufficient to cultivate human embryonic stem cells on micropatterned substrates to reveal their self-organization potential. We present here a method to obtain micropatterned mouse Epiblast Like Cells colonies, providing a convenient way to compare spatial organization of mouse and human pluripotent stem cells and to complement the characterization of mutant embryos in a controlled environment.

HSPCs display within-family homogeneity in differentiation and proliferation despite population heterogeneity.

High-throughput single-cell methods have uncovered substantial heterogeneity in the pool of hematopoietic stem and progenitor cells (HSPCs), but how much instruction is inherited by offspring from their heterogeneous ancestors remains unanswered. Using a method that enables simultaneous determination of common ancestor, division number, and differentiation status of a large collection of single cells, our data revealed that murine cells that derived from a common ancestor had significant similarities in their division progression and differentiation outcomes. Although each family diversifies, the overall collection of cell types observed is composed of homogeneous families. Heterogeneity between families could be explained, in part, by differences in ancestral expression of cell surface markers. Our analyses demonstrate that fate decisions of cells are largely inherited from ancestor cells, indicating the importance of common ancestor effects. These results may have ramifications for bone marrow transplantation and leukemia, where substantial heterogeneity in HSPC behavior is observed.

First evidence of European eels exiting the Mediterranean Sea during their spawning migration.

The migration route and the spawning site of the European eel Anguilla anguilla are still uncertain. It has been suggested that the Mediterranean eel stock does not contribute to spawning because there is no evidence of eels leaving the Mediterranean Sea. To test this hypothesis, we equipped eight female silver eels from the south of France with pop-up satellite tags during escapement from coastal waters. Once in deeper water, the eels quickly established diel vertical migration (DVM) between the upper and lower mesopelagic zone. Five tagged eels were taken by predators within the Mediterranean, but two eels reached the Atlantic Ocean after six months and at distances greater than 2000 km from release. These eels ceased their DVM while they negotiated the Gibraltar Strait, and remained in deep water until they reached the Atlantic Ocean, when they recommenced DVM. Our results are the first to show that eels from Mediterranean can cross the Strait of Gibraltar and continue their migration into the Atlantic Ocean. This finding suggests that Mediterranean countries, as for other EU states, have an important role to play in contributing to conservation efforts for the recovery of the European eel stock.

Individual and combined effects of copper and parasitism on osmoregulation in the European eel Anguilla anguilla.

The European eel (Anguilla anguilla), a catadromous species, breeds in the sea and migrates to estuarine, lagoon or freshwater habitats for growth and development. Yellow eels, exposed to low or fluctuating salinities, are also exposed to multiple other stressors as pollution, over-fishing and parasitism, which contribute to the dramatic decrease of eel populations in several European countries. The objective of this study was to evaluate the single and combined effects of waterborne copper and experimental infestation of eels with the nematode Anguillicoloides crassus after a salinity challenge from nearly isotonic (18ppt) to hypo- (5ppt) and hypertonic (29ppt) conditions, in order to investigate the osmoregulatory capacity of eels exposed to these stressors. In a nearly isotonic condition (18ppt), blood osmolality remained constant over the 6 weeks contamination to Cu(2+) and Anguillicoloides crassus. In fish exposed to a salinity challenge of 29ppt for 2 weeks, no significant effect was recorded in blood osmolality, Na(+)/K(+)-ATPase (NKA) activity, Na(+) and Cl(-) concentrations. After 2 weeks at 5ppt however, a significant blood osmolality decrease was detected in fish exposed to Anguillicoloides crassus infestation with or without Cu(2+) addition. This decrease may originate from lower Cl(-) levels measured in eels exposed to both stressors. Blood Na(+) levels remained relatively stable in all tested animals, but gill NKA activities were lower in eels exposed to combined stress. No apparent branchial lesions were detected following the different treatments and immunolocalization of NKA revealed well-differentiated ionocytes. Thus, the 5ppt challenge in eels exposed to copper and Anguillicoloides crassus seems to clearly enhance iono/osmoregulatory disturbances. Funded by ANR CES/CIEL 2008-12.

Dynamic expression of immune response genes in the sea bass, Dicentrarchus labrax, experimentally infected with the monogenean Diplectanum aequans.

The sea bass, Dicentrarchus labrax, is one of the most extensively farmed marine fishes in the Mediterranean. Under the high-density condition common in aquaculture, the monogenean gill parasite Diplectanum aequans can cause significant economic losses. This study used real-time quantitative PCR to investigate the dynamic expression of immune response genes in sea bass infected with Diplectanum aequans. The target genes, interleukin-1 (IL-1beta, transforming growth factor (TGF-beta and T-cell receptor (TCR-beta), were studied in the gills and spleen of the sea bass from the first day of infection until thirty days post- infection. Our results showed that there was an increase in IL-1beta gene expression in the spleen and gills and in TGF-beta gene expression in the gills of infected fish. These results show that parasitic infection induced a local inflammatory reaction and that reaction was restricted to the site of infection. Finally, the absence of relationship between TCR-beta expression and the parasitic infection suggests that the adaptive immune system is not involved in the response against this parasite.