A dual-fluorescence reporter in the Eomes locus for live imaging and medium-term lineage tracing

Polarity inversion reorganizes the stem cell compartment of the trophoblast lineage

The extra-embryonic tissues that form the placenta originate from a small population of trophectoderm cells with stem cell properties, positioned at the embryonic pole of the mouse blastocyst. During the implantation stages, the polar trophectoderm rapidly proliferates and transforms into extra-embryonic ectoderm. The current model of trophoblast morphogenesis suggests that tissue folding reshapes the trophoblast during the blastocyst to egg cylinder transition. Instead of through folding, here we found that the tissue scale architecture of the stem cell compartment of the trophoblast lineage is reorganized via inversion of the epithelial polarity axis. Our findings show the developmental significance of polarity inversion and provide a framework for the morphogenetic transitions in the peri-implantation trophoblast.

3D biomimetic platform reveals the first interactions of the embryo and the maternal blood vessels

The process of implantation and the cellular interactions at the embryo-maternal interface are intrinsically difficult to analyze, as the implanting embryo is concealed by the uterine tissues. Therefore, the mechanisms mediating the interconnection of the embryo and the mother are poorly understood. Here, we established a 3D biomimetic culture environment that harbors the key features of the murine implantation niche. This culture system enabled direct analysis of trophoblast invasion and revealed the first embryonic interactions with the maternal vasculature. We found that implantation is mediated by the collective migration of penetrating strands of trophoblast giant cells, which acquire the expression of vascular receptors, ligands, and adhesion molecules, assembling a network for communication with the maternal blood vessels. In particular, Pdgf signaling cues promote the establishment of the heterologous contacts. Together, the biomimetic platform and our findings thereof elucidate the hidden dynamics of the early interactions at the implantation site.

The microcephaly gene Donson is essential for progenitors of cortical glutamatergic and GABAergic neurons

Biallelic mutations in DONSON, an essential gene encoding for a replication fork protection factor, were linked to skeletal abnormalities and microcephaly. To better understand DONSON function in corticogenesis, we characterized Donson expression and consequences of conditional Donson deletion in the mouse telencephalon. Donson was widely expressed in the proliferation and differentiation zones of the embryonic dorsal and ventral telencephalon, which was followed by a postnatal expression decrease. Emx1-Cre-mediated Donson deletion in progenitors of cortical glutamatergic neurons caused extensive apoptosis in the early dorsomedial neuroepithelium, thus preventing formation of the neocortex and hippocampus. At the place of the missing lateral neocortex, these mutants exhibited a dorsal extension of an early-generated paleocortex. Targeting cortical neurons at the intermediate progenitor stage using Tbr2-Cre evoked no apparent malformations, whereas Nkx2.1-Cre-mediated Donson deletion in subpallial progenitors ablated 75% of Nkx2.1-derived cortical GABAergic neurons. Thus, the early telencephalic neuroepithelium depends critically on Donson function. Our findings help explain why the neocortex is most severely affected in individuals with DONSON mutations and suggest that DONSON-dependent microcephaly might be associated with so far unrecognized defects in cortical GABAergic neurons. Targeting Donson using an appropriate recombinase is proposed as a feasible strategy to ablate proliferating and nascent cells in experimental research.

The cerebral cortex constitutes the largest part of the mammalian brain and is generated prenatally by highly proliferative progenitors. Genes encoding proteins that are essential for chromosomal segregation, mitotic division, DNA repair, and DNA damage response are frequently mutated in individuals diagnosed with microcephaly, a clinical condition characterized by cerebrocortical hypotrophy. Recent findings suggest that biallelic mutations in DONSON, a replication fork stabilization factor, cause microcephaly and skeletal defects, but this has not been formally tested. Here, we find that Cre-mediated Donson deletion in progenitors of cortical glutamatergic and cortical GABAergic neurons causes extensive programmed cell death at early stages of cortical development in mice. Cell death is induced in the proliferation zones and the postmitotic differentiation zones of the targeted progenitors. Mice undergoing Donson ablation in glutamatergic progenitors do not develop the hippocampus and dorsolateral neocortex, which leads to a dorsal shift of the early-generated piriform cortex. Donson deletion in GABAergic progenitors eliminates the vast majority of GABAergic neurons and oligodendrocyte precursors arising in the targeted lineage. We thus establish that Donson is essential for diverse early telencephalic progenitors. Targeting Donson might be used to kill off highly proliferating cells in experimental and probably therapeutic settings.

Spatiotemporal sequence of mesoderm and endoderm lineage segregation during mouse gastrulation

Anterior mesoderm (AM) and definitive endoderm (DE) progenitors represent the earliest embryonic cell types that are specified during germ layer formation at the primitive streak (PS) of the mouse embryo. Genetic experiments indicate that both lineages segregate from Eomes-expressing progenitors in response to different Nodal signaling levels. However, the precise spatiotemporal pattern of the emergence of these cell types and molecular details of lineage segregation remain unexplored. We combined genetic fate labeling and imaging approaches with single-cell RNA sequencing (scRNA-seq) to follow the transcriptional identities and define lineage trajectories of Eomes-dependent cell types. Accordingly, all cells moving through the PS during the first day of gastrulation express Eomes AM and DE specification occurs before cells leave the PS from Eomes-positive progenitors in a distinct spatiotemporal pattern. ScRNA-seq analysis further suggested the immediate and complete separation of AM and DE lineages from Eomes-expressing cells as last common bipotential progenitor.

Medial Amygdala Kiss1 Neurons Mediate Female Pheromone Stimulation of Luteinizing Hormone in Male Mice

BACKGROUND/AIMS

The medial amygdala (MeA) responds to olfactory stimuli and alters reproductive physiology. However, the neuronal circuit that relays signals from the MeA to the reproductive axis remains poorly defined. This study aimed to test whether MeA kisspeptin (MeAKiss) neurons in male mice are sensitive to sexually relevant olfactory stimuli and transmit signals to alter reproductive physiology. We also investigated whether MeAKiss neurons have the capacity to elaborate glutamate and GABA neurotransmitters and potentially contribute to reproductive axis regulation.

METHODS

Using female urine as a pheromone stimulus, MeAKiss neuronal activity was analysed and serum luteinizing hormone (LH) was measured in male mice. Next, using a chemogenetic approach, MeAKiss neurons were bi-directionally modulated to measure the effect on serum LH and evaluate the activation of the preoptic area. Lastly, using in situ hybridization, we identified the proportion of MeAKiss neurons that express markers for GABAergic (Vgat) and glutamatergic (Vglut2) neurotransmission.

RESULTS

Male mice exposed to female urine showed a two-fold increase in the number of c-Fos-positive MeAKiss neurons concomitant with raised LH. Chemogenetic activation of MeAKiss neurons significantly increased LH in the absence of urine exposure, whereas inhibition of MeAKiss neurons did not alter LH. In situ hybridization revealed that MeAKiss neurons are a mixed neuronal population in which 71% express Vgat mRNA, 29% express Vglut2 mRNA, and 6% express both.

CONCLUSIONS

Our results uncover, for the first time, that MeAKiss neurons process sexually relevant olfactory signals to influence reproductive hormone levels in male mice, likely through a complex interplay of neuropeptide and neurotransmitter signalling.