3D reconstruction of a gastrulating human embryo.

Progress in understanding early human development has been impeded by the scarcity of reference datasets from natural embryos, particularly those with spatial information during crucial stages like gastrulation. We conducted high-resolution spatial transcriptomics profiling on 38,562 spots from 62 transverse sections of an intact Carnegie stage (CS) 8 human embryo. From this spatial transcriptomic dataset, we constructed a 3D model of the CS8 embryo, in which a range of cell subtypes are identified, based on gene expression patterns and positional register, along the anterior-posterior, medial-lateral, and dorsal-ventral axis in the embryo. We further characterized the lineage trajectories of embryonic and extra-embryonic tissues and associated regulons and the regionalization of signaling centers and signaling activities that underpin lineage progression and tissue patterning during gastrulation. Collectively, the findings of this study provide insights into gastrulation and post-gastrulation development of the human embryo.

Cytoneme-mediated transport of active Wnt5b-Ror2 complexes in zebrafish.

Chemical signalling is the primary means by which cells communicate in the embryo. The underlying principle refers to a group of ligand-producing cells and a group of cells that respond to this signal because they express the appropriate receptors1,2. In the zebrafish embryo, Wnt5b binds to the receptor Ror2 to trigger the Wnt-planar cell polarity (PCP) signalling pathway to regulate tissue polarity and cell migration3,4. However, it remains unclear how this lipophilic ligand is transported from the source cells through the aqueous extracellular space to the target tissue. In this study, we provide evidence that Wnt5b, together with Ror2, is loaded on long protrusions called cytonemes. Our data further suggest that the active Wnt5b-Ror2 complexes form in the producing cell and are handed over from these cytonemes to the receiving cell. Then, the receiving cell has the capacity to initiate Wnt-PCP signalling, irrespective of its functional Ror2 receptor status. On the tissue level, we further show that cytoneme-dependent spreading of active Wnt5b-Ror2 affects convergence and extension in the zebrafish gastrula. We suggest that cytoneme-mediated transfer of ligand-receptor complexes is a vital mechanism for paracrine signalling. This may prompt a reevaluation of the conventional concept of characterizing responsive and non-responsive tissues solely on the basis of the expression of receptors.

A single-cell time-lapse of mouse prenatal development from gastrula to birth.

The house mouse (Mus musculus) is an exceptional model system, combining genetic tractability with close evolutionary affinity to humans1,2. Mouse gestation lasts only 3 weeks, during which the genome orchestrates the astonishing transformation of a single-cell zygote into a free-living pup composed of more than 500 million cells. Here, to establish a global framework for exploring mammalian development, we applied optimized single-cell combinatorial indexing3 to profile the transcriptional states of 12.4 million nuclei from 83 embryos, precisely staged at 2- to 6-hour intervals spanning late gastrulation (embryonic day 8) to birth (postnatal day 0). From these data, we annotate hundreds of cell types and explore the ontogenesis of the posterior embryo during somitogenesis and of kidney, mesenchyme, retina and early neurons. We leverage the temporal resolution and sampling depth of these whole-embryo snapshots, together with published data4-8 from earlier timepoints, to construct a rooted tree of cell-type relationships that spans the entirety of prenatal development, from zygote to birth. Throughout this tree, we systematically nominate genes encoding transcription factors and other proteins as candidate drivers of the in vivo differentiation of hundreds of cell types. Remarkably, the most marked temporal shifts in cell states are observed within one hour of birth and presumably underlie the massive physiological adaptations that must accompany the successful transition of a mammalian fetus to life outside the womb.

Coupling and uncoupling of midline morphogenesis and cell flow in amniote gastrulation.

Large-scale cell flow characterizes gastrulation in animal development. In amniote gastrulation, particularly in avian gastrula, a bilateral vortex-like counter-rotating cell flow, called 'polonaise movements', appears along the midline. Here, through experimental manipulations, we addressed relationships between the polonaise movements and morphogenesis of the primitive streak, the earliest midline structure in amniotes. Suppression of the Wnt/planar cell polarity (PCP) signaling pathway maintains the polonaise movements along a deformed primitive streak. Mitotic arrest leads to diminished extension and development of the primitive streak and maintains the early phase of the polonaise movements. Ectopically induced Vg1, an axis-inducing morphogen, generates the polonaise movements, aligned to the induced midline, but disturbs the stereotypical cell flow pattern at the authentic midline. Despite the altered cell flow, induction and extension of the primitive streak are preserved along both authentic and induced midlines. Finally, we show that ectopic axis-inducing morphogen, Vg1, is capable of initiating the polonaise movements without concomitant PS extension under mitotic arrest conditions. These results are consistent with a model wherein primitive streak morphogenesis is required for the maintenance of the polonaise movements, but the polonaise movements are not necessarily responsible for primitive streak morphogenesis. Our data describe a previously undefined relationship between the large-scale cell flow and midline morphogenesis in gastrulation.

Desarrollo embrionario del pargo colorado Lutjanus colorado (Jordan & Gilbert, 1882) / Embryonic development of pargo colorado Lutjanus colorado (Jordan & Gilbert, 1882)

El pargo colorado (Lutjanus colorado) es una especie con un alto valor comercial en el mercado mexicano, con potencial para su cultivo. Hasta la fecha no existen estudios sobre su reproducción, cultivo larvario y engorda en cautiverio. El presente trabajo es el primer reporte sobre la descripción a detalle del desarrollo embrionario de la especie bajo condiciones de cultivo. Los huevos fertilizados viables del pargo colorado son pelágicos, esféricos, transparentes y con una sola gota de aceite. Midieron 0,77±0,09 mm de diámetro y la gota de aceite 0,14±0,01 mm. La primera división ocurrió a las 0,05 horas post fertilización (HPF). La eclosión se llevó a cabo a las 17,22 HPF bajo las condiciones del presente estudio. Las larvas recién eclosionadas midieron 1,8±0,1 mm de longitud total (LT). El desarrollo embrionario de esta especie fue similar a la descrita para especies de la misma familia. Los resultados del presente estudio aportan información básica para iniciar el desarrollo de la biotecnología para la producción de semilla de esta especie a escala comercial.

The Colorado snapper (Lutjanus colorado) is one of the most commercially important fish species in México and it is considered a suitable candidate for culture. Until now, no research has been carried out on its reproduction, larviculture and fattening in captivity. This study is the first description of embryonic development of this species under controlled conditions. Fertilized eggs of Colorado snapper are pelagic, spherical and transparent and contain one drop of oil. Eggs measured 0.77±0.09 mm and the drop of oil 0.14±0.01 mm. First cell division occurred at 0.05 h post-fertilization (HPF), hatching at 17.22 HPF under the above described conditions. Larvae total length (LT) was 1.8±0.1 mm. Embryonic development of this species was similar to other lutjanidae species. These results provide basic information for developing the necessary biotechnology for commercial seed production of the Colorado snapper.