Trunk-like Structures Research Articles

Self-organizing models of human trunk organogenesis recapitulate spinal cord and spine co-morphogenesis.

Integrated in vitro models of human organogenesis are needed to elucidate the multi-systemic events underlying development and disease. Here we report the generation of human trunk-like structures that model the co-morphogenesis, patterning and differentiation of the human spine and spinal cord. We identified differentiation conditions for human pluripotent stem cells favoring the formation of an embryo-like extending antero-posterior (AP) axis. Single-cell and spatial transcriptomics show that somitic and spinal cord differentiation trajectories organize along this axis and can self-assemble into a neural tube surrounded by somites upon extracellular matrix addition. Morphogenesis is coupled with AP patterning mechanisms, which results, at later stages of organogenesis, in in vivo-like arrays of neural subtypes along a neural tube surrounded by spine and muscle progenitors contacted by neuronal projections. This integrated system of trunk development indicates that in vivo-like multi-tissue co-morphogenesis and topographic organization of terminal cell types can be achieved in human organoids, opening windows for the development of more complex models of organogenesis.

In preprints: improving and interrogating embryo models.

In preprints: improving and interrogating embryo models.

Generation of Mouse Pluripotent Stem Cell-derived Trunk-like Structures: An in vitro Model of Post-implantation Embryogenesis.

Post-implantation mammalian embryogenesis involves profound molecular, cellular, and morphogenetic changes. The study of these highly dynamic processes is complicated by the limited accessibility of in utero development. In recent years, several complementary in vitro systems comprising self-organized assemblies of mouse embryonic stem cells, such as gastruloids, have been reported. We recently demonstrated that the morphogenetic potential of gastruloids can be further unlocked by the addition of a low percentage of Matrigel as an extracellular matrix surrogate. This resulted in the formation of highly organized trunk-like structures (TLSs) with a neural tube that is frequently flanked by bilateral somites. Notably, development at the molecular and morphogenetic levels is highly reminiscent of the natural embryo. To facilitate access to this powerful model, here we provide a detailed step-by-step protocol that should allow any lab with access to standard cell culture techniques to implement the culture system. This will provide the user with a means to investigate early mid-gestational mouse embryogenesis at an unprecedented spatiotemporal resolution.

Modeling mammalian trunk development in a dish

Mammalian post-implantation development comprises the coordination of complex lineage decisions and morphogenetic processes shaping the embryo. Despite technological advances, a comprehensive understanding of the dynamics of these processes and of the self-organization capabilities of stem cells and their descendants remains elusive. Building synthetic embryo-like structures from pluripotent embryonic stem cells in vitro promises to fill these knowledge gaps and thereby may prove transformative for developmental biology. Initial efforts to model the post-implantation embryo resulted in structures with compromised morphology (gastruloids). Recent approaches employing modified culture media, an extracellular matrix surrogate or extra-embryonic stem cells, however, succeeded in establishing embryo-like architecture. For example, embedding of gastruloids in Matrigel unlocked self-organization into trunk-like structures with bilateral somites and a neural tube-like structure, together with gut tissue and primordial germ cell-like cells. In this review, we describe the currently available models, discuss how these can be employed to acquire novel biological insights, and detail the imminent challenges for improving current models by in vitro engineering.

Trunk formation in a dish

Developmental Biology Building mammalian embryos from self-organizing stem cells in culture would accelerate the investigation of morphogenetic and differentiation processes that shape the body plan. Veenvliet et al. report a method for generating embryonic trunk-like structures (TLSs) with a neural tube, somites, and gut by embedding mouse embryonic stem cell aggregates in an extracellular matrix surrogate. Live imaging and comparative single-cell transcriptomics indicate that TLS formation is analogous to mouse development. TLSs therefore provide a scalable, tractable, and accessible high-throughput platform for decoding mammalian embryogenesis at a high level of resolution. Science , this issue p. [eaba4937][1] [1]: /lookup/doi/10.1126/science.aba4937

Mouse embryonic stem cells self-organize into trunk-like structures with neural tube and somites.

Post-implantation embryogenesis is a highly dynamic process comprising multiple lineage decisions and morphogenetic changes that are inaccessible to deep analysis in vivo. We found that pluripotent mouse embryonic stem cells (mESCs) form aggregates that upon embedding in an extracellular matrix compound induce the formation of highly organized "trunk-like structures" (TLSs) comprising the neural tube and somites. Comparative single-cell RNA sequencing analysis confirmed that this process is highly analogous to mouse development and follows the same stepwise gene-regulatory program. Tbx6 knockout TLSs developed additional neural tubes mirroring the embryonic mutant phenotype, and chemical modulation could induce excess somite formation. TLSs thus reveal an advanced level of self-organization and provide a powerful platform for investigating post-implantation embryogenesis in a dish.

Understanding Formation of Young, Distributed Low-mass Stars and Clusters in the W4 Cloud Complex

Abstract It is well known that most of the stars form in rich clusters. However, recent Spitzer observations have shown that a significant number of stars also form in the distributed mode; their origin is not well understood. In this work, we aim to investigate clustered and distributed modes of star formation in the W4 complex. To do so, we identified and characterized the young stellar population associated with the region using homogeneous infrared data sets obtained from the Two Micron All Sky Survey, GLIMPSE, MIPS, and Wide-field Infrared Survey Explorer surveys. We make stellar surface density and minimum spanning tree maps to identify young clusters, and use Spitzer images to identify irradiated structures, such as elephant-trunk-like structures (ETLSs) and pillars in the region. The surface density distribution of the young stellar objects (YSOs) reveals three new clusterings and ∼50% distributed protostars in the H ii region. The clusters are of low-mass nature but significantly younger than the central cluster IC 1805. We identified ∼ 38 ETLSs in the region, a majority of which consist of one or a few stars at their tips. We find that these stars are low-mass (<2 M ⊙) YSOs, located at the outskirts (>17 pc) of the cluster IC 1805 and are part of the scattered distributed population. We argued that the star formation in the ETLSs of W4 is going on possibly due to the triggering effect of the expanding W4 bubble. Although high-resolution photometric and spectroscopic data would be required to confirm the scenario, nonetheless, we discuss the implications of this scenario for our understanding of distributed low-mass star formation in cloud complexes as opposed to other mechanisms such as turbulent fragmentation and dynamical ejection.

WIDE-FIELD INFRARED SURVEY EXPLOREROBSERVATIONS OF THE EVOLUTION OF MASSIVE STAR-FORMING REGIONS

We present the results of a mid-infrared survey of 11 outer Galaxy massive star-forming regions and 3 open clusters with data from the Wide-field Infrared Survey Explorer (WISE). Using a newly developed photometric scheme to identify young stellar objects and exclude extragalactic contamination, we have studied the distribution of young stars within each region. These data tend to support the that latter generations may be triggered by the interaction of winds and radiation from the first burst of massive star formation with the molecular cloud material leftover from that earlier generation of stars. We dub this process the fireworks hypothesis since star formation by this mechanism would proceed rapidly and resemble a burst of fireworks. We have also analyzed small cutout WISE images of the structures around the edges of these massive star-forming regions. We observe large (1-3 pc size) pillar and trunk-like structures of diffuse emission nebulosity tracing excited polycyclic aromatic hydrocarbon molecules and small dust grains at the perimeter of the massive star-forming regions. These structures contain small clusters of emerging Class I and Class II sources, but some are forming only a single to a few new stars.

Stars at the Tip of Peculiar Elephant Trunk-Like Clouds in IC 1848E: A Possible Third Mechanism of Triggered Star Formation

Abstract The H II region IC 1848 harbors a lot of intricate elephant trunk-like structures that look morphologically different from usual bright-rimmed clouds (BRCs). Of particular interest is a concentration of thin and long elephant trunk-like structures in the southeastern part of IC 1848E. Some of them have an apparently associated star or two stars at their very tip. We conducted $VI_{\rm c}$ photometry of several of these stars. Their positions on the $V/(V$$-$$I_{\rm c}$) color–magnitude diagram as well as the physical parameters obtained by SED fittings indicate that they are low-mass pre–main-sequence stars having ages of mostly one Myr, or less. This strongly suggests that they formed from elongated, elephant trunk-like clouds. We presume that such elephant trunk-like structures are genetically different from BRCs, on the basis of the differences in morphology, size distributions, and the ages of the associated young stars. We suspect that those clouds have been caused by hydrodynamical instability of the ionization/shock front of the expanding H II region. Similar structures often show up in recent numerical simulations of the evolution of H II regions. We further hypothesize that this mechanism makes a third mode of triggered star formation associated with H II regions, in addition to the two known mechanisms, i.e., collect-and-collapse of the shell accumulated around an expanding H II region and radiation-driven implosion of BRCs originated from pre-existing cloud clumps.

A model for elemental coronal flux loops

The photosphere possesses many small, intense patches of magnetic flux. Each of these patches (or sources) is connected magnetically through the corona to several sources of opposite polarity. An elemental flux loop consists of all of the flux joining one such source to another. We find that each source is connected to twenty other sources, on average, and that the typical flux and diameter of elemental loops in the corona are 10 16 Mx and 200 km; there are approximately 17 separators for each source. We also model a typical large-scale coronal loop consisting of many elemental loops and determine its complex internal topology. Each upright null lies at the end of about 22 separatrices, which tend to be clustered together in trunk-like structures, analogous to river- valleys in a geographical contour map. Prone nulls correspond to saddle points, while their spines are analogous to watersheds.

HowStrigaParasitizes its Host: a TEM and SEM Study

The cellular contact betweenStriga hermonthicaandStriga asiaticaand their hosts,Zea maysandSorghum bicolor, was investigated by light, transmission electron and scanning electron microscopy. The xylem connections between parasites and hosts involve very specific, clustered intrusions into the host's water conducting elements, predominantly into the large vessel elements. A single haustorial cell can penetrate a host vessel element with more than one intrusion. All intrusions become covered by an additional electron-opaque wall layer. During subsequent differentiation, a dissolution of specific wall parts of the cell intrusions occurs so that open, cup- or trunk-like structures result. The vessel-like host contact can comprise up to five openings within a single intrusion. Concomitantly, the intrusions and the haustorial cells to which they belong lose their protoplasts and transform into elements which take up water. The walls of the haustorial cells and both wall parts of their appendages become strongly lignified. The water and nutrient absorbing structures inserted into the host vessel are named ‘oscula’. Within the whole haustorial complex of bothStrigaspecies no phloem elements were detected. Translocation of substances from host to parasite are briefly discussed.