Biology subjects

Nemashkalo, A.

Publications and source records attributed to Nemashkalo, A..

3 recordsLinked to original sources

bioRxiv2025

Juxtaposition of human pluripotent stem cells with amnion-like cells is sufficient to trigger primitive streak formation

Studies in the mouse have established that communication between the trophectoderm and the epiblast is crucial for initiating gastrulation. In the primate embryo, the amnion rather than the trophectoderm is directly juxtaposed to the epiblast and may play this role. To model the interactions between the amnion and epiblast, we differentiated human pluripotent stem cells (hPSCs) to amnion-like cells (AMLCs) and juxtaposed them in a controlled manner with undifferentiated hPSCs, which represent the epiblast. We found that juxtaposition between these cell types is sufficient to initiate a range of cell behaviors associated with gastrulation including organized differentiation to primitive streak and downstream mesendodermal cell fates and directed cell migration out of the primitive streak region. Performing knockout experiments specifically in either the epiblast or amnion compartment revealed intricate crosstalk that is required to properly initiate gastrulation. In particularly, using knockouts of NODAL we show that Nodal signaling in both the amnion and epiblast is required for gastrulation patterning. Finally, we show that inductive ability is a transient property acquired during amnion differentiation, and that cells that differentiate from this inductive state acquire an extraembryonic mesenchyme identity. This study establishes a system to study epiblast-amnion communication and shows that this communication is sufficient to initiate gastrulation in the epiblast.

developmental biology↗

bioRxiv2021

Nodal is a short-range morphogen with activity that spreads through a relay mechanism in human gastruloids

Morphogens are signaling molecules that convey positional information and dictate cell fates during development. Little is known about how morphogen gradients are created and interpreted during mammalian embryogenesis. Here we take advantage of a human gastruloid model to visualize endogenous Nodal protein in living cells. We show that Nodal is extremely short range so that Nodal protein is limited to the immediate neighborhood of source cells. Nodal activity spreads through a relay mechanism in which Nodal production induces neighboring cells to transcribe Nodal. We further show that the Nodal inhibitor Lefty, while biochemically capable of long-range diffusion, also acts locally to control the timing of Nodal spread and therefore of mesoderm differentiation during patterning. Our study establishes a novel paradigm for tissue patterning by an activator-inhibitor pair.

developmental biology↗

bioRxiv2017

Morphogen And Community Effects Determine Cell Fates In Response To BMP4 Signaling In Human Embryonic Stem Cells

Paracrine signals maintain developmental states and create cell-fate patterns in vivo, and influence differentiation outcomes in human embryonic stem cells (hESCs) in vitro. Systematic investigation of morphogen signaling is hampered by the difficulty of disentangling endogenous signaling from experimentally applied ligands. Here, we grow hESCs in micropatterned colonies of 1-8 cells (\"Colonies\") to quantitatively investigate paracrine signaling and the response to external stimuli. We examine BMP4-mediated differentiation in Colonies and standard culture conditions and find that in Colonies, above a threshold concentration, BMP4 gives rise to only a single cell fate, contrary to its role as a morphogen in other developmental systems. Under standard culture conditions, BMP4 acts as morphogen, but this effect requires secondary signals and particular cell densities. We further find that a \"community effect\" enforces a common fate within Colonies both in the state of pluripotency and when cells are differentiated, and that this effect allows more precise response to external signals. Using live cell imaging to correlate signaling histories with cell fates, we demonstrate that interactions between neighbors result in sustained, homogenous signaling necessary for differentiation.\n\nSummary StatementWe quantitatively examined signaling and differentiation in hESC colonies of varying size treated with BMP4. We show that secondary signals result in morphogen and community effects that determine cell fates.

developmental biology↗