Biology subjects

Placzek, M.

Publications and source records attributed to Placzek, M..

9 recordsLinked to original sources

bioRxiv2026

Transforming avian to mammalian modes of digit patterning

How a conserved embryonic organiser--the Sonic hedgehog (Shh)-expressing Zone of Polarising Activity (ZPA)--generates diverse limb architectures in amniotes remains a central problem in evolutionary and developmental biology. The principal difference across species lies in the number of digits produced from ZPA tissue: two in mammals1, one in the chick leg2 and none in the chick wing2. Here we show that this divergence is governed by a Shh-p27Kip1 pathway operating in avian, but not mammalian ZPAs. In chick wing ZPA explants, attenuation of this pathway reveals an intrinsic digit-forming programme, enabling cells to self-organise signalling networks and generate digits after grafting into a host wing bud. Guided by these findings, we redirected the chick leg, which retains stem amniote digit identities, to follow a mammalian-like developmental trajectory. Precise temporal restriction of Shh signalling transforms chick legs into pentadactyl limbs with digit identities characteristic of mammals and their therapsid ancestors, with two digits arising from the ZPA. These findings establish a unifying framework for how Shh controls both digit number and identity across amniotes.

developmental biology↗

bioRxiv2025

Resolving forebrain developmental organisation by analysis of differential growth patterns

The forebrain is the most complex region of the vertebrate CNS, and its developmental organisation is controversial. We fate-mapped the embryonic chick forebrain using lipophilic dyes and Cre-recombination lineage tracing, and built a 4D model of brain growth. We reveal modular patterns of anisotropic growth, ascribed to progenitor regions through multiplex HCR. Morphogenesis is dominated by directional growth towards the eye, more isometric expansion of the prethalamus and dorsal telencephalon, and anterior movement of ventral cells into the hypothalamus. Fate conversion experiments in chick and comparative gene expression analysis in chick and mouse support placement of the hypothalamus ventral to structures extending from the telencephalon up to and including the zona limitans intrathalamica (ZLI), with the dorsoventral axis becoming distorted at the base of the ZLI. Our findings challenge the widely accepted prosomere model of forebrain organisation, and we propose an alternative tripartite hypothalamus model.

developmental biology↗

bioRxiv2022

A neuroepithelial wave of BMP signalling drives anteroposterior specification of the tuberal hypothalamus

The tuberal hypothalamus houses several major hypothalamic nuclei, dozens of transcriptionally distinct cell types, and clinically relevant cell populations implicated in obesity and related metabolic disorders. Building on recent advances in the field, here we draw upon transcriptional, signalling, and fate mapping analyses of chicken embryos and neuroepithelial explants to analyze tuberal hypothalamic development. We show that a wave of BMP signalling sweeps through early floor plate-like progenitors overlying prospective Rathkes pouch as they track anteriorly. The timing of BMP signalling correlates with cell fate, with anterior tuberal specification complete by Hamilton-Hamburger (HH) stage 10 but posterior tuberal progenitors requiring BMPs after this point. scRNA-Seq profiling of FGF10-expressing cells, a proxy for cells with active BMP signalling, through HH8-21 reveals transcriptional differences that may underlie their differing response to BMPs, and the switch from neuroepithelial progenitors to stem-like radial glial cells. This study provides an integrated account of the development of the tuberal hypothalamus.

developmental biology↗

bioRxiv2022

Bespoke data augmentation and network construction enable image classification on small microscopy datasets

Recent work has indicated a need for increased temporal resolution for studies of the early chick brain. Over a 10-hour period, the developmental potential of progenitor cells in the HH10 brain changes, and concomitantly, the brain undergoes subtle changes in morphology. We asked if we could train a deep convolutional neural network to sub-stage HH10 brains from a small dataset (<200 images). By augmenting our images with a combination of biologically informed transformations and data-driven preprocessing steps, we successfully trained a classifier to sub-stage HH10 brains to 87.1% test accuracy. To determine whether our classifier could be generally applied, we re-trained it using images (<250) of randomised control and experimental chick wings, and obtained similarly high test accuracy (86.1%). Saliency analyses revealed that biologically relevant features are used for classification. Our strategy enables training of image classifiers for various applications in developmental biology with limited microscopy data. SUMMARY STATEMENTWe train a deep convolutional network that can be generally applied to accurately classify chick embryos from images. Saliency analyses show that classification is based on biologically relevant features.

developmental biology↗

bioRxiv2021

The neural cell adhesion molecule NrCAM regulates development of hypothalamic tanycytes

Hypothalamic tanycytes are neural stem and progenitor cells, but little is known of how they are regulated. Here we provide evidence that the cell adhesion molecule, NrCAM, regulates tanycytes in the adult niche. NrCAM is strongly expressed in adult mouse tanycytes. Immunohistochemical and in situ hybridization analysis revealed that NrCAM loss of function leads to both a reduced number of tanycytes and reduced expression of tanycyte-specific cell markers, along with a small reduction in tyrosine hydroxylase-positive arcuate neurons. Similar analyses of NrCAM mutants at E16 identify few changes in gene expression or cell composition, indicating that NrCAM regulates tanycytes, rather than early embryonic hypothalamic development. Neurosphere and organotypic assays support the idea that NrCAM governs cellular homeostasis. Single-cell RNA sequencing (scRNA-Seq) shows that tanycyte-specific genes, including a number that are implicated in thyroid hormone metabolism, show reduced expression in the mutant mouse. However, the mild tanycyte depletion and loss of markers observed in NrCAM-deficient mice were associated with only a subtle metabolic phenotype.

neuroscience↗

bioRxiv2021

Single-cell analysis of early chick hypothalamic development reveals that hypothalamic cells are induced from prethalamic-like progenitors.

The hypothalamus is an evolutionarily ancient brain region that regulates many innate behaviors, but its development is still poorly understood. To identify molecular mechanisms controlling hypothalamic specification and patterning, we used single-cell RNA-Seq to profile multiple stages of early hypothalamic development in the chick. We observe that hypothalamic neuroepithelial cells are initially induced from prethalamic-like cells. Two distinct hypothalamic progenitor populations emerge later, which give rise to paraventricular/mammillary and tuberal hypothalamus. At later developmental stages, the regional organization of the chick and mouse hypothalamus closely resembles one another. This study identifies selective markers for major subdivisions of the developing chick hypothalamus and many uncharacterized candidate regulators of hypothalamic patterning and neurogenesis. As proof of concept for the power of the dataset, we demonstrate that follistatin, a novel prethalamic progenitor-like marker, inhibits hypothalamic induction. This study both clarifies the organization of the early developing hypothalamus and identifies novel molecular mechanisms controlling hypothalamic induction, regionalization, and neurogenesis. HighlightsO_LIEarly hypothalamic development was profiled in chick using scRNA-Seq and multiplexed HCR. C_LIO_LIHypothalamic cells are induced from prethalamic-like neuroepithelial cells. C_LIO_LIDistinct paraventricular/mammillary and tuberal progenitor populations emerge later, and hypothalamic organization is evolutionarily conserved. C_LIO_LIPrethalamic progenitor-derived follistatin inhibits hypothalamic specification. C_LI Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=200 SRC="FIGDIR/small/438683v1_ufig1.gif" ALT="Figure 1"> View larger version (73K): org.highwire.dtl.DTLVardef@18ac4c2org.highwire.dtl.DTLVardef@17bb90aorg.highwire.dtl.DTLVardef@1b17cceorg.highwire.dtl.DTLVardef@178e769_HPS_FORMAT_FIGEXP M_FIG C_FIG

developmental biology↗

bioRxiv2020

Defining the signalling determinants of a posterior ventral spinal cord identity in human neuromesodermal progenitor derivatives

The anteroposterior axial identity of motor neurons (MNs) determines their functionality and vulnerability to neurodegeneration. Thus it is a critical parameter in the design of strategies aiming to produce MNs from human pluripotent stem cells (hPSCs) for regenerative medicine and disease modelling applications. However, the in vitro generation of posterior spinal cord MNs has been challenging. Although the induction of cells resembling neuromesodermal progenitors (NMPs), the bona fide precursors of the mammalian spinal cord, offers a promising solution, the progressive specification of posterior MNs from these cells is not well-defined. Here we determine the signals guiding the transition of human NMP-like cells toward posterior ventral spinal cord neurectoderm. We show that combined WNT-FGF activities drive a posterior dorsal early neural state while suppression of TGFβ-BMP signalling pathways, combined with SHH stimulation, promotes a ventral identity. Based on these results, we define an optimised protocol for the generation of posterior MNs that can efficiently integrate within the neural tube of chick embryos. We expect that our findings will facilitate the functional comparison of hPSC-derived spinal cord cells of distinct axial identities.Competing Interest StatementThe authors have declared no competing interest.View Full Text

developmental biology↗

bioRxiv2019

Crumbs 2 mediates ventricular layer remodelling to form the adult spinal cord central canal

In the spinal cord, the adult central canal forms through a poorly-understood process termed dorsal collapse that involves attrition and remodelling of the pseudostratified dorsal ventricular layer. Here we show, in mouse, that dorsal ventricular layer cells adjacent to midline Nestin(+) radial glia downregulate the apical polarity proteins Crumbs2 (CRB2) and aPKC and delaminate in a step-wise manner; concomitantly, Nestin(+) radial glial end-feet ratchet down, to repeat this process. Nestin(+) radial glia secrete a factor that promotes cell delamination. This activity is mimicked by a secreted variant of CRB2 (CRB2S), which is specifically expressed by dorsal midline Nestin(+) radial glia. In cultured cells, CRB2S associated with apical membranes and decreased cell cohesion. Analysis of Crb2F/F/Nestin-Cre+/- mice further confirmed an essential role for CRB2 in dorsal collapse. We propose a model in which CRB2S promotes the progressive attrition of the ventricular layer without loss of overall integrity. This novel mechanism may operate more widely to promote orderly progenitor delamination.

developmental biology↗

bioRxiv2019

Regulation of neuron-specific gene transcription by stress hormone signalling requires synaptic activity in zebrafish

The Glucocorticoid Receptor (GR) co-ordinates metabolic and behavioural responses to stressors. We hypothesised that GR influences behaviour by modulating specific epigenetic and transcriptional processes in the brain. Using the zebrafish as a model organism, the brain methylomes of wild-type and grs357 mutant adults were analysed and GR-sensitive, differentially methylated regions (GR-DMRs) were identified. Two genes with GR-DMRs exhibited distinct methylation and transcriptional sensitivities to GR: the widely expressed direct GR target fkbp5 and neuron-specific aplp1. In larvae, neural activity is required for GR-mediated transcription of aplp1, but not for that of fkbp5. GR regulates metabotropic glutamate receptor gene expression, the activities of which also modulated aplp1 expression, implicating synaptic neurotransmission as an effector of GR function upstream of aplp1. Our results identify two distinct routes of GR-regulated transcription in the brain, including a pathway through which GR couples endocrine signalling to synaptic activity-regulated transcription by modulating metabotropic glutamate receptor expression.

developmental biology↗