Helen Willsey is an Associate Professor at the Weill Institute for Neuroscience at the University of California, San Francisco (UCSF), USA. Helen's group uses frog models to dissect how risk genes contribute to psychiatric disorders. We spoke to Helen to learn more about her career trajectory, the importance of mentorship and the value of maintaining a full life both in and out of the lab.

Previous studies from us and others suggest that the second heart field (SHF)-derived outflow tract (OFT) wall can undergo a cell fate transition to mesenchymal cells within the intercalated valve swelling (ICVS). However, the trajectory of this transition and its intrinsic regulation remain unknown. Here, we investigate cell fate determination in OFT development and identify specific Nkx2-5 expression in the inferior midline OFT (imOFT) wall and adjacent ICVS. scRNA-seq of E10.5 OFT revealed a transcriptional signature specific to the imICVS within the heterogeneous cell populations. We observed that cells of the imOFT wall ingress while maintaining myocyte properties, whereas the leading cells initiate a transition to a mesenchymal fate. Furthermore, these ingressing cells exhibit 'lily-bulb' collective cell migration. In addition, we found that β-catenin, Shh and FGF8 signaling are associated with imICVS formation. These results identify a novel type of cell ingression and the imICVS appears to spatially coordinate the distribution of OFT main cushion derived from neural crest. This study provides new insights into the role of the SHF in OFT septation and the pathogenesis of congenital heart diseases.

Auxin, a plant hormone, is crucial for organ initiation and differential growth stages. Yet the underlying molecular pathways integrating the auxin signalling into these two continuous stages of organ formation remain unclear. In a new study, Alon Israeli, Naomi Ori and colleagues uncover an unexpected dual interaction between auxin and gibberellin. To learn more about this work and the people behind it, we talked to first author Alon Israeli and corresponding author Naomi Ori, Professor of Plant Sciences and Genetics in Agriculture at The Robert H. Smith Faculty of Agriculture, Food and Environment, Israel.

While lipid droplets (LDs), organelles central to lipid and energy homeostasis, are implicated in cancer cell migration, their roles during collective cell migration remain unknown. We use Drosophila border cell (BC) migration as an in vivo model of invasive, collective migration to dissect the roles of LDs and the conserved LD lipase, Adipose Triglyceride Lipase (ATGL). LDs undergo dynamic changes and exhibit a polarized distribution during BC migration. Loss of ATGL increases LD volume, whereas BC ATGL overexpression depletes LDs. Loss, knockdown or overexpression of ATGL delays migration and impairs delamination. Additionally, loss of ATGL disrupts BC mitochondria functions, including membrane potential. Similarly, loss of the mitochondrial fatty acid importer, carnitine palmitoyltransferase 1 (CPT1), reduces mitochondrial membrane potential and severely blocks delamination. These results demonstrate that tight regulation of lipid mobilization from LDs, including for energy production, drives delamination and collective migration. These findings not only inform how cancer cells may exploit LDs to promote their invasive behaviors but also highlight the crucial role of LDs in migration during development, hinting at their broader significance in diverse migratory contexts.

The TRIM28 gene encodes a transcriptional regulator involved in a variety of molecular processes. Inactivation of TRIM28 has been linked to the epithelial subtype of Wilms tumor, the most common pediatric renal malignancy. Therefore, TRIM28 may also impact early kidney morphogenesis. To investigate its role in nephrogenesis, we analyzed Trim28 conditional knockout (Trim28Δ/Δ) mice. We found that deleting Trim28 in nephron progenitors resulted in early postnatal lethality and reduced kidney weight. While all renal structures were present, the proximal tubules (PTs) were disorganized. Transcriptome analyses revealed cell-type-specific deregulation of retroelement expression following Trim28 deletion. Further analysis of scRNA-seq data revealed a decreased frequency of nephron progenitor cells (NPCs), an increase in PT cells, and a clear shift towards inflammatory gene expression patterns. While there was no evidence of tumor formation in Trim28Δ/Δ kidneys, the differentially expressed genes in Trim28Δ/Δ progenitors reflected reduced translation, similar to patterns observed in TRIM28 mutant tumor-derived NPCs. Thus, our data demonstrate that TRIM28 primarily influences the maintenance and differentiation of NPCs and PT cells, as well as their subsequent function.

TIE2-ANG1 signalling acts as a master regulator of heart development, playing crucial roles during embryonic cardiac trabeculation. In a new study, Xianghu Qu and colleagues show that endocardial TIE2 signalling in the mammalian embryonic heart promotes endocardial growth by sequestering FOXO1 within the cytoplasm and orchestrates myocardial trabeculation by remodelling the extracellular matrix. To learn more about their work, we talked to the first author Harold Scott Baldwin, as well as the corresponding author, Xianghu Qu, Research Associate Professor of Pediatrics in Cardiology at Vanderbilt University Medical Center, USA.

Teeth serve as a powerful model to dissect epithelial-mesenchymal interaction-mediated organogenesis. While most non-mammalian vertebrates exhibit lifelong tooth renewal (polyphyodonty), mammals have largely lost this capacity and become predominantly diphyodont. Elucidating this evolutionary transition is crucial for understanding developmental constraints on regeneration, yet key mechanisms, particularly how the successional dental lamina persists and how dormant stem cell niches are reactivated, remain largely unresolved. Recent advances in lineage tracing, single-cell sequencing, multi-omics profiling and organoid models have uncovered remarkable cellular diversity and lineage potential during tooth development and homeostasis across vertebrates, reshaping our view of dental stem cell identity and its roles in tissue regeneration. In this Review, we summarize recent progress in tooth development, replacement and molecular regulation, and our current understanding of dental stem cells and organoid models, aiming to delineate a roadmap for translational tooth regeneration.

Anterior-posterior patterning in Drosophila relies on positional information supplied by the graded distributions of three maternally supplied transcription factors originally identified in large-scale mutagenesis screens. Here, I examine the development of embryos in which these three maternal gradients have been flattened, but set at different levels. Following such manipulations, expression patterns at the blastoderm stage are uniform along the anterior-posterior axis, but their specific nature depends on the combination and concentration level of the three systems. Each of the three gradients are then examined in contexts in which the others are flattened but set at different levels. This reveals that each system generates a greater fraction of the wild-type pattern than that deleted when that system is removed by loss-of-function mutations, with the exact pattern depending on the levels to which the two remaining flattened systems are set. These simplified patterns are then used to analyze interactions between the maternal systems and to investigate how the pattern of gap and pair rule genes are modulated by network interactions downstream of the maternal inputs themselves.

The vertebrate limb buds, the embryonic precursors to arms and legs, emerge as cellular outgrowths from the somatic layer of the lateral plate mesoderm. In their work, Vighnesh Ghatpande, Can Cenik and Steve Vokes provide a comprehensive resource defining early regulatory events leading to forelimb bud initiation in the lateral plate mesoderm - a stage that remains poorly understood - and suggests additional roles for TBX5 (the earliest known forelimb-specific marker) beyond Fgf10. To learn more about their work, we talked to the first author Vighnesh Ghatpande, as well as the corresponding authors, Can Cenik, Associate Professor, and Steve Vokes, Professor, both in the Department of Molecular Biosciences, The University of Texas at Austin, USA.

Classical mutagenesis studies in Drosophila identified three graded maternally supplied factors that serve as the initial 'input signal' for anterior-posterior patterning programmes. However, the relative contributions of these factors and how they interact remain unclear. To address this, Eric Wieschaus modulated the gradients of these three factors to disentangle the roles they each play in anterior-posterior patterning. To find out more about this research and how this story developed, we talked to sole author Eric Wieschaus, 1995 Nobel Laureate for Medicine and Emeritus EB and Sons Squibb Professor of Molecular Biology at Princeton University, New Jersey, USA.

Ovarian follicles in most species are assumed to develop using a single pathway. However, in Drosophila pupae, lineage tracing 2,937 single-cell clones identified three follicle "waves" that follow distinct programs arrayed anterior to posterior in the germarium and developing ovarioles. 40 primordial germ cells (PGCs) become anterior germline stem cells (GSCs) that produce "wave 2" follicles throughout adulthood. 100 PGCs posterior to wave 2 develop into "wave 1.5" follicles that form the earliest laid eggs. Different follicle stem cells (FSCs) sequentially occupy the same two niches timed to provide both waves with specific follicle cells, consistent with programmed differences between waves 2 and 1.5. "Wave 1" PGCs located even further posterior proliferate, form cysts, interact with swarm cells, degenerate, break from the ovary 22-26 hours after puparium formation, and release lipid-enriched vacuoles. Some testis germ cells behave similarly. We speculate that wave 1 germ cells contribute directly or indirectly to the pharate adult ecdysone pulse that mediates adult development and sex-specific neural remodeling. Why Drosophila follicle waves generally resemble those clarified recently in mouse preadult ovaries merits additional study.

RNA interference (RNAi) is a genetic tool to disrupt the expression of selected genes by delivering dsRNA into a specific tissue of an organism, resulting in a gene knockdown. We apply RNAi methods to the marine polychaete Streblospio benedicti, which is a model system for studying evolutionary and developmental biology that currently has no established methods for gene expression manipulation. Here we describe a RNAi gene knockdown methodology using two different approaches depending on developmental stage. We fed bacteria expressing dsRNA to early swimming larvae and microinjected in vitro transcribed dsRNA in juveniles. We used two genes for testing: R-opsin and F-actin. For both developmental stages, gene knockdown was assessed using qPCR (quantitative Real-Time PCR). We also visualized RNA expression reduction in larvae using Hybridization Chain Reaction (HCR) in situ hybridization. We show that both delivery methods of larval feeding and juvenile microinjections are sufficient to achieve RNAi gene knockdown, although the specific effect can vary by gene and timing.

The incompleteness of the fossil record and the absence of genetic information limit our ability to understand ancient developmental processes and reconstruct their evolution. Gene expression patterns, physiological pathways, or cellular differentiation processes are rarely preserved, leaving major gaps in our understanding of developmental evolution. Here, we combine comparative and mathematical analyses to uncover an ancestral patterning mechanism underlying the specification of liverwort oil body cells, a synapomorphy of the lineage involved in anti-herbivory defense. We demonstrate that oil body cell homologs in fossils of the oldest known liverwort (Metzgeriothallus sharonae) exhibit spatial organization characteristic of lateral inhibition, including regular spacing and an over-representation of idioblasts. We show that a mechanism involving local activation and lateral inhibition reproduces the diversity of patterns observed in the fossils. Finally, we find that the same mechanism can explain oil body cell patterns in the distantly related liverworts Treubia lacunosa, Apotreubia nana, and Marchantia polymorpha, suggesting a deeply conserved mode of cell specification. Our findings illuminate the origin and diversification of oil body cells, underscoring their evolutionary significance for liverwort development and survival.