Eirini Maniou completed her undergraduate degree at the University of Patras, Greece, before moving to the UK to complete a Master\'s at the University of Bath and a PhD at the University of Dundee. For her postdoctoral work at University College London, Eirini turned her attention to neural tube morphogenesis, and she is now employing engineering principles to explore this developmental process at the University of Padua, Italy, where she is a Marie Skłodowska-Curie Actions postdoctoral fellow. Eirini was selected as one of our 2024 PI fellows, a group of researchers who will be supported by Development\'s Pathway to Independence Programme as they aim to secure independent positions. We spoke to Eirini to hear more about her career so far, why she decided to apply to the programme and what research questions she would like to address with her own group.

Keaton Schuster completed his PhD in the lab of Rachel Smith-Bolton at the University of Illinois, USA, investigating Drosophila wing disc regeneration before joining Lionel Christiaen\'s lab at New York University, USA, for his postdoc studying heart regeneration in the chordate tunicate Ciona robusta (formerly Ciona intestinalis type A). Keaton is part of the second cohort of Development\'s Pathway to Independence Programme fellows and we spoke to him over Teams to learn more about his career to date and his future plans for starting his own group continuing to use emerging model systems to study cardiac regeneration.

In a developing nervous system, axonal arbors often undergo complex rearrangements before neural circuits attain their final innervation topology. In the lateral line sensory system of the zebrafish, developing sensory axons reorganize their terminal arborization patterns to establish precise neural microcircuits around the mechanosensory hair cells. However, a quantitative understanding of the changes in the sensory arbor morphology and the regulators behind the microcircuit assembly remain enigmatic. Here, we report that Semaphorin7A (Sema7A) acts as an important mediator of these processes. Utilizing a semi-automated three-dimensional neurite tracing methodology and computational techniques, we have identified and quantitatively analyzed distinct topological features that shape the network in wild-type and Sema7A loss-of-function mutants. In contrast to those of wild-type animals, the sensory axons in Sema7A mutants display aberrant arborizations with disorganized network topology and diminished contacts to hair cells. Moreover, ectopic expression of a secreted form of Sema7A by non-hair cells induces chemotropic guidance of sensory axons. Our findings propose that Sema7A likely functions both as a juxtracrine and as a secreted cue to pattern neural circuitry during sensory organ development.

Lydia Djenoune completed her PhD in the labs of Claire Wyart at the Paris Brain Institute in France and of Hervé Tostivint at the French National Museum of Natural History. She is currently an Instructor in Medicine in Shiaulou Yuan\'s lab at Massachusetts General Hospital (MGH) and Harvard Medical School. Lydia is interested in the role of calcium signalling, cilia and polycystin channels in cardiac development using the zebrafish model. This year, Lydia became one of Development\'s second cohort of Pathway to Independence Programme fellows. We spoke to her over Teams to learn more about her career path so far, the importance of outreach and representation in science, and her plans for her own research group.

Most teleost fishes exhibit a biphasic life history with a larval oceanic phase that is transformed into morphologically and physiologically different demersal, benthic, or pelagic juveniles. This process of transformation is characterized by a myriad of hormone-induced changes, during the often abrupt transition between larval and juvenile phases called metamorphosis. Thyroid hormones (TH) are known to be instrumental in triggering and coordinating this transformation but other hormonal systems such as corticoids, might be also involved as it is the case in amphibians. In order to investigate the potential involvement of these two hormonal pathways in marine fish post-embryonic development, we used the Malabar grouper (Epinephelus malabaricus) as a model system. We assembled a chromosome-scale genome sequence and conducted a transcriptomic analysis of nine larval developmental stages. We studied the expression patterns of genes involved in TH and corticoid pathways, as well as four biological processes known to be regulated by TH in other teleost species: ossification, pigmentation, visual perception, and metabolism. Surprisingly, we observed an activation of many of the same pathways involved in metamorphosis also at an early stage of the larval development, suggesting an additional implication of these pathways in the formation of early larval features. Overall, our data brings new evidence to the controversial interplay between corticoids and thyroid hormones during metamorphosis as well as, surprisingly, during the early larval development. Further experiments will be needed to investigate the precise role of both pathways during these two distinct periods and whether an early activation of both corticoid and TH pathways occurs in other teleost species.

To build a functional inner ear, hair cell morphology must be precisely controlled along the proximo-distal axis. A new paper in Development shows that differential mitochondrial dynamics in proximal versus distal cells impacts on the apical cell surface area - a key aspect of morphology. To find out more about this work, we spoke to first author James O\'Sullivan and senior author Zoë Mann, both at King\'s College London, UK.

Developmental causes of the most common arrhythmia, atrial fibrillation (AF), are poorly defined, with compensation potentially masking arrhythmic risk. Here, we delete 9 amino acids (Δ9) within a conserved domain of the giant protein titin\'s A-band in zebrafish and human-induced pluripotent stem cell-derived atrial cardiomyocytes (hiPSC-aCMs). We find that ttna Δ9/Δ9 zebrafish embryos\' cardiac morphology is perturbed and accompanied by reduced functional output, but ventricular function recovers within days. Despite normal ventricular function, ttna Δ9/Δ9 adults exhibit AF and atrial myopathy, which are recapitulated in TTN Δ9/Δ9-hiPSC-aCMs. Additionally, action potential is shortened and slow delayed rectifier potassium current (I Ks) is increased due to aberrant atrial natriuretic peptide (ANP) levels. Strikingly, suppression of I Ks in both models prevents AF and improves atrial contractility. Thus, a small internal deletion in titin causes developmental abnormalities that increase the risk of AF via ion channel remodeling, with implications for patients who harbor disease-causing variants in sarcomeric proteins.

Girish Kale joined the labs of Thomas Lecuit and Pierre-Francois Lenne at IBDM, Marseille, France for his PhD, where he studied cell mechanics and early development in the fruit fly Drosophila melanogaster. After a 2 year postdoc in Bengaluru, India, he joined Steffen Lemke\'s lab, which recently moved from Heidelberg to the Department of Zoology at the University of Hohenheim, Stuttgart, Germany. His main research interest lies in understanding the effect of temperature on (early) embryonic development. Girish is one of Development\'s Pathway to Independence Programme Fellows, and we caught up with him to find out what drives and excites him, and what he hopes to achieve in his own lab.

OBJECTIVE: Electroanatomical adaptations during the neonatal to adult phase have not been comprehensively studied in preclinical animal models. To explore the impact of age as a biological variable on cardiac electrophysiology, we employed neonatal and adult guinea pigs, which are a recognized animal model for developmental research.
RESULTS: Electrocardiogram recordings were collected in vivo from anaesthetized animals. A Langendorff-perfusion system was employed for the optical assessment of action potentials and calcium transients. Optical data sets were analysed using Kairosight 3.0 software. The allometric relationship between heart weight and body weight diminishes with age, it is strongest at the neonatal stage (R2 = 0.84) and abolished in older adults (R2 = 1E-06). Neonatal hearts exhibit circular activation, while adults show prototypical elliptical shapes. Neonatal conduction velocity (40.6 ± 4.0 cm/s) is slower than adults (younger: 61.6 ± 9.3 cm/s; older: 53.6 ± 9.2 cm/s). Neonatal hearts have a longer action potential duration (APD) and exhibit regional heterogeneity (left apex; APD30: 68.6 ± 5.6 ms, left basal; APD30: 62.8 ± 3.6), which was absent in adults. With dynamic pacing, neonatal hearts exhibit a flatter APD restitution slope (APD70: 0.29 ± 0.04) compared with older adults (0.49 ± 0.04). Similar restitution characteristics are observed with extrasystolic pacing, with a flatter slope in neonates (APD70: 0.54 ± 0.1) compared with adults (younger: 0.85 ± 0.4; older: 0.95 ± 0.7). Neonatal hearts display unidirectional excitation-contraction coupling, while adults exhibit bidirectionality.
CONCLUSIONS: Postnatal development is characterized by transient changes in electroanatomical properties. Age-specific patterns can influence cardiac physiology, pathology, and therapies for cardiovascular diseases. Understanding heart development is crucial to evaluating therapeutic eligibility, safety, and efficacy.

Drosophila border cell clusters model collective cell migration. Airyscan super-resolution microscopy enables fine-scale description of cluster shape and texture. Here we describe how to convert Airyscan images of border cell clusters into 3D models of the surface and detect regions of convex and concave curvature. We use spectral decomposition analysis to compare surface textures across genotypes to determine how genes of interest impact cluster surface geometry. This protocol applies to border cells and could generalize to additional cell types. For complete details on the use and execution of this protocol, please refer to Gabbert et al.1.