Biology subjects

Bajoghli, B.

Publications and source records attributed to Bajoghli, B..

4 recordsLinked to original sources

bioRxiv2026

Temperature scaling of developmental tempo reveals reaction-dominated morphogen patterning

A central question in developmental biology is how embryonic patterning remains robust when developmental tempo changes. In ectotherms, temperature strongly alters developmental speed and biochemical reaction rates, whereas diffusion is expected to change only weakly. How morphogen gradients required for patterning remain correctly scaled under these conditions is unclear. We addressed this problem in medaka embryos by quantifying developmental speed, morphogen clearance, diffusion, and endogenous Nodal dynamics across a broad temperature range. Developmental tempo, morphogen production, clearance, and tissue movement increased approximately two- to threefold per 10{degrees}C, whereas effective morphogen diffusion remained largely unchanged. Despite this mismatch, germ-layer proportions and morphogen patterning remained robust. Our mathematical simulations suggest that this robustness arises because the system operates in a reaction-dominated regime, in which changes in reaction and growth kinetics - rather than diffusion - are sufficient to rescale morphogen gradients. Together, our experiments and simulations provide new insights into how morphogen gradients adjust to maintain accurate tissue patterning across changes in developmental time and tempo.

developmental biology↗

bioRxiv2025

Immune surveillance and pruning of neuronal stem cells in the medaka retina

Stem cell populations in tissues require precise regulation of their number and quality to maintain proper organ growth. Amongst various regulatory mechanisms, immune cells are emerging to directly regulate stem cell populations. The medaka retinal stem cell (RSC) niche, a model for lifelong neurogenic growth, provides a system to study immune-stem cell interactions. We investigate how microglia, resident macrophages of the central nervous system, regulate the RSC niche. We identify that bona fide RSCs express the chemokine Ccl25b while its cognate receptor, Ccr9a, is expressed in microglia. These microglia form a surveillance ring adjacent to the RSC niche and actively phagocytose RSCs. Interference with microglia by deletion of spi1b reveals that microglia absence leads to increased numbers of ccl25b-positive RSCs and results in morphological defects of the retina. Targeted mutation of ccl25b specifically affects microglia mobility under injury conditions, however, we did not observe any morphological defects indicating that Ccl25b-Ccr9a signaling is not essential for stem cell maintenance. Overall, our data show that under homeostatic conditions the individual RSCs, essential for proper eye development, are actively phagocytosed by immune surveillance.

developmental biology↗

bioRxiv2024

Altered thymic niche synergistically drives the massive proliferation of malignant thymocytes

The discovery of genetic alterations in patient samples over the last decades has reinforced a cell-autonomous view of proliferative expansion during T- cell acute lymphoblastic leukemia (T-ALL) development in the thymus. However, the potential contribution of non-cell-autonomous factors, particularly the impact of thymic epithelial cells (TECs) within the thymic niche during the initiation phase, remains unexplored. In this study, we combine a cell-based computational model of the thymus with complementary in vivo experiments in medaka (Oryzias latipes) to systematically analyze the impact of 12 cell-autonomous and non- autonomous factors, individually and in combination, on the proliferation of normal and malignant thymocytes carrying interleukin-7 receptor (IL7R) gain-of-function mutations or elevated IL7R levels, as observed in T-ALL patients. By simulating over 1500 scenarios, we show that while a dense TEC network favored the proliferation of normal thymocytes, it inhibited the proliferation of malignant lineages, which achieved their maximal proliferative capacity when TECs were sparsely distributed. Our in silico model further predicts that specific mutations could accelerate proliferative expansion within a few days. This prediction was experimentally validated, revealing the rapid onset of thymic lymphoma and systemic infiltration of malignant T-cells within just 8 days of embryonic development. These findings demonstrate that synergistic interaction between oncogenic alterations and modifications in the thymic niche can significantly accelerate disease progression. Our results also suggest that negative feedback from the proliferative state suppresses thymocyte differentiation. Overall, this multidisciplinary work reveals the critical role of TEC-thymocyte interactions in both the initiation and progression of T-ALL, highlighting the importance of the thymic microenvironment in early leukemogenesis.

cancer biology↗

bioRxiv2022

Revisiting the origin of interleukin 1 (IL-1) based on biological activities of IL-1 in anamniotes and their sub-functionalization in amniotes

The cytokine Interleukin 1 (IL-1) is an evolutionary innovation of vertebrates. Fish and amphibia have one IL1 gene, while mammals have two copies of IL1, IL1A and IL1B, with distinct expression patterns and differences in their proteolytic activation. Our current understanding of the evolutionary history of IL-1 is mainly based on phylogenetic analyses, but this approach provides no information on potentially different functions of IL-1 homologs, and it remains unclear which biological activities identified for IL-1 and IL-1{beta} in mammals are present in lower vertebrates. Here, we use in vitro and in vivo experimental models to examine the expression patterns and cleavage of IL-1 proteins from various species. We found that IL-1 in the teleost medaka shares the transcriptional patterns of mammalian IL-1, and its processing also resembles that of mammalian IL-1, which is sensitive to cysteine protease inhibitors specific for the calpain and cathepsin families. By contrast, IL-1 proteins in reptiles also include biological properties of IL-1{beta}. Therefore, we propose that duplication of the ancestral IL1 gene led to segregation of expression patterns and protein processing that characterizes the two extant forms of IL-1 in mammals.

immunology↗