Biology subjects

Haas, F.

Publications and source records attributed to Haas, F..

5 recordsLinked to original sources

bioRxiv2026

Life-cycle plasticity enables conditional asexual reproduction in a kelp

Many organisms alternate between distinct life stages and can reproduce either sexually or asexually, yet the mechanisms coordinating these developmental and reproductive transitions remain poorly understood. Here, we investigate the molecular basis of life stage identity and reproductive mode in the kelp Laminaria pallida, a multicellular organism with a complex life cycle. By combining gene expression analyses with developmental experiments and natural population-level approaches, we identify the genetic networks that govern developmental state transitions in both sexual and asexual contexts. We show that the capacity for asexual reproduction is broadly retained but rarely expressed in natural populations and is associated with reduced fitness. Moreover, we find that the presence of potential mating partners suppresses asexual development, revealing that reproductive mode is actively adjusted in response to reproductive opportunities. Together, these findings suggest that asexual reproduction functions as a conditional alternative to sex, promoting persistence when sexual reproduction is constrained while preserving the long-term benefits of sexual reproduction when mates are available. More broadly, our results reveal how organisms integrate developmental, environmental, and reproductive cues to balance alternative reproductive strategies across complex life cycles.

Developmental Biology↗

bioRxiv2025

Notch coordinates self-organization of germ layers and axial polarity in cnidarian gastruloids

Dissociation and reaggregation experiments in several animal systems have revealed the stunning capacity of self-organization. Reaggregated early gastrula cells (here called gastruloids) of the sea anemone Nematostella vectensis are able to regenerate with only little delay whole organisms that are virtually indistinguishable from normal developing polyps. However, the molecular control underlying the restoration of body axis and germ layers remains largely unknown. To address this, we established a standardized protocol, which reproducibly generates gastruloids developing into polys with a single body axis. Here, we show that committed mesodermal and endodermal cells are sorted out to the surface of the aggregate, where mesodermal cells form clusters of about 30 cells. At a critical time point, one mesodermal cluster immigrates, along with peripherally attached endodermal cells. Thereby, the inner germ layer and the oral-aboral axis is established in one and the same process. Functional studies demonstrated that this polarization of the endodermal cells requires a feedback loop of Notch and Wnt signaling. The dissociation of the early embryo disrupts Notch signaling in the endodermal cells, which leads to transient adoption of an endomesodermal profile, marked by the expression of the mesodermal cadherin1 until the boundaries between the germ layer identities are re-established. Our results highlight distinct morphogenetic behaviors of mesodermal and endodermal cells and the hitherto unknown role of Notch signaling in germ layer boundary formation in self-organizing gastruloids. Conservation of Notch-mediated boundary formation between endoderm and mesoderm mirrors bilaterian mechanisms, demonstrating how adoption of ancestral regulatory networks governing morphogenesis likely enabled the diversification of metazoan body plans.

developmental biology↗

bioRxiv2023

Nanos2+ cells give rise to germline and somatic lineages in the sea anemone Nematostella vectensis

In all animals, stem cell populations of varying potency facilitate regeneration and tissue homeostasis. Notably, germline stem cells in both vertebrates and invertebrates express highly conserved RNA-binding proteins, such as nanos, vasa and piwi. Interestingly, in animals, which are capable of whole-body regeneration, such as poriferans, hydrozoans and planarians, these genes are also expressed in somatic multi- and pluripotent stem cells, which led to the proposal that they had an ancestral role in all stem cells. While multi- and pluripotent interstitial stem cells have been identified in hydrozoans, they have not unambiguously been demonstrated in other cnidarian classes. Therefore, it is currently unclear if these stem cell systems share a common evolutionary origin or have been adapted individually in different lineages as homoplasy. We therefore aimed to characterize stem cells expressing conserved stem cell marker genes in the sea anemone Nematostella vectensis, to gain insight of shared traits governing the regulation of this enigmatic cell type. Through single cell transcriptomics, we identify cell populations expressing the germline associated markers piwi1 and nanos2 in the soma and germline. Transgenic reporter genes reveal a lineage giving rise to somatic cells, consistent with a role as a multipotent stem cell population. Cell proliferation studies show that a fraction of nanos2+ reporter cells are cycling and CRISPR/Cas9 mediated gene knockout show that nanos2+ progenitor cells are indispensable for male and female germline maintenance in Nematostella. This suggests nanos and piwi genes have a conserved role in somatic and germline stem cells in cnidarians.

developmental biology↗

bioRxiv2023

Impact of inflammatory preconditioning on murine microglial proteome response induced by focal ischemic brain injury

Preconditioning with LPS induces neuroprotection against subsequent cerebral ischemic injury, mainly involving innate immune pathways. Microglia are CNS-resident immune cells that respond early to danger signals through memory-like differential reprogramming. However, the cell-specific molecular mechanisms underlying preconditioning are not fully understood. To elucidate the distinct molecular mechanisms of preconditioning on microglia, we compared these cell-specific proteomic profiles in response to LPS preconditioning and without preconditioning and subsequent transient focal brain ischemia and reperfusion, - using an established mouse model of transient focal brain ischemia and reperfusion. A proteomic workflow, based on isolated microglia obtained from mouse brains by cell sorting and coupled to mass spectrometry for identification and quantification, was applied. Our data confirm that LPS preconditioning induces marked neuroprotection, as indicated by a significant reduction in brain infarct volume. The established brain cell separation method was suitable for obtaining an enriched microglial cell fraction for valid proteomic analysis. The results show a significant impact of LPS preconditioning on microglial proteome patterns by type I interferons, presumably driven by the interferon cluster regulator proteins Stat1/2.

neuroscience↗

bioRxiv2019

Genome improvement and genetic map construction for Aethionema arabicum, the first divergent branch in the Brassicaceae family

BackgroundThe genus Aethionema is a sister-group to the core-group of the Brassicaceae family that includes Arabidopsis thaliana and the Brassica crops. Thus, Aethionema is phylogenetically well-placed for the investigation and understanding of genome and trait evolution across the family. We aimed to improve the quality of the reference genome draft version of the annual species Aethionema arabicum. Secondly, we constructed the first Ae. arabicum genetic map. The improved reference genome and genetic map enabled the development of each other.\n\nResultsWe started with the initially published genome (version 2.5). PacBio and MinION sequencing together with genetic map v2.5 were incorporated to produce the new reference genome v3.0. The improved genome contains 203 MB of sequence, with approximately 94% of the assembly made up of called bases, assembled into 2,883 scaffolds. The N50 (10.3 MB) represents an 80-fold over the initial genome release. We generated a Recombinant Inbred Line (RIL) population that was derived from two ecotypes: Cyprus and Turkey (the reference genotype. Using a Genotyping by Sequencing (GBS) approach, we generated a high-density genetic map with 749 (v2.5) and then 632 SNPs (v3.0) was generated. The genetic map and reference genome were integrated, thus greatly improving the scaffolding of the reference genome into 11 linkage groups.\n\nConclusionsWe show that long-read sequencing data and genetics are complementary, resulting in an improved genome assembly in Ae. arabicum. They will facilitate comparative genetic mapping work for the Brassicaceae family and are also valuable resources to investigate wide range of life history traits in Aethionema.

genomics↗