Biology subjects

Wessel, G. M.

Publications and source records attributed to Wessel, G. M..

8 recordsLinked to original sources

bioRxiv2026

The tuxedo sea urchin Mespilia globulus: A fast-developing and tractable model for genomic and developmental biology

Sea urchins are pivotal models in cellular and developmental biology, but their biphasic life cycle with an extended larval life limits the ability to study post-metamorphosis and adult characters. Here, we introduce a genomically-enabled model system, the tuxedo urchin Mespilia globulus, which has rapid access to late life stages in sea urchins. We describe how we cultured M. globulus in a landlocked marine facility, raised larvae under artificial conditions and closed their life cycle. We established the experimental tractability of M. globulus: we labelled transcripts by hybridization chain reaction (HCR), and knocked out pigmentation genes to produce albino larvae using CRISPR/Cas9. We generated chromosome-scale genome assemblies for two individuals representing both sexes and two color morphs (red and blue), and compared the organisation of the 21 chromosomes of M. globulus with that of other camarodont echinoid models. We determined that M. globulus showed a conservative gene repertoire lacking the gene family expansions seen in other camarodont sea urchins. We annotated the complement of genes associated with pigmentation, immune and nervous systems and profiled their expressions in tissues and organs. Finally, we surveyed sex-related regions in genomes using genome assemblies and resequencing data, finding no evidence of heteromorphic sex chromosomes in M. globulus. Our findings highlight the accessibility of this new sea urchin model for studying the metamorphosis and adult biology of sea urchins.

evolutionary biology↗

bioRxiv2025

Tomato pollen tube integrity is critical for pollen function at high temperature and is controlled by RALF signaling.

Reproductive success at high temperature (HT) depends on the ability of pollen to germinate a pollen tube that delivers sperm for double fertilization. We recently found that Solanum lycopersicum (tomato) cultivars capable of setting fruit at HT produce pollen tubes that continue to grow under heat stress. Our present goal is to define the molecular basis of thermotolerant pollen tube growth using quantitative live imaging, transcriptomic and proteomic profiling, and genetic analysis. We found that pollen tube integrity - the ability to maintain an intact tip during germination and elongation - was the pollen performance parameter that distinguished thermotolerant cultivars. We identified the components of the Rapid Alkalinization Factor (RALF) pollen tube integrity signal transduction pathway in tomato and found that RALF peptides repress germination at control temperature and that signaling is antagonized by HT. Loss of a single RALF peptide changes pollen tube cell wall pectin distribution and enhances pollen tube integrity at HT in thermotolerant Heinz, revealing that RALF signaling regulates thermotolerant pollen tube growth and establishing a molecular framework for improving reproductive heat-resilience in crop plants.

plant biology↗

bioRxiv2022

Molecular mechanisms of tubulogenesis revealed in the sea star hydro-vascular organ

A fundamental goal in the organogenesis field is to understand how cells organize into tubular shapes. Toward this aim, we have established the hydro-vascular organ in the sea star Patiria miniata as a model for tubulogenesis. In this animal, bilateral tubes grow out from the tip of the developing gut, and precisely extend to specific sites in the larva. This growth requires cell migration coupled with mitosis in distinct zones. Cell proliferation requires FGF signaling, whereas the three-dimensional orientation of the organ depends on Wnt signaling. Specification and maintenance of tube cell fate requires Delta/Notch signaling. Moreover, we identify target genes of the FGF pathway that contribute to tube morphology, revealing molecular mechanisms for tube outgrowth. Finally, we report that FGF activates the Six1/2 transcription factor, which serves as an evolutionarily ancient regulator of branching morphogenesis. This study uncovers novel mechanisms of tubulogenesis in vivo and we propose that cellular dynamics in the sea star hydro-vascular organ represents a key comparison for understanding the evolution of vertebrate organs. Highlights The hydro-vascular organ of the sea star presents a valuable model of tubulogenesis In this organ tube extension is driven by cell migration coupled with cell proliferation at specific growth zones The Wnt pathway controls directional outgrowth The FGF pathway promotes regionalized cell proliferation The Notch/Delta pathway is essential in cell fate repression in tubulogenesis A screen of FGF function revealed essential target gene expression, including the transcription factor Six1/2 Within a sister group to chordates, the sea star will reveal ancient mechanisms of tubulogenesis

developmental biology↗

bioRxiv2022

Elements of divergence in germline determination in closely related species

Evolutionary transitions enable the wide diversity in life histories of plants and animals. This is particularly germane in the development of the germ line in which fitness is a direct readout of evolutionary change. Here, we focused on the gem line of two distinct sea urchin species who shared a common ancestor 50 million years ago. Even though they both rely on inherited mechanisms to specify their germ line, the integration of stage-matched single cell RNA-seq (scRNA-seq) datasets from these two sea urchins revealed a variety of differences in gene expression, including a broader expression of the germ line factor Nanos2 in Lytechinus variegatus (Lv) compared to Strongylocentrotus purpuratus (Sp). In Sp, Nanos2 mRNA expression is highly restricted to the primordial germ cells (PGCs) by a lability element in its 3UTR. This element is lacking in the mRNA of Lv Nanos2, explaining how this mRNA more broadly accumulates in the Lv embryos. We discovered that the Lv Nanos2 3UTR instead leads to a germline specific translation of the protein. The results emphasize that regulatory mechanisms resulting in germline diversity rely less on transcriptional regulation and more on post-transcriptional and post-translational restrictions of key gene products, such as Nanos2. Highlights- The first integration of scRNA-seq datasets comparing two echinoderm species. - We find Nanos2 positive cells in the embryonic soma of Lytechinus variegatus, an unusual occurrence, but not in Strongylocentrous purpuratus. - We discovered that this somatic Nanos2 mRNA is lacking an important regulatory element (GNARLE) in its 3UTR - Instead, in Lv, the 3UTR of Nanos2 leads to its specific translation in the germ cells.

developmental biology↗

bioRxiv2022

Distinct mechanisms of germ cell factor regulation for an inductive germ cell fate

Specification of primordial germ cells (PGCs), the lineage which gives rise to eggs and sperm, is essential for sexually reproducing organisms. The mechanism by which animals specify their PGCs generally falls into two categories: inherited or inductive. The inductive mechanism, used by mammals, relies on cell signaling interactions to direct a subset of embryonic cells to a germ cell fate. Previous work suggested that sea star embryos, which develop in simple culture and are markedly transparent, also use inductive mechanisms to specify their germline. The germ cell factors Nanos and Vasa become restricted during early development into a localized region of cells within the posterior enterocoel (PE), the presumptive germline. Nodal signaling was observed to negatively regulate Vasa and Nanos mRNAs outside of the PE and restrict the germline to the PE. Here we employed single cell RNA sequencing to identify the transcriptional program of germ cells and their changes during development. We never see Nodal pathway members within Nanos/Vasa positive cells in the region known to give rise to the PE, and instead see members of the Wnt-signaling pathway and the FoxY family of transcription factors. We learned that Wnt and Delta/Notch signaling enhances expression of both Nanos and Vasa, whereas a test of cell interactions reveals that Nanos and Vasa are regulated distinctly. This work provides insights into the sequence of events that leads to PGC specification and enables deeper mechanistic studies in a tractable in vivo model. HighlightsO_LISingle-cell RNA-sequencing of sea star embryos demonstrates temporal differences in cell fate commitment among echinoderms. C_LIO_LISea urchin and sea star embryos appear to ascribe their germ line by two extreme different mechanisms but share similar pathways in regulation of the germline genes. C_LIO_LIExpression of the germline factors, Vasa and Nanos, is regulated by distinct mechanisms in the sea star. C_LIO_LIGermline induction in the sea star uses similar signaling mechanisms as mammals. C_LI

developmental biology↗

bioRxiv2022

Sex-Specific Genes Identified in Sea Urchin Gonads are Expressed Prior to Metamorphosis

A great collaboration between the germline and somatic cells of an organism is the creation of a functional gonad. Here we begin to test this mechanism in a sea urchin by use of RNA-seq, and quantitative mRNA measurements throughout the life cycle of the sea urchin, Lytechinus variegatus (Lv). We found through de novo analyses that the ovary and testis of this echinoderm contains the many transcripts predicted for gamete morphology and function, but we also discovered many uncharacterized gene products unique to each gonad. We found that transcripts involved in glycolysis are highly enriched in the ovary compared to the testis, and that Lv has an expansion of nanos genes not observed in other sequenced echinoderms. We developed a pipeline integrating timepoint RNA-seq data throughout development to identify hallmark gene expression in gonads. We found activation of meiotic genes surprisingly early in development, and observed that candidate genes involved in sex determination are first expressed during larval growth, well before metamorphosis. We further discovered that individual larvae express varying levels of male- or female-hallmark genes before metamorphosis, including factors for the germ line, oocyte, sperm, and meiosis related genes. Together these data support the hypothesis that sex determination in the sea urchin is initiated prior to metamorphosis, from a shared profile of male and female factors, and that the many uncharacterized genes unique to the gonads may reveal unique pathways and mechanisms in echinoderm reproduction. HighlightO_LITestis and Ovary of the sea urchin, Lytechinus variegatus, have distinct transcriptome profiles C_LIO_LIL. variegatus gonad RNA-seq reveals the expression of 9 nanos genes C_LIO_LIThe ovary in the sea urchin uniquely expresses genes of the glycolytic pathway, including an ovary-specific transcript of GAPDH C_LIO_LIGenes involved in meiosis and in sex determination are expressed early in larval development C_LIO_LIFrom gene expression profiles we conclude here that sex determination is initiated prior to metamorphosis in this echinoderm C_LI

developmental biology↗

bioRxiv2021

Polarized Dishevelled dissolution and condensation drives embryonic axis specification in oocytes

The organismal body axes that are formed during embryogenesis are intimately linked to intrinsic asymmetries established at the cellular scale in oocytes [1]. Here, we report an axis-defining event in meiotic oocytes of the sea star Patiria miniata. Dishevelled is a cytoplasmic Wnt pathway effector required for axis development in diverse species [2-4], but the mechanisms governing its function and distribution remain poorly defined. Using time-lapse imaging, we find that Dishevelled localizes uniformly to puncta throughout the cell cortex in Prophase I-arrested oocytes, but becomes enriched at the vegetal pole following meiotic resumption through a dissolution-condensation mechanism. This process is driven by an initial disassembly phase of Dvl puncta, followed by selective reformation of Dvl assemblies at the vegetal pole. Rather than being driven by Wnt signaling, this localization behavior is coupled to meiotic cell cycle progression and influenced by Lamp1+ endosome association and Frizzled receptors pre-localized within the oocyte cortex. Our results reveal a cell cycle-linked mechanism by which maternal cellular polarity is transduced to the embryo through spatially-regulated Dishevelled dynamics.

cell biology↗

bioRxiv2019

Optimization of the cultivation conditions of indigenous wild yeasts and evaluation of their leavening capacity: Isolated from fermented foods and beverages.

Ethiopia has a high demand for bakers yeast in the bread and beverage industries. Unfortunately, Ethiopia has no producing plant for bakers yeast and instead relies on costly imports. The objective of this work was to identify the most productive and useful indigenous bakers yeasts isolated from local fermented foods and drinks, honey and Molasses using leavening ability as the major metric. Six of the test isolates produced a maximum cell mass at 30{degrees}C, pH of 5.5 and 48 hours of incubation. Isolate AAUTf1 did not produce hydrogen sulfide, while isolates AAUTf5, AAUTj15 and AAUSh17 produced low levels of this chemical, and isolates AAUMl20 and AAUWt21 produced high levels of hydrogen sulfide, neglecting their utility in baking. The leavening performance of isolates AAUTf1 (Candida humilis) and AAUTf5 (Kazachstania bulderi) had the highest dough volume of 131 cm3 and 128 cm3 respectively in 120 min. Isolates AAUSh17 (Saccharomyces cerevisiae) and AAUTj15 (Saccharomyces cerevisiae) raised the dough volume of 127 cm3 and 125 cm3 respectively, at 60 min compared to commercial yeast (117 cm3 in 90 min). The study also revealed that mixed cultures of indigenous yeasts had better leavening capacity than single cultures. The co-inoculated cultures of AAUTf1 + AAUTf5 + AAUTj15, AAUTf5 + AAUTj15, and AAUTf1 + AAUTj15 + AAUSh17 reached 143 cm3 at 90 min, 141 cm3 and 140 cm3 both at 60 min, respectively. Thus, the indigenous isolates are candidates for optimizing utilization of yeast for fast promotion and utilization in the bakery industries.

microbiology↗