Biology subjects

Juliano, C. E.

Publications and source records attributed to Juliano, C. E..

6 recordsLinked to original sources

bioRxiv2025

Sustained ERK signaling couples the injury response to organizer formation during Hydra head regeneration

Regenerative abilities vary widely across animals, even among closely related species, and a central challenge is to compare their gene regulatory networks (GRNs) to determine which components and regulatory connections are conserved or divergent. Hydra provides a powerful system for this work: as a cnidarian, which is the sister group to bilaterians, it offers access to deeply conserved regenerative mechanisms, and species within the genus differ in regenerative phenotypes. Here, we investigate the function of extracellular signal-regulated kinase (ERK) signaling in driving head regeneration in Hydra. ERK is a conserved injury-responsive pathway implicated in regeneration across animals, including in the activation of Wnt signaling, which is necessary and sufficient to establish the Hydra head organizer, a Wnt signaling center that patterns the main body axis. We found that in Hydra vulgaris, ERK activity extends from the generic injury phase into the period when the Wnt-based head organizer forms. However, unlike in some other regenerating species, transient ERK inhibition delayed but did not block regeneration, consistent with Hydras ability to regenerate without a proliferation-dependent blastema. ERK inhibition in H. vulgaris disrupted the transcriptional activation of multiple Wnt pathway components and restricted their expression domains, providing a likely explanation for the delayed onset of head organizer formation. Comparative experiments in Hydra oligactis, which regenerates its head approximately 24 hours more slowly than H. vulgaris, revealed reduced persistence of ERK signaling and lower sensitivity to ERK inhibition. These features suggest that while injury-induced ERK activity is conserved, the mechanisms that establish the Wnt signaling center during regeneration diverge between the two species. Together, our findings identify sustained ERK activity as a critical regulator of Wnt pathway activation during Hydra head regeneration and indicate that evolutionary shifts in the ERK-Wnt regulatory architecture contribute to species-specific differences in regenerative phenotypes.

developmental biology↗

bioRxiv2025

Wnt signaling restores evolutionary loss of regenerative potential in Hydra

The regenerative potential of animals varies widely, even among closely-related species. In a comparative study of regeneration across the Hydra genus, we found that while most species exhibit robust whole-body regeneration, Hydra oligactis and other members of the Oligactis clade consistently fail to regenerate their feet. To investigate the mechanisms underlying this deficiency, we analyzed transcriptional responses during head and foot regeneration in H. oligactis. Our analysis revealed that the general injury response in H. oligactis lacks activation of Wnt signaling, a pathway essential for Hydra vulgaris foot regeneration. Notably, transient treatment with a Wnt agonist in H. oligactis triggered a foot-specific transcriptional program, successfully rescuing foot regeneration. Our transcriptional profiling also revealed dlx2 as a likely high-level regulator of foot regeneration, dependent on Wnt signaling activation. Our study establishes a comparative framework for understanding the molecular basis of regeneration and its evolutionary loss in closely-related species.

developmental biology↗

bioRxiv2021

Single-cell transcriptome reveals insights into the development and function of the zebrafish ovary

Zebrafish are an established research organism that has made many contributions to our understanding of vertebrate tissue and organ development, yet there are still significant gaps in our understanding of the genes that regulate gonad development, sex, and reproduction. Unlike the development of many organs, such as the brain and heart that form during the first few days of development, zebrafish gonads do not begin to form until the larval stage ([≥]5 dpf). Thus, forward genetic screens have identified very few genes required for gonad development. In addition, bulk RNA sequencing studies which identify genes expressed in the gonads do not have the resolution necessary to define minor cell populations that may play significant roles in development and function of these organs. To overcome these limitations, we have used single-cell RNA sequencing to determine the transcriptomes of cells isolated from juvenile zebrafish ovaries. This resulted in the profiles of 10,658 germ cells and 14,431 somatic cells. Our germ cell data represents all developmental stages from germline stem cells to early meiotic oocytes. Our somatic cell data represents all known somatic cell types, including follicle cells, theca cells and interstitial stromal cells. Further analysis revealed an unexpected number of cell subpopulations within these broadly defined cell types. To further define their functional significance, we determined the location of these cell subpopulations within the ovary. Finally, for select examples, we used gene knockout experiments to determine the role of newly identified genes. Our results reveal novel insights into ovarian development and function and the sequencing information will provide a valuable resource for future studies.

developmental biology↗

bioRxiv2020

Oral Regeneration Is the Default Pathway Triggered by Injury in Hydra

In animals capable of whole-body regeneration, a single bisection injury can trigger two different types of regeneration. Currently, it is not well understood how this adaptive response is transcriptionally regulated. We therefore comprehensively characterized transcript abundance and chromatin accessibility during two types of regeneration--oral and aboral regeneration--in the cnidarian Hydra vulgaris. We found that there was an initial generalized response to injury that was not dependent on the type of structure being regenerated. Canonical Wnt signaling, which specifies oral tissue in cnidarians, was activated during this generalized response, likely through the direct upregulation of Wnt ligands by conserved injury-responsive transcription factors. As regeneration progressed, transcription diverged and Wnt signaling became restricted to oral regeneration. We found that TCF, the transcription factor downstream of Wnt signaling, was required for the initiation of oral and aboral-specific transcription, suggesting that the Wnt pathway is important for both types of regeneration. Finally, we found that Wnt signaling was also activated by puncture wounds and that removing pre-existing organizers induced these injuries to undergo ectopic head regeneration. Our work suggests that injuries activate an oral regeneration program, and that other regeneration outcomes are caused by signals from the surrounding tissue. Furthermore, these findings suggest that Wnt signaling may be part of an ancient and conserved metazoan wound response program predating the split of cnidarians and bilaterians.

developmental biology↗

bioRxiv2019

PIWI-piRNA pathway-mediated transposable element repression in Hydra somatic stem cells

Transposable elements (TEs) can damage genomes, thus organisms employ a variety of mechanisms to repress TE expression. However, these mechanisms often fail over time leading to de-repression of TEs in aging tissues. The PIWI-piRNA pathway is a small RNA pathway that represses TE expression in the germline of animals. Here we explore the function of the pathway in the epithelial stem cells of Hydra, a long-lived freshwater cnidarian. Hydra have three stem cell populations; endodermal and ectodermal epithelial stem cells are strictly somatic, whereas the interstitial stem cells retain germline competence. In our previous study, we found that the PIWI proteins are expressed in all three Hydra stem cell types. In this study, we focus on the ectodermal and endodermal epithelial stem cells to understand the somatic function of the pathway. We isolated piRNAs from Hydra that lack the interstitial lineage and found that these somatic piRNAs map predominantly to TE transcripts and display the conserved sequence signatures typical of germline piRNAs. Three lines of evidence suggest that the PIWI-piRNA pathway represses TEs in Hydra epithelial stem cells. First, epithelial knockdown of the Hydra PIWI protein hywi resulted in upregulation of TE expression. Second, degradome sequencing revealed evidence of PIWI-mediated cleavage of TE RNAs in epithelial cells using the ping-pong mechanism. Finally, we demonstrated a direct association between Hywi protein and TE transcripts in epithelial cells using RNA immunoprecipitation. Interestingly, we found that RNAi knockdown of hywi leads to an upregulation of genes involved in innate immunity, which may be in response to TE upregulation; this is consistent with recent studies on TE expression in mammalian cells. Altogether, this study suggests a function for the PIWI-piRNA pathway in maintaining the long-lived somatic cell lineages of Hydra and may point to a broader role for this pathway in protecting somatic tissue from TE-induced damage.

molecular biology↗

bioRxiv2018

Stem cell differentiation trajectories in Hydra resolved at single-cell resolution

The adult Hydra polyp continuously renews all of its cells using three separate stem cell populations, but the genetic pathways enabling homeostatic tissue maintenance are not well understood. We used Drop-seq to sequence transcriptomes of 24,985 single Hydra cells and identified the molecular signatures of a broad spectrum of cell states, from stem cells to terminally differentiated cells. We constructed differentiation trajectories for each cell lineage and identified the transcription factors expressed along these trajectories, thus creating a comprehensive molecular map of all developmental lineages in the adult animal. We unexpectedly found that neuron and gland cell differentiation transits through a common progenitor state, suggesting a shared evolutionary history for these secretory cell types. Finally, we have built the first gene expression map of the Hydra nervous system. By producing a comprehensive molecular description of the adult Hydra polyp, we have generated a resource for addressing fundamental questions regarding the evolution of developmental processes and nervous system function.

developmental biology↗