Biology subjects

Montenegro, J. D.

Publications and source records attributed to Montenegro, J. D..

5 recordsLinked to original sources

bioRxiv2025

Functional analysis of ligand-gated chloride channels in a cnidarian sheds light on the evolution of inhibitory signalling

{psi}-aminobutyric acid (GABA) is the predominant inhibitory transmitter in the vertebrate nervous system. Fast inhibitory signalling is mediated by type A GABA receptors (GABAARs), which form pentameric ligand-gated ion channels. While GABA is also present in plants and prokaryotes, it is unknown when it was first used for fast neuronal transmission. Cnidaria represent a sister group to all Bilateria and possess a variety of putative GABAARs, none of which has been functionally characterized. In this study, we surveyed putative inhibitory ion channel receptors from the model cnidarians Nematostella and Hydra. Phylogenetic analysis revealed a surprising complexity of these receptors. The majority formed a cnidarian-specific radiation with some receptors forming a basal clade. We functionally analyzed seven putative Nematostella GABAARs of this radiation and found that none was activated by GABA or glycine, whereas three were activated by glutamate. Using site-directed mutagenesis, we identified a lysine residue in the canonical ligand-binding pocket that is important for activation by glutamate. Our results identified a group of inhibitory ion channel receptors in Cnidaria that uses glutamate as a ligand. Moreover, they suggest that inhibitory ion channel receptors in Cnidaria massively diversified, which may have been instrumental in the evolution of complex behaviors and sensory processing by the cnidarian nervous system. This work lays the foundation for understanding the diversity and evolution of inhibitory receptors in Cnidaria and the evolution of inhibitory signalling in animal nervous systems.

neuroscience↗

bioRxiv2024

Notch, beta-catenin and MAPK signaling segregate endoderm and mesoderm in the diploblast Nematostella vectensis

Cnidaria are typically considered diploblastic (i.e. consisting of two germ layers) in contrast to their triploblastic sister clade, the Bilateria. However, a recent study suggested that sea anemones and other cnidarians have three segregated germ layer identities, corresponding to the bilaterian germ layers1. Here, we investigated, how the three germ layer identities are specified during early development of the sea anemone Nematostella vectensis. First, the mesodermal territory is specified at the animal pole at 6 hours postfertilization, followed by the specification of a ring of endodermal territory between mesoderm and ectoderm. We then assessed the role of {beta}-catenin, MAPK and Notch signaling pathways during mesoderm and endoderm formation. Our results show that the mesoderm is initiated by MAPK signaling and simultaneously restricted to the future oral side by mutually exclusive nuclear {beta}-catenin signaling. The mesodermal cells then express the Delta ligand, while the ectodermal cells express the Notch receptor. Inhibition of Notch signaling as well as ectopic expression of the Notch intracellular domain showed that endodermal tissue identity is induced by Notch signaling at the boundary between mesoderm and ectoderm. We propose a new model that outlines the different steps leading to the segregation of mesoderm and endoderm identities in Nematostella, confirming the presence of 3 distinct germ layer identities in this cnidarian. Notably, the observed crosstalk of MAPK, {beta}-catenin and Notch signaling in the specification of three germ layers in Nematostella is highly reminiscent to early stage gastrulae of sea urchins suggesting that triploblasty may predate the split of cnidarians and bilaterians.

developmental biology↗

bioRxiv2023

A cell-type atlas from a scyphozoan jellyfish Aurelia coerulea (formerly sp.1) provides insights into changes of cell-type diversity in the transition from polyps to medusae

The life cycle of most medusozoan cnidarians is marked by the metagenesis from the asexually reproducing sessile polyp and the sexually reproducing motile medusa. At present it is unknown to what extent this drastic morphological transformation is accompanied by molecular changes in the cell type composition. Here, we provide a single cell transcriptome atlas of the cosmopolitan scyphozoan Aurelia coerulea focusing on changes in individual cell states during the transition from polyp to medusa. Notably, this transition is marked by an increase in cell type diversity, including an expansion of neural subtypes and the appearance of striated muscles. We find that two families of neuronal lineages are specified by homologous transcription factors in the sea anemone Nematostella vectensis and Aurelia coerulea, suggesting an origin in the common ancestor of medusozoans and anthozoans about 500 Myr ago. Our analysis suggests that gene duplications might be drivers for the increase of cellular complexity during the evolution of cnidarian neuroglandular lineages and highlight the close relationship of neurons and muscles. One key medusozoan-specific cell type is the striated muscle in the subumbrella. Evaluating muscle types by fibre anatomy and gene expression validation of their individual molecular profiles made it possible for the first time to investigate transcriptome differences between smooth and striated muscles. Although smooth and striated muscles are phenotypically different, both have a similar regulation of the contractile complex, reminiscent to the regulation of smooth muscles in bilaterians. This is in contrast to bilaterian striated muscles, where the regulation of muscle contraction involves Ca2+ binding troponins and their interaction with Tropomyosin. This suggests that smooth muscle contraction regulation is ancestral and the use of troponins in striated muscles only evolved in bilaterians. TeaserSingle cell transcriptome atlas across the jellyfish life cycle reveals emergence of novel medusa-specific cell types associated with expression of medusa-specific paralogs.

evolutionary biology↗

bioRxiv2021

Genome assembly of the Australian black tiger shrimp (Penaeus monodon) reveals a fragmented IHHNV EVE sequence

Shrimp are a valuable aquaculture species globally; however, disease remains a major hindrance to shrimp aquaculture sustainability and growth. Mechanisms mediated by endogenous viral elements (EVEs) have been proposed as a means by which shrimp that encounter a new virus start to accommodate rather than succumb to infection over time. However, evidence on the nature of such EVEs and how they mediate viral accommodation is limited. More extensive genomic data on Penaeid shrimp from different geographical locations should assist in exposing the diversity of EVEs. In this context, reported here is a PacBio Sequel-based draft genome assembly of an Australian black tiger shrimp (Penaeus monodon) inbred for one generation. The 1.89 Gbp draft genome is comprised of 31,922 scaffolds (N50: 496,398 bp) covering 85.9% of the projected genome size. The genome repeat content (61.8% with 30% representing simple sequence repeats) is almost the highest identified for any species. The functional annotation identified 35,517 gene models, of which 25,809 were protein-coding and 17,158 were annotated using interproscan. Scaffold scanning for specific EVEs identified an element comprised of a 9,045 bp stretch of repeated, inverted and jumbled genome fragments of Infectious hypodermal and hematopoietic necrosis virus (IHHNV) bounded by a repeated 591/590 bp host sequence. As only near complete linear ~4 kb IHHNV genomes have been found integrated in the genome of P. monodon previously, its discovery has implications regarding the validity of PCR tests designed to specifically detect such linear EVE types. The existence of joined inverted IHHNV genome fragments also provides a means by which hairpin dsRNAs could be expressed and processed by the shrimp RNA interference (RNAi) machinery.

genomics↗

bioRxiv2018

De novo assembly, characterization, functional annotation and expression patterns of the black tiger shrimp (Penaeus monodon) transcriptome

The black tiger shrimp (Penaeus monodon) remains the second most widely cultured shrimp species globally. However, issues with disease and domestication have seen production levels stagnate over the past two decades. To help identify innovative solutions needed to resolve bottlenecks hampering the culture of this species, it is important to generate genetic and genomic resources. Towards this aim, we have produced the most complete publicly available P. monodon transcriptome database to date. The assembly was carried out in multiple assemblers using 2x125 bp HiSeq data from PolyA selected, ribo-depleted RNA extracted from nine adult tissues and eight early life-history stages. In total, approximately 700 million high-quality sequence reads were obtained and assembled into 236,388 clusters. These were then further segregated into 99,203 adult tissue specific clusters, and 58,678 early life-history stage specific clusters. The final transcriptome had a high TransRate score of 0.37, with 88% of all reads successfully mapping back to the transcriptome. BUSCO statistics showed the assembly to be highly complete with low fragmentation, few genes missing, but higher redundancy or transcript duplication (Complete: 98.2% (Duplicated: 51.3%), Fragmented: 0.8%, Missing: 1.0%), and to greatly exceed the completeness of existing P. monodon transcriptomes. While annotation rates were low (approximately 30%), as is typical for a non-model organisms, annotated transcript clusters were successfully mapped to several hundred functional KEGG pathways. To help address the lack of annotation, transcripts were clustered into groups within tissues and early life-history stages, providing initial evidence for their roles in specific tissue functions, or developmental transitions. Additionally, transcripts of shrimp viruses previously not known to occur in Australia were also discovered. We expect the transcriptome to provide an essential resource to investigate the molecular basis of commercially relevant-significant traits in P. monodon and other shrimp species.

molecular biology↗