Distinct vitellogenin domains differentially regulate immunological outcomes in invertebrates

Bioinformatics analyses of the proteome of Holothuria tubulosa coelomic fluid and the first evidence of primary cilium in coelomocyte cells

The holothurian immune system is characterized by complex defense mechanisms that act through humoral and cellular pathways. Coelomocites are the cellular component of coelomic fluid, and they are involved in host defense, stress response, wound healing, organ regeneration, and tissue homeostasis. The close phylogenetic relationship between Holothuria tubulosa and chordate phylum makes it a good model for studying the evolution of immune processes. To elucidate the immune landscape in H. tubulosa, we applied an approach combining proteomic analysis of coelomic fluid separated into cellular fraction and extracellular fraction and bioinformatics and in silico analyses. A Search Tool for the Retrieval of Interacting Genes/Protein analysis indicated a highly functional homology to the human protein of immune recognition factors, non-canonical immune-related proteins, signaling molecules, and effector protein, cytoskeleton, and actin remodeling, and provided the first evidence in invertebrate immune cells of an intracellular protein fraction linked to ancestral structure resembling primary cilium involved in cell signaling.

Phosphorylated Eriocheir sinensis Rab10 regulates apoptosis and phagocytosis to defense Spiroplasma eriocheiris infection

The Rab GTPases play a crucial role in the regulation of immune responses towards viruses and bacteria infection in invertebrates. The proteomic data revealed Eriocheir sinensis Rab10 (EsRab10) phosphorylation was strongly decreased following Spiroplasma eriocheiris infection. However, the regulatory mechanism by which Rab10 modulates the innate immunity of E. sinensis against S. eriocheiris infection remains to be elucidated. In the present study, the coding sequence of EsRab10 identified as 609 bp, encoding a protein of 203 amino acids. EsRab10 was highly transcribed in diverse immune-related tissues of crab, including hepatopancreas, gills, and hemocytes, with a notable downregulation observed after S. eriocheiris infection. Knockdown of EsRab10 via RNA interference (RNAi) led to a significant increase in hemocyte apoptosis and a marked reduction in the phagocytic capacity of hemocytes against S. eriocheiris. Furthermore, EsRab10 RNAi resulted in an elevated S. eriocheiris load in hemocytes and a significant decrease in crab survival rates. Overexpression of EsRab10 in Drosophila Schneider 2 (S2) cells demonstrated that phosphorylation of EsRab10 enhanced cell viability, reduced apoptosis, increased phagocytic activity, and decreased the S. eriocheiris load in S2 cells. Conversely, dephosphorylation of EsRab10 exerted opposite effects. In summary, these results demonstrated that EsRab10 played a crucial role in the resistance of E. sinensis to S. eriocheiris infection by modulating apoptosis and phagocytosis through phosphorylation.

Midgut-specific vitellogenin-1 is involved in the negative regulation of Babesia ovata migration or proliferation in Haemaphysalis longicornis tissues

Transovarial transmission of bovine Babesia has been experimentally demonstrated using larvae from Haemaphysalis longicornis ticks that are parasitized on cattle infected with Babesia ovata. However, the molecular mechanisms underlying this transovarial transmission remain unclear. We previously showed that vitellogenin (Vg) and its receptor, essential for oogenesis, are key factors involved in Babesia infection in the ovary of H. longicornis. So far, three Vg genes (HlVg-1, HlVg-2, and HlVg-3) have been identified from H. longicornis, but the roles of Vgs other than HlVg-2 in Babesia-infected ticks are unknown. Here, we report the estimated roles of midgut-specific HlVg-1 in Babesia-infected ticks. Following semi-artificial feeding of B. ovata-infected bovine red blood cells, the expression level of HlVg-1 was significantly upregulated at 1 and 2 days after engorgement (dAE). Subsequently, gene silencing mediated via RNA interference (RNAi) was performed to infer the role of HlVg-1 in B. ovata-infected ticks. Interestingly, relative detection levels of Babesia DNA in HlVg-1 RNAi ticks were higher compared with control ticks at 1 and 2 dAE. These results indicate that HlVg-1 might regulate tissue-to-tissue migration or proliferation of Babesia in the tick body. Our data hypothesize that each organ-specific Vg has individual roles during Babesia infection.

How Insects Balance Reproductive Output and Immune Investment

Insects face the constant challenge of balancing energy allocation between reproduction and immune responses, both of which are highly energy-demanding processes. Immune challenges frequently result in decreased fecundity, reduced egg viability, and delayed ovarian development. Conversely, heightened reproductive activity often suppresses immune functions. This trade-off has profound ecological and evolutionary consequences, shaping insects' survival, adaptation, and population dynamics. The intricate interplay between reproduction and immunity in insects is regulated by the neuroendocrine and endocrine systems, which orchestrate resource distribution alongside other biological processes. Key hormones, such as juvenile hormone and ecdysteroids, serve as central regulators, influencing both immune responses and reproductive activities. Additionally, macromolecules like vitellogenin and lipophorin, primarily known for their functions as yolk protein precursors and lipid carriers, play crucial roles in pathogen recognition and transgenerational immune priming. Advancements in molecular and omics tools have unveiled the complexity of these regulatory mechanisms, providing new insights into how insects dynamically allocate resources to optimize their fitness. This delicate balance underscores critical evolutionary strategies and the integration of physiological systems across species. This review synthesizes insights from life history theory, oogenesis, and immunity, offering new perspectives on the trade-offs between reproductive output and immune investment.

Feeding on different hosts displays different hemolymph protein compositions in Haemaphysalis qinghaiensis tick

Tick hemolymph plays an important role in the transportation of nutrients as well as metabolites. The hemolymph consists of plasma and blood cells, and proteins are the main components of plasma. This study aimed to investigate the protein composition of the hemolymph of Haemaphysalis qinghaiensis and to explore the effects of different hosts on the hemolymph protein composition of ticks, which could provide a reference for the screening of tick-protective antigens. Hemolymph was collected from the engorged females of the H. qinghaiensis ticks from the Bos grunniens (HqB) and Ovis aries (HqO) hosts. We identified 17 host-derived high-confidence proteins and 156 tick-derived high-confidence proteins from HqB. Fifteen host-derived high-confidence proteins and 155 tick-derived high-confidence proteins were identified from HqO. There were significant differences in the composition and abundance of the host-derived protein in the hemolymph from the two sources, with fibrinogen, alpha-1-antiproteinase, α-2-macroglobulin, and an uncharacterized protein present only in HqB, while ubiquitin-60S ribosomal protein L 40 was found only at HqO. Besides, the abundance of these proteins also varied significantly. The 163 tick-derived proteins identified are classified as enzymes, inhibitors, transporters, immunity-related proteins, cytoskeletal proteins, heat shock proteins, nuclear proteins, other proteins, uncharacterized proteins, and secreted proteins. The KGD sequence of A1 in the uncharacterized protein suggested that the unidentified protein may be associated with anti-coagulants, but further research was needed to confirm the function of these uncovered proteins. HqB and HqO shared a total of 148 tick-derived proteins, with eight proteins present only in HqB and seven only in HqO. The abundance of 65 shared proteins was significantly higher in HqO. In conclusion, the hemolymph proteins of H. qinghaiensis tick were composed of host-derived and tick-derived proteins. Different blood meals had a large effect on the composition and abundance of both host-derived and tick-derived proteins.

Identification of a Mnlrig-1 involved in testis reproductive immunity in the oriental river prawn Macrobrachium nipponense

The testis evolves a highly organized testicular microenvironment to support spermatogenesis. However, the knowledge about it is limited in crustacean. In this study, we identified a member of immunoglobulin superfamily (IgSF) from Macrobrachium nipponense testis and explored its roles as a potential pattern recognition receptor (PRR) involved in reproductive immunity. Based on the domains it contains and homology analysis result, we designate it as leucine-rich repeats and immunoglobulin-like domains protein-1 (MnLrig-1). The Mnlrig-1 comprises a 3288 bp open reading frame (ORF) encoding a 1095 amino acid protein. MnLrig-1 is consisted of one signaling peptide; one LRR_NT domain; eight LRR domains; five LRR_TYP domains; one LRR_CT domain; three IGc2 regions; one transmembrane region, and C-terminal cytoplasmic tail, sharing similar domains with orthologs in other crustacean species. MnLrig-1 is widely expressed in various tissues of M. nipponense. Mnlrig-1 is significantly induced by LPS, PGN, Aeromonas hydrophila, and Vibrio alginolyticus challenge in the testis at 3 h and maintained a high level from 3 h to 24 h. Additionally, two recombinant immunoglobulin domains of MnLrig-1 are obtained, while only one domain shows direct binding affinity towards LPS, PGN, Escherichia coli, A. hydrophila, Staphylococcus aureus, and Bacillus subtilis in vitro. Moreover, silencing Mnlrig-1 results in a significant upregulation of three anti-lipopolysaccharide factors (ALFs) in the testis. These results reveal the potential role of MnLrig-1 as a PRR involved in the testis reproductive immunity in M. nipponense. The insights gained from this study will expand our understanding of immune system in crustacean and may have implications for aquaculture and disease management in crustaceans.

Comparative transcriptome analysis reveals the different responding mechanisms of ovary and hepatopancreas following polyI:C challenge in Macrobrachium nipponense

The ovary in mammals has developed specialized mechanisms for protection against pathogen infections; however, the understanding of the innate immune system in the ovary of crustaceans is still limited. To elucidate the ovary's defense mechanisms in response to viral challenges, we subjected oriental river prawns (Macrobrachium nipponense) to poly I:C, a double-stranded RNA analog that emulates viral dsRNA, and analyzed the ovary's transcriptome profiles. Concurrently, RNA-seq analysis was performed on the hepatopancreas, a well-recognized immune-related tissue, following poly I:C challenge to investigate the distinct response mechanisms of the ovary and hepatopancreas and to gain a comprehensive understanding of the immune responses in both tissues. The results indicate that 1368 genes are differentially expressed in the ovary, with 903 genes upregulated and 465 genes downregulated. Subsequent analysis reveals that these differentially expressed genes (DEGs) include numerous genes associated with innate immunity, such as members of the C-type lectin, fibrinogen-related protein (Frep), Toll-like receptor, and NOD-like receptor (NLR) gene families, as well as acid phosphatase, scavenger receptor, crustin, Down syndrome cell adhesion molecule (Dscam), hemocyanin, and lipopolysaccharide and beta-1,3-glucan binding protein (LGBP). Furthermore, the DEGs include several genes related to ovary development, such as sox8, vitellogenin, progranulin, cyclin-dependent kinase, ecdysone receptor, frizzled, and members of the Fox gene family. In the hepatopancreas, a total of 729 DEGs were identified. Comparison of the DEGs in both tissues indicates that only 91 genes are common to both groups, highlighting significant tissue-specific responses to poly I:C stimulation. This study aims to enhance our understanding of the immune protective mechanisms employed by the ovary in response to pathogen exposure and establishes a foundation for investigating ovarian reproductive immunity in crustaceans.

A pattern recognition receptor interleukin-1 receptor is involved in reproductive immunity in Macrobrachium nipponense ovary

The family of TIR domain-containing receptors includes numerous proteins involved in innate immunity. In this study, a member of this family was characterized from the ovary of the oriental river prawn Macrobrachium nipponense and identified as interleukin-1 receptor (MnIL-1R). Meanwhile, to elucidate the conservation of IL-1R, its orthologous were identified in several crustacean species as well. In addition, the expression pattern of MnIL-1R in various adult tissues and post different pathogen-associated molecular patterns (PAMPs) challenge in ovary was analyzed with qRT-PCR technology. Finally, the roles of MnIL-1R in the ovary were analyzed by RNAi technology. The main results are as follows: (1) MnIL-1R comprises a 1785 bp ORF encoding 594 amino acids and is structurally composed of five domains: a signal peptide, two immunoglobulin (IG) domains, a transmembrane region, and a TIR-2 domain; (2) the TIR domain showed a high conservation among analyzed crustacean species; (3) MnIL-1R is widely detected in all tested tissues including ovary; (4) MnIL-1R showed a positive response to challenges with LPS, PGN, and polyI:C in the ovary; (5) its IG domain showed strong binding ability to LPS and PGN, confirming its role as a pattern recognition receptor; (6) the expression patterns of several members of the Toll signaling pathway (Myd88, TRAF-6, Dorsal, and Relish) was similar to that of MnIL-1R after challenges with LPS, PGN, and polyI:C in the ovary; (7) the silencing of MnIL-1R resulted in down-regulation of theses gene' (Myd88, TRAF-6, Dorsal, and Relish) expression level in the ovary. These results suggest that MnIL-1R can activate the Toll signaling pathway in the ovary by directly recognizing LPS and PGN through its IG domain, thereby contributing to the immune response in the ovary of M. nipponense.

Vitellogenin and its upstream gene TOR play essential roles in the reproduction of Dermanyssus gallinae

In Dermanyssus gallinae, a hematophagous mite, the initiation of vitellogenesis induced by blood feeding is essential for its reproduction. However, the precise gene structures and physiological functions of Vg in D. gallinae and its upstream gene, Target of Rapamycin (TOR), have not been fully understood. This study revealed the presence of four homologous genes within D. gallinae, named Dg-Vg1, Dg-Vg1-like, Dg-Vg2, and Dg-Vg2-like, especially, Dg-Vg2-like was firstly identified in the mites. The expression levels of all these Vg genes were significantly higher in adult females than other stages. Following blood feeding, the expression levels of these genes increased significantly, followed by a subsequent decrease, aligning with egg production. Silencing Dg-Vgs by RNA interference (RNAi) led to decreased fecundity and egg hatching rates, as well as abnormal embryonic development, suggesting a vital role for Dg-Vgs in both egg formation and embryonic development. Furthermore, the knockdown of Dg-TOR significantly reduced the expression of Dg-Vgs and negatively impacted the reproductive capabilities of PRMs, indicating that TOR influences PRM reproduction by regulating the expression of Dg-Vgs. In summary, these findings demonstrated the crucial roles of Dg-Vgs and Dg-TOR in PRM reproduction, highlighting their potential as targets for pest control.

Sex-Biased Transcription Expression of Vitellogenins Reveals Fusion Gene and MicroRNA Regulation in the Sea Louse Caligus rogercresseyi

The caligid ectoparasite, Caligus rogercresseyi, is one of the main concerns in the Chilean salmon industry. The molecular mechanisms displayed by the parasite during the reproductive process represent an opportunity for developing novel control strategies. Vitellogenin is a multifunctional protein recognized as a critical player in several crustaceans' biological processes, including reproduction, embryonic development, and immune response. This study aimed to characterize the C. rogercresseyi vitellogenins, including discovering novel transcripts and regulatory mechanisms associated with microRNAs. Herein, vitellogenin genes were identified by homology analysis using the reference sea louse genome, transcriptome database, and arthropods vitellogenin-protein database. The validation of expression transcripts was conducted by RNA nanopore sequencing technology. Moreover, fusion gene profiling, miRNA target analysis, and functional validation were performed using luciferase assay. Six putative vitellogenin genes were identified in the C. rogercresseyi genome with high homology with other copepods vitellogenins. Furthermore, miR-996 showed a putative role in regulating the Cr_Vitellogenin1 gene, which is highly expressed in females. Moreover, vitellogenin-fusion genes were identified in adult stages and highly regulated in males, demonstrating sex-related expression patterns. In females, the identified fusion genes merged with several non-vitellogenin genes involved in biological processes of ribosome assembly, BMP signaling pathway, and biosynthetic processes. This study reports the genome array of vitellogenins in C. rogercresseyi for the first time, revealing the putative role of fusion genes and miRNA regulation in sea lice biology.

Genome-Wide Identification of Vitellogenin Gene Family and Comparative Analysis of Their Involvement in Ovarian Maturation in Exopalaemon carinicauda

Vitellogenin (Vtg) is a precursor of yolk proteins in egg-laying vertebrates and invertebrates and plays an important role in vitellogenesis and embryonic development. However, the Vtg family remains poorly characterized in Exopalaemon carinicauda, a major commercial mariculture species found along the coasts of the Yellow and Bohai Seas. In this study, 10 Vtg genes from the genomes of E. carinicauda were identified and characterized. Phylogenetic analyses showed that the Vtg genes in crustaceans could be classified into four groups: Astacidea, Brachyra, Penaeidae, and Palaemonidae. EcVtg genes were unevenly distributed on the chromosomes of E. carinicauda, and a molecular evolutionary analysis showed that the EcVtg genes were primarily constrained by purifying selection during evolution. All putative EcVtg proteins were characterized by the presence of three conserved functional domains: a lipoprotein N-terminal domain (LPD_N), a domain of unknown function (DUF1943), and a von Willebrand factor type D domain (vWD). All EcVtg genes exhibited higher expression in the female hepatopancreas than in other tissues, and EcVtg gene expression during ovarian development suggested that the hepatopancreas is the main synthesis site in E. carinicauda. EcVtg1a, EcVtg2, and EcVtg3 play major roles in exogenous vitellogenesis, and EcVtg3 also plays a major role in endogenous vitellogenesis. Bilateral ablation of the eyestalk significantly upregulates EcVtg mRNA expression in the female hepatopancreas, indicating that the X-organ/sinus gland complex plays an important role in ovarian development, mostly by inducing Vtg synthesis. These results could improve our understanding of the function of multiple Vtg genes in crustaceans and aid future studies on the function of EcVtg genes during ovarian development in E. carinicauda.

Microsporidian Nosema bombycis hijacks host vitellogenin and restructures ovariole cells for transovarial transmission

Microsporidia are a group of obligate intracellular parasites that infect almost all animals, causing serious human diseases and major economic losses to the farming industry. Nosema bombycis is a typical microsporidium that infects multiple lepidopteran insects via fecal-oral and transovarial transmission (TOT); however, the underlying TOT processes and mechanisms remain unknown. Here, we characterized the TOT process and identified key factors enabling N. bombycis to invade the ovariole and oocyte of silkworm Bombyx mori. We found that the parasites commenced with TOT at the early pupal stage when ovarioles penetrated the ovary wall and were exposed to the hemolymph. Subsequently, the parasites in hemolymph and hemolymph cells firstly infiltrated the ovariole sheath, from where they invaded the oocyte via two routes: (I) infecting follicular cells, thereby penetrating oocytes after proliferation, and (II) infecting nurse cells, thus entering oocytes following replication. In follicle and nurse cells, the parasites restructured and built large vacuoles to deliver themselves into the oocyte. In the whole process, the parasites were coated with B. mori vitellogenin (BmVg) on their surfaces. To investigate the BmVg effects on TOT, we suppressed its expression and found a dramatic decrease of pathogen load in both ovarioles and eggs, suggesting that BmVg plays a crucial role in the TOT. Thereby, we identified the BmVg domains and parasite spore wall proteins (SWPs) mediating the interaction, and demonstrated that the von Willebrand domain (VWD) interacted with SWP12, SWP26 and SWP30, and the unknown function domain (DUF1943) bound with the SWP30. When disrupting these interactions, we found significant reductions of the pathogen load in both ovarioles and eggs, suggesting that the interplays between BmVg and SWPs were vital for the TOT. In conclusion, our study has elucidated key aspects about the microsporidian TOT and revealed the key factors for understanding the molecular mechanisms underlying this transmission.

Widespread sex dimorphism across single-cell transcriptomes of adult African turquoise killifish tissues

The African turquoise killifish (Nothobranchius furzeri), the shortest-lived vertebrate that can be bred in captivity, is an emerging model organism for aging research. Here, we describe a multitissue, single-cell gene expression atlas of female and male blood, kidney, liver, and spleen. We annotate 22 cell types, define marker genes, and infer differentiation trajectories. We find pervasive sex-dimorphic gene expression across cell types. Sex-dimorphic genes tend to be linked to lipid metabolism, consistent with clear differences in lipid storage in female vs. male turquoise killifish livers. We use machine learning to predict sex using single-cell gene expression and identify potential markers for molecular sex identity. As a proof of principle, we show that our atlas can be used to deconvolute existing bulk RNA sequencing (RNA-seq) data to obtain accurate estimates of cell type proportions. This atlas can be a resource to the community that could be leveraged to develop cell-type-specific expression in transgenic animals.

The DUF1943 and VWD domains endow Vitellogenin from Crassostrea gigas with the agglutination and inhibition ability to microorganism

Vitellogenin (Vg) is the major precursor of the egg-yolk proteins, which mainly acts as an energy reserve molecule for providing nutrients during embryonic development. Vg also plays an immune function in vertebrates such as fish, but there are few studies on the immune function of Vg in invertebrates. In the present study, a Vg homologue (CgVg) was identified and characterized in oyster Crassostrea gigas. There are three domains in the CgVg protein, including a Vitellogenin_N domain, a domain of unknown function 1943 (DUF1943) and a von Willebrand factor type D domain (VWD). The mRNA transcripts of CgVg were detected in all tested tissues with high expression in the gonad, hepatopancreas and haemocytes, which was 466.29-, 117.15- and 57.49-fold (p < 0.01) of that in adductor muscle, respectively. After Vibrio splendidus stimulation, the mRNA expression level of CgVg in haemocytes increased significantly at 6, 12 and 24 h, which was 1.97-, 3.58- and 1.3-fold (p < 0.01) of that in the seawater group, respectively. The immunofluorescence assay showed that positive signals of CgVg protein were mainly located at the cytoplasm of haemocytes. The recombinant protein of DUF1943 domain (rDUF1943) and VWD domain (rVWD) was able to bind lipopolysaccharide (LPS), mannose (MAN), peptidoglycan (PGN) and poly (I:C), as well as Gram-positive bacteria (Staphylococcus aureus and Micrococcus luteus), Gram-negative bacteria (Escherichia coli and V. splendidus) and fungi (Pichia pastoris). rDUF1943 exhibited stronger agglutination activity towards S. aureus, M. luteus, E. coli, V. splendidus and P. pastoris, while agglutination was only observed in the rVWD group towards P. pastoris. The rVWD inhibited the growth of E. coli, S. aureus and V. splendidus, while no antibacterial activity was detected in rDUF1943 group. Collectively, CgVg not only functioned as a pattern recognition receptor (PRR) to bind various microorganisms and PAMPs, but also as an immune effector participating in the clearance of invaders, in which DUF1943 and VWD domain were mainly responsible for agglutinating and inhibiting microorganism respectively.

Immune functions of the Dscam extracellular variable region in Chinese mitten crab

In arthropods, there is only a single copy of Down Syndrome Cell Adhesion Molecule (Dscam) in the genome, but it can exist as numerous splice variants. There are three hypervariable exons in the extracellular domain and one hypervariable exon in the transmembrane domain. In Chinese mitten crab (Eriocheir sinensis), exons 4, 6 and 14 can produce 25, 34 and 18 alternative splice variants, respectively. In this study, through Illumina sequencing, we identified additional splice variants for exons 6 and 14, hence there may be > 50,000 Dscam protein variants. Sequencing of exons 4, 6 and 14 showed that alternative splicing was altered after bacterial stimulation. Therefore, we expressed and purified the extracellular variable region of Dscam (EsDscam-Ig1-Ig7). Exons 4.3, 6.46 and 14.18, three variable exons of the recombinant protein, were randomly selected. The functions of EsDscam-Ig1-Ig7 in immune defences of E. sinensis were subsequently explored. EsDscam-Ig1-Ig7 was discovered to bind to both Gram-positive Staphylococcus aureus and Gram-negative Vibrio parahaemolyticus, but it did not exhibit antibacterial activity. By promoting hemocyte phagocytosis and bacterial removal, EsDscam-Ig1-Ig7 can also shield the host from bacterial infection. The findings highlight the immunological activities of Dscam alternative splicing and reveal the potential for many more Dscam isoforms than were previously predicted in E. sinensis.

Widespread sex-dimorphism across single-cell transcriptomes of adult African turquoise killifish tissues

The African turquoise killifish (Nothobranchius furzeri), the shortest-lived vertebrate that can be bred in captivity, is an emerging model organism to study vertebrate aging. Here we describe the first multi-tissue, single-cell gene expression atlas of female and male turquoise killifish tissues comprising immune and metabolic cells from the blood, kidney, liver, and spleen. We were able to annotate 22 distinct cell types, define associated marker genes, and infer differentiation trajectories. Using this dataset, we found pervasive sex-dimorphic gene expression across cell types, especially in the liver. Sex-dimorphic genes tended to be involved in processes related to lipid metabolism, and indeed, we observed clear differences in lipid storage in female vs. male turquoise killifish livers. Importantly, we use machine-learning to predict sex using single-cell gene expression in our atlas and identify potential transcriptional markers for molecular sex identity in this species. As proof-of-principle, we show that our atlas can be used to deconvolute existing liver bulk RNA-seq data in this species to obtain accurate estimates of cell type proportions across biological conditions. We believe that this single-cell atlas can be a resource to the community that could notably be leveraged to identify cell type-specific genes for cell type-specific expression in transgenic animals.

Egg Yolk Protein Homologs Identified in Live-Bearing Sharks: Co-Opted in the Lecithotrophy-to-Matrotrophy Shift?

Reproductive modes of vertebrates are classified into two major embryonic nutritional types: yolk deposits (i.e., lecithotrophy) and maternal investment (i.e., matrotrophy). Vitellogenin (VTG), a major egg yolk protein synthesized in the female liver, is one of the molecules relevant to the lecithotrophy-to-matrotrophy shift in bony vertebrates. In mammals, all VTG genes are lost following the lecithotrophy-to-matrotrophy shift, and it remains to be elucidated whether the lecithotrophy-to-matrotrophy shift in nonmammalians is also associated with VTG repertoire modification. In this study, we focused on chondrichthyans (cartilaginous fishes)-a vertebrate clade that underwent multiple lecithotrophy-to-matrotrophy shifts. For an exhaustive search of homologs, we performed tissue-by-tissue transcriptome sequencing for two viviparous chondrichthyans, the frilled shark Chlamydoselachus anguineus and the spotless smooth-hound Mustelus griseus, and inferred the molecular phylogeny of VTG and its receptor very low-density lipoprotein receptor (VLDLR), across diverse vertebrates. As a result, we identified either three or four VTG orthologs in chondrichthyans including viviparous species. We also showed that chondrichthyans had two additional VLDLR orthologs previously unrecognized in their unique lineage (designated as VLDLRc2 and VLDLRc3). Notably, VTG gene expression patterns differed in the species studied depending on their reproductive mode; VTGs are broadly expressed in multiple tissues, including the uterus, in the two viviparous sharks, and in addition to the liver. This finding suggests that the chondrichthyans VTGs do not only function as the yolk nutrient but also as the matrotrophic factor. Altogether, our study indicates that the lecithotrophy-to-matrotrophy shift in chondrichthyans was achieved through a distinct evolutionary process from mammals.

A Novel Ig Domain-Containing C-Type Lectin Triggers the Intestine-Hemocyte Axis to Regulate Antibacterial Immunity in Crab

The C-type lectin family with the signature C-type lectin-like domain promotes antibacterial host defense within the animal kingdom. We examined the role of Chinese mitten crab, Eriocheir sinensis (H. Milne-Edwards) (Decapoda: Grapsidae) Ig domain-containing C-type lectin (EsIgLectin), a novel and poorly understood member of the C-type lectin family. EsIgLectin was expressed primarily by both hemocytes (E sinensis) and intestines, with significantly induced mRNA expression on intestinal or hemolymph bacterial infections. As a soluble protein, both its C-type lectin-like domain and the Ig domain were required for bacterial binding, bacterial agglutination, bacterial growth inhibition, and in vivo bacterial clearance. Polymeric EsIgLectin could be constructed via the disulfide bond in the Ig domain, significantly enhancing EsIgLectin antibacterial activity. EsIgLectin promoted bacterial phagocytosis in an Ig domain-dependent manner in hemocytes, while it controlled microbial homeostasis and protected against bacteria-induced inflammation in the intestine. Protein interaction studies revealed that the EsIgLectin Ig domain bound to the first Ig domain of the polymeric Ig receptor, which was essential for EsIgLectin-induced bacterial phagocytosis. The temporal sequence of cell interactions during intestinal inflammation is only beginning to be understood. In this article, we show that hemocyte-derived EsIgLectin entered the intestinal wall at the later phase of intestinal inflammation. Moreover, EsIgLectin protected the host against intestinal and hemolymph infections in a polymeric Ig receptor-dependent manner. Therefore, the EsIgLectin promoted bacterial clearance and protected against inflammatory disease through an independent or synergistic effect of hemocytes and intestines in invertebrates.