Cytokines in the oviparity/viviparity transition: evidence of the interleukin-1 system in a species with reproductive bimodality, the lizard Lacerta vivipara

Pro-inflammatory cytokine IL1β1 participates in promoting parturition related pathways in the ovoviviparous teleost black rockfish (Sebastes schlegelii)

Along with the evolution process, the reproductive strategies evolved including oviparity, viviparity and ovoviviparity, to fit the residential environment maximize the survival rate of the off spring. In mammals, the key to the initiation of parturition is the inflammatory response at the maternal-fetal interface. As a pro-inflammatory cytokine, interleukin 1 beta (IL1β) plays an important role in the process of human parturition. While less is known about IL1β1 in teleost parturition, identification of the functions of IL1β1 in inducing the parturition, black rockfish, an ovoviviparity teleost, which provides over 60% nutrition supply for over 50 000 embryos though a placenta like structure during pregnant, was employed as the research model. In the present study, based on the gene cloning, we detected the expression pattern of both Il1b1 and its receptor perinatal period, as well as the localization to the ovary by in situ hybridization. The different expression genes in transcriptomic data of perinatal primary ovarian cells treated with the recombinant IL1β1 (rIL1β1) obtained by prokaryotic expression system were analyzed. Differentially expressed genes, functional enrichment and pathway analysis mainly included immune response, signal transduction and cell death. In summary, our research provides novel insights into the potential role of IL1β1 in the parturition of ovoviviparity teleost.

Evolutionary traits and functional roles of chemokines and their receptors in the male pregnancy of the Syngnathidae

Vertebrates have developed various modes of reproduction, some of which are found in Teleosts. Over 300 species of the Syngnathidae (seahorses, pipefishes and seadragons) exhibit male pregnancies; the males have specialized brood pouches that provide immune protection, nourishment, and oxygen regulation. Chemokines play a vital role at the mammalian maternal-fetal interface; however, their functions in fish reproduction are unclear. This study revealed the evolutionary traits and potential functions of chemokine genes in 22 oviparous, ovoviviparous, and viviparous fish species through comparative genomic analyses. Our results showed that chemokine gene copy numbers and evolutionary rates vary among species with different modes of reproduction. Syngnathidae lost cxcl13 and cxcr5, which are involved in key receptor-ligand pairs for lymphoid organ development. Notably, Syngnathidae have site-specific mutations in cxcl12b and ccl44, suggesting immune function during gestation. Moreover, transcriptome analysis revealed that chemokine gene expression varies among Syngnathidae species with different types of brood pouches, suggesting adaptive variations in chemokine functions among seahorses and their relatives. Furthermore, challenge experiments on seahorse brood pouches revealed a joint immune function of chemokine genes during male pregnancy. This study provides insights into the evolutionary diversity of chemokine genes associated with different reproductive modes in fish.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42995-023-00205-x.

Molecular characterization and expression patterns of glucocorticoid receptors in the viviparous black rockfish Sebastes schlegelii

Glucocorticoid receptors (GRs) are ligand-activated transcription factors associated with anti-inflammation, stress, metabolism and gonadal development. In this study, two gr genes (gr1 and gr2) were cloned and analyzed from a viviparous teleost, black rockfish (Sebastes schlegelii). The phylogenetic analysis of GRs showed that GR1 and GR2 clustered into teleost GR1 and GR2 separately and differed from the GRs of tetrapods or basal ray-finned fishes. Black rockfish GRs possess four modular domains of the nuclear receptor superfamily: an N-terminal domain (NTD), a DNA-binding domain (DBD), a hinge region (HR) and a ligand-binding domain (LBD). Nine conserved amino acid inserts were found in the GR1 DBD, and the ligand cavity-related amino acids of GR1 and GR2 LBD were slightly different. Tissue distribution analysis revealed that grs was widely expressed in various tissues, while cyp11b was mainly expressed in the testis and head kidney. The cyp11b transcripts were localized in the interrenal glands of the head kidney, the main source of cortisol; grs transcripts were detected in oocytes, the follicle layer and the ovarian wall. Histologically, significant blood vessel dilation was observed in the fetal membrane during or after parturition of black rockfish. The highest levels of serum cortisol and ovarian cyp11b mRNA were detected in parturition. In addition, the relative expression level of gr1 was upregulated significantly after delivery, while the levels of gr2 showed no significant change. In addition, in vitro GC treatment inhibited the expression of il1b but significantly upregulated the transcription of il1r1. These data provide evidence that GRs are likely to work as anti-inflammatory factors by inhibiting the functions of pro-inflammatory factors in the parturition of black rockfish.

Inflammation and convergent placenta gene co-option contributed to a novel reproductive tissue

The evolution of pregnancy exposes parental tissues to new, potentially stressful conditions, which can trigger inflammation.¹ Inflammation is costly^2,3 and can induce embryo rejection, which constrains the evolution of pregnancy.¹ In contrast, inflammation can also promote morphological innovation at the maternal-embryonic interface as exemplified by co-option of pro-inflammatory signaling for eutherian embryo implantation.^1,4,5 Given its dual function, inflammation could be a key process explaining how innovations such as pregnancy and placentation evolved many times convergently. Pelvic brooding ricefishes evolved a novel “plug” tissue,^6,7 which forms inside the female gonoduct after spawning, anchors egg-attaching filaments, and enables pelvic brooders to carry eggs externally until hatching.^6,8 Compared to pregnancy, i.e., internal bearing of embryos, external bearing should alleviate constraints on inflammation in the reproductive tract. We thus hypothesized that an ancestral inflammation triggered by the retention of attaching filaments gave rise to pathways orchestrating plug formation. In line with our hypothesis, histological sections of the developing plug revealed signs of gonoduct injuries by egg-attaching filaments in the pelvic brooding ricefish Oryzias eversi. Tissue-specific transcriptomes showed that inflammatory signaling dominates the plug transcriptome and inflammation-induced genes controlling vital processes for plug development such as tissue growth and angiogenesis were overexpressed in the plug. Finally, mammalian placenta genes were enriched in the plug transcriptome, indicating convergent gene co-option for building, attaching, and sustaining a transient tissue in the female reproductive tract. This study highlights the role of gene co-option and suggests that recruiting inflammatory signaling into physiological processes provides a fast-track to evolutionary innovation.

•

Pelvic brooding induces tissue-specific changes in gene expression

•

Inflammatory signaling characterizes transcriptome of the egg-anchoring plug

•

Similar to embryo implantation, the plug likely evolved from an inflammatory response

•

Mammalian placenta genes were independently co-opted into the plug

Sex steroids are correlated with environmental factors and body condition during the reproductive cycle in females of the lizard Sceloporus torquatus

Reproduction is regulated by multiple factors that influence physiology and behavior to ensure the continuity of species. However, more work is needed to examine the complex relationships between environmental factors and endocrine transducers that modulate reproductive cycles, particularly in lizards. Here, we aimed to characterize the variation in plasma sex steroid levels in different stages of the reproductive cycle in the lizard Sceloporus torquatus and assess whether sex steroid levels were related to environmental factors (temperature, photoperiod, precipitation, and relative humidity) and body condition. Plasma concentrations of estradiol (E₂) and progesterone (P₄) from blood samples were quantified by enzyme-linked immunosorbent assay (ELISA) and radioimmunoanalysis (RIA), respectively. Our results indicate that sex steroid concentrations were positively related to follicular development but negatively related to temperature and precipitation. E₂ increased as the follicles grew, and its concentrations were highest in the preovulatory phase. P₄ showed a similar pattern and persisted during pregnancy. Changes in body condition were non-significant and mainly unrelated to the reproductive stage and plasma sex steroids. Our findings indicate that sex steroids change depending on the season and reproductive stage. We observed high concentrations of E₂ and P₄ in the late vitellogenic and preovulatory stages, probably because of their role in promoting vitellogenesis and ovulation. Additionally, we observed that follicular development is correlated with temperature and photoperiod. To better understand the mechanisms underlying reproduction, future studies of captive populations where environmental factors can be manipulated are needed.

Understanding the natural selection of human embryos: blastocyst quality modulates the inflammatory response during the peri-implantation period

PROBLEM

Decidualized cells display an active role during embryo implantation sensing blastocyst quality, allowing the implantation of normal developed blastocysts and preventing the invasion of impaired developed ones. Here, we characterized the immune microenvironment generated by decidualized cells in response to soluble factors secreted by blastocysts that shape the receptive milieu.

METHOD OF STUDY

We used an in vitro model of decidualization based on the Human Endometrial Stromal Cells line (HESC) differentiated with medroxiprogesterone and dibutyryl-cAMP, then treated with human blastocysts-conditioned media (BCM) classified according to their quality.

RESULTS

Decidualized cells treated with BCM from impaired developed blastocysts increased IL-1β production. Next, we evaluated the ability of decidualized cells to modulate other mediators associated with menstruation as chemokines. Decidualized cells responded to stimulation with BCM from impaired developed blastocysts increasing CXCL12 expression and CXCL8 secretion. The modulation of these markers was associated with the recruitment and activation of neutrophils, while regulatory T cells recruitment was restrained. These changes were not observed in the presence of BCM from normal developed blastocysts.

CONCLUSION

Soluble factors released by impaired developed blastocysts induce an exacerbated inflammatory response associated with neutrophils recruitment and activation, providing new clues to understand the molecular basis of the embryo-endometrial dialogue.

A pronounced uterine pro-inflammatory response at parturition is an ancient feature in mammals

Regulating maternal immunity is necessary for successful human pregnancy. Whether this is needed in mammals with less invasive placentation is subject to debate. Indeed, the short gestation times in marsupials have been hypothesized to be due to a lack of immune regulation during pregnancy. Alternatively, the maternal marsupial immune system may be unstimulated in the absence of a highly invasive placenta. Transcripts encoding pro-inflammatory cytokines were found to be overrepresented in the whole uterine transcriptome at terminal pregnancy in the opossum, Monodelphis domestica To investigate this further, immune gene transcripts were quantified throughout opossum gestation. Transcripts encoding pro-inflammatory cytokines remained relatively low during pre- and peri-attachment pregnancy stages. Levels dramatically increased late in gestation, peaking within 12 h prior to parturition. These results mirror the spike of inflammation seen at eutherian parturition but not at attachment or implantation. Our results are consistent with the role of pro-inflammatory cytokines at parturition being an ancient and conserved birth mechanism in therian mammals.

The immunomodulatory role of the hypothalamus-pituitary-gonad axis: Proximate mechanism for reproduction-immune trade offs?

The present review discusses the communication between the hypothalamic-pituitary-gonad (HPG) axis and the immune system of vertebrates, attempting to situate the HPG-immune interaction into the context of life history trade-offs between reproductive and immune functions. More specifically, (i) we review molecular and cellular interactions between hormones of the HPG axis, and, as far as known, the involved mechanisms on immune functions, (ii) we evaluate whether the HPG-immune crosstalk serves as proximate mechanism mediating reproductive-immune trade-offs, and (iii) we ask whether the nature of the HPG-immune interaction is conserved throughout vertebrate evolution, despite the changes in immune functions, reproductive modes, and life histories. In all vertebrate classes studied so far, HPG hormones have immunomodulatory functions, and indications exist that they contribute to reproduction-immunity resource trade-offs, although the very limited information available for most non-mammalian vertebrates makes it difficult to judge how comparable or different the interactions are. There is good evidence that the HPG-immune crosstalk is part of the proximate mechanisms underlying the reproductive-immune trade-offs of vertebrates, but it is only one factor in a complex network of factors and processes. The fact that the HPG-immune interaction is flexible and can adapt to the functional and physiological requirements of specific life histories. Moreover, the assumption of a relatively fixed pattern of HPG influence on immune functions, with, for example, androgens always leading to immunosuppression and estrogens always being immunoprotective, is probably oversimplified, but the HPG-immune interaction can vary depending on the physiological and envoironmental context. Finally, the HPG-immune interaction is not only driven by resource trade-offs, but additional factors such as, for instance, the evolution of viviparity shape this neuroendocrine-immune relationship.

Immunoreactivities of IL-1β and IL-1R in oviduct of Chinese brown frog (Rana dybowskii) during pre-hibernation and the breeding period

The Chinese brown frog (Rana dybowskii) has one special physiological phenomenon, which is that its oviduct goes through expansion prior to hibernation instead of during the breeding period. In this study, we investigated the localization and expression level of interleukin-1 (IL-1β) and its functional membrane receptor type I (IL1R1) proteins in the oviduct of R. dybowskii during pre-hibernation and the breeding period. There were significant differences in both oviductal weight and pipe diameter, with values markedly higher in pre-hibernation than in the breeding period. Histologically, epithelium cells, glandular cells and tubule lumen were identified in the oviduct during pre-hibernation and the breeding period, while sizes of both cell types are larger in the pre-hibernation than those of the breeding period. IL-1β was immunolocalized in the cytoplasm of epithelial and glandular cells in both periods, whereas IL-1R1 was observed in the membrane of epithelial and glandular cells in the breeding period, whereas only in epithelial cells during pre-hibernation. Consistently, the protein levels of IL-1β and IL-1R1 were higher in pre-hibernation as compared to the breeding period. These results suggested that IL-1β may play an important autocrine or paracrine role in oviductal cell proliferation and differentiation of R. dybowskii.

Uterine gene expression in the live-bearing lizard, Chalcides ocellatus, reveals convergence of squamate reptile and mammalian pregnancy mechanisms

Although the morphological and physiological changes involved in pregnancy in live-bearing reptiles are well studied, the genetic mechanisms that underlie these changes are not known. We used the viviparous African Ocellated Skink, Chalcides ocellatus, as a model to identify a near complete gene expression profile associated with pregnancy using RNA-Seq analyses of uterine transcriptomes. Pregnancy in C. ocellatus is associated with upregulation of uterine genes involved with metabolism, cell proliferation and death, and cellular transport. Moreover, there are clear parallels between the genetic processes associated with pregnancy in mammals and Chalcides in expression of genes related to tissue remodeling, angiogenesis, immune system regulation, and nutrient provisioning to the embryo. In particular, the pregnant uterine transcriptome is dominated by expression of proteolytic enzymes that we speculate are involved both with remodeling the chorioallantoic placenta and histotrophy in the omphaloplacenta. Elements of the maternal innate immune system are downregulated in the pregnant uterus, indicating a potential mechanism to avoid rejection of the embryo. We found a downregulation of major histocompatability complex loci and estrogen and progesterone receptors in the pregnant uterus. This pattern is similar to mammals but cannot be explained by the mammalian model. The latter finding provides evidence that pregnancy is controlled by different endocrinological mechanisms in mammals and reptiles. Finally, 88% of the identified genes are expressed in both the pregnant and the nonpregnant uterus, and thus, morphological and physiological changes associated with C. ocellatus pregnancy are likely a result of regulation of genes continually expressed in the uterus rather than the initiation of expression of unique genes.

Innate immune performance and steroid hormone profiles of pregnant versus nonpregnant cottonmouth snakes (Agkistrodon piscivorus)

Squamates (lizards and snakes) have independently evolved viviparity over 100 times, and exhibit a wide range of maternal investment in developing embryos from the extremes of lecithotrophic oviparity to matrotrophic viviparity. This group therefore provides excellent comparative opportunities for studying endocrine and immune involvement during pregnancy, and their possible interactions. We studied the cottonmouth (Agkistrodon piscivorus), since they exhibit limited placentation (e.g., ovoviviparity), allowing comparison with squamate species hypothesized to require considerable maternal immune modulation due to the presence of a more extensive placental connection. Furthermore, the cottonmouth's biennial reproductive cycle provides an opportunity for simultaneously comparing pregnant and non-pregnant females in the wild. We document significantly elevated concentrations of progesterone (P4) and significantly lower concentrations of estradiol (E2) in pregnant females relative to non-pregnant females. Pregnant females had lower plasma bacteria lysis capacity relative to non-pregnant females. This functional measure of innate immunity is a proxy for complement performance, and we also determined significant correlations between P4 and decreased complement performance in pregnant females. These findings are consistent with studies that have determined P4's role in complement modulation during pregnancy in mammals, and thus this study joins a growing number of studies that have demonstrated convergent and/or conserved physiological mechanisms regulating viviparous reproduction in vertebrates.

Cytokine components and mucosal immunity in the oviduct of Xenopus laevis (amphibia, pipidae)

Most studies on the mucosal immunity in female reproductive tissues have been performed in mammals. In all species, apart from their reproductive strategies, immunity in the genital mucosa is required to defend the host against luminal pathogens. In this study we investigated the role of the innate immunity of the oviductal mucosa of Xenopus laevis, an amphibian characterized by external fertilization. In particular we examined the expression and localization of Interleukin-1β (IL1B), Macrophage migration inhibitory factor (MIF) and Interleukin-1 receptor type 1 (IL1R1) in different oviductal portions including an upper glandular region, an intermediate and a lower aglandular region (the ovisac). Tissues were examined by immunohistochemistry and western blot using polyclonal antibodies against human molecules. IL1B, MIF and IL1R1 were all shown in the three oviductal regions examined, albeit with a general increase towards the external environment. A substantial difference among the cytokine components was also observed mainly in the epithelium of the glandular and intermediate regions. Specifically, all three molecules were expressed by the luminal ciliated cells while only IL1R1 was present in the unciliated cells at the bottom of the epithelial ingrowths. The expression of IL1R1 in these cells appeared as a continuous layer separating the epithelium from the underlying tissues. While supporting the role of the innate immune system for host's defense against pathogens, the peculiar distribution of the cytokine components in the oviduct of X. laevis suggests novel immunologic strategies useful to assure gland secretion essential for egg formation and fertilization.

Fine structure of the female reproductive system in a viviparous insect, Glossina morsitans morsitans (Diptera, Glossinidae)

The female reproductive system of the tsetse fly Glossina morsitans morsitans is analysed by scanning electron microscopy (SEM). The study focuses in particular on the choriothete, a peculiar uterine structure involved in the viviparous mode of reproduction of Glossina morsitans morsitans. Under light microscopy, the choriothete appears formed by numerous tongue-like folds projecting towards the uterine lumen and lined by a thin cuticle. SEM analysis highlights for the first time a distinctive new feature that is not visible by traditional histological methods. That is a cuticular covering of the choriothete, which shows numerous thorns in the form of crest-like structures arranged in nearly parallel lines. The role of the choriothete in pregnancy and in larval nourishment is discussed.

Evolution of viviparity and uterine angiogenesis: vascular endothelial growth factor (VEGF) in oviparous and viviparous skinks

During pregnancy, uterine vasculature of live-bearing lizards proliferates to support embryonic growth and development. Vascular endothelial growth factor (VEGF) is the most potent of a suite of growth factors responsible for uterine vascularization in mammals. We have sequenced VEGF mRNA transcripts expressed in the uterus of oviparous and viviparous Australian skinks, and compared uterine VEGF expression in nonreproductive and late-reproductive Saiphos equalis, a fossorial viviparous skink. VEGF sequences differed between phylogenetic groups of skinks, rather than oviparous and viviparous skinks. Two transcripts were identified in the uterus of each species that had the same splice sites as human VEGF(165) and VEGF(189). A third transcript, found only in uterine and testis tissue from S. equalis, had the same splice sites as human VEGF(111). This is the first natural expression of VEGF(111), previously found only in human cultured cells subjected to environmental stress. All the three VEGF transcripts identified showed higher expression in uterus from late-reproductive S. equalis than nonreproductive females. The different angiogenic properties of VEGF transcripts provide a mechanism that may produce the variety of placental complexities observed in viviparous skinks. The presence of VEGF(111) in S. equalis may be an opportunity to investigate the function of this unique transcript in a whole animal system.

Interleukin 1 in Oviductal Tissues of Viviparous, Oviparous, and Ovuliparous Species of Amphibians1

In previous reports, we have shown that interleukin 1 (IL1), a cytokine associated with implantation in mice, is also expressed in reproductive tissues of viviparous squamate reptiles and cartilaginous fishes. In the present study, we investigated the expression of IL1B and its functional membrane receptor type I (IL1R1) in amphibians, a class of vertebrates that is characterized by different reproductive modes, including internal and external fertilization. In particular, we investigated the oviductal tissues of the aplacental viviparous Salamandra lanzai, the oviparous Triturus carnifex, and the ovuliparous Bufo bufo. In immunohistochemistry with anti-human IL1B and IL1R1 polyclonal antibodies we found that in S. lanzai, most cells in the uterine mucosa were immunoreactive for IL1B and IL1R1. In T. carnifex, IL1B and IL1R1 were present in ciliated luminal cells, and there was evidence of IL1B in glandular cells. In B. bufo, the expression of IL1B and IL1R1 was limited to the apical cytoplasm of the ciliated oviductal cells. Western blot analysis showed that a putative mature form of IL1B, similar to that seen in mammals, was present in the oviductal tissues of S. lanzai, whereas different forms, which probably correspond to an inactive pro-IL1B protein, were found in T. carnifex and B. bufo. A band that corresponded to the predicted 80-kDa human IL1R1 was found in S. lanzai and T. carnifex. Although the present study shows that IL1B and IL1R1 expression occurs in all reproductive modes, the differential expression patterns noted between ovuliparity and oviparity and viviparity may reflect the different roles of IL1 in the various reproductive modes.