Mechanism Of Vertical Transmission Research Articles

Collateral Damage in the Placenta during Viral Infection in Pregnancy: A Possible Mechanism for Vertical Transmission and an Adverse Pregnancy Outcome.

In mammals, the placenta is a connection between a mother and a new developing organism. This tissue has a protective function against some microorganisms, transports nutrients, and exchanges gases and excretory substances between the mother and the fetus. Placental tissue is mainly composed of chorionic villi functional units called trophoblasts (cytotrophoblasts, the syncytiotrophoblast, and extravillous trophoblasts). However, some viruses have developed mechanisms that help them invade the placenta, causing various conditions such as necrosis, poor perfusion, and membrane rupture which, in turn, can impact the development of the fetus and put the mother's health at risk. In this study, we collected the most relevant information about viral infection during pregnancy which can affect both the mother and the fetus, leading to an increase in the probability of vertical transmission. Knowing these mechanisms could be relevant for new research in the maternal-fetal context and may provide options for new therapeutic targets and biomarkers in fetal prognosis.

Vertical transmission and prevalence of white spot syndrome virus (WSSV) in the wild spawning population of the Indian white shrimp, Penaeus indicus

White spot disease, caused by white spot syndrome virus (WSSV), has historically been the most devastating disease in shrimp aquaculture industry across the world. The mode of virus transmission is the most crucial stage in the dynamics and management of virus infection. This study explored the mechanism of vertical transmission of WSSV in Indian white shrimp, Penaeus indicus, potential native species for domestication and genetic improvement, using quantitative real time PCR (q RT PCR), light and electron microscopy, and in situ hybridization. Wild brooders of P. indicus (n = 2576) were sampled along the South east coast of India, during 2016 to 2021. Of these ∼ 58 % of the brooders were positive for WSSV, and almost 50 % of infected wild brooders were at the various stages of reproductive maturation. WSSV-PCR positive brooders (n = 200) were analysed for vertical WSSV transmission. The q RT PCR studies of reproductive tissues revealed that 61 % (n = 13) of spermatophore, 54 % (n = 28) of immature ovaries and 48 % (n = 27) of ripe ovaries were infected with WSSV. The lowest level of infection was recorded in females with ripe ovaries (6.84 × 101 ± 9.79 × 100 ng genomic DNA) followed by fertilized eggs (1.59 × 102 ± 3.69 × 101 ng genomic DNA), and larvae (nauplius and zoea). The histology of gravid females with high WSSV copies showed pyknotic and karyorrhectic germinal vesicle with degenerated cortical rods. Conversely, the gravid females with low WSSV copies showed fully developed ovary without characteristic signs of WSSV infection. Transmission electron microscopic studies clearly established the presence of WSSV particles in both ovaries and spermatophores. When subjected to in situ hybridization, WSSV-specific signals were observed in connective tissues of spermatophore, although gravid ovary and fertilized eggs were failed to produce WSSV specific signals. The present study provides the first molecular and histological evidence for trans-ovarian vertical transmission of WSSV. Development of disease-free base population being the cornerstone and first step in establishing the breeding program, the present findings could be a basis for development of such programs.

Detection of arboviruses in Aedes aegypti through transovarian analysis: A study in Goiânia, Goiás.

Arboviral diseases are a group of infectious diseases caused by viruses transmitted by arthropods, mainly mosquitoes. These diseases, such as those caused by the dengue (DENV), Zika (ZIKV), chikungunya (CHIKV), and yellow fever (YFV) viruses, have a significant impact worldwide. In this context, entomological surveillance plays a crucial role in the control and prevention of arboviruses by providing essential information on the presence, distribution, and activity of vector mosquitoes. Based on entomological surveillance, transovarian transmission provides information regarding the maintenance and dissemination of arboviruses. The objective of this study was to detect these arboviruses in Goiânia, Goiás, and analyze the occurrence of transovarian transmission. Aedes aegypti eggs were collected from different regions of Goiânia and cultivated under controlled laboratory conditions until the emergence of adult mosquitoes. Adult females were grouped into pools containing their heads and thoraxes. These pools were subsequently evaluated using reverse-transcription quantitative polymerase chain reaction (RT-qPCR) assay. A total of 157 pools (N=1570) were analyzed, with two pools testing positive for CHIKV and one pool testing positive for ZIKV, indicating that the offspring resulting from transovarian transmission are potentially infectious. In summary, the demonstration of the vertical transmission mechanisms of CHIKV and ZIKV in A. aegypti serves as an alert to health authorities, as these diseases are still underreported, and their primary urban vector has likely acquired this capacity, contributing to the dissemination of these infections.

Trypanosoma cruzi Isolates Naturally Adapted to Congenital Transmission Display a Unique Strategy of Transplacental Passage.

Chagas disease is mainly transmitted by vertical transmission (VT) in nonendemic areas and in endemic areas where vector control programs have been successful. For the present study, we isolated natural Trypanosoma cruzi strains vertically transmitted through three generations and proceeded to study their molecular mechanism of VT using mice. No parasitemia was detected in immunocompetent mice, but the parasites were able to induce an immune response and colonize different organs. VT experiments revealed that infection with different strains did not affect mating, pregnancy, or resorption, but despite low parasitemia, VT strains reached the placenta and resulted in higher vertical transmission rates than strains of either moderate or high virulence. While the virulent strain modulated more than 2,500 placental genes, VT strains modulated 150, and only 29 genes are shared between them. VT strains downregulated genes associated with cell division and replication and upregulated immunomodulatory genes, leading to anti-inflammatory responses and tolerance. The virulent strain stimulated a strong proinflammatory immune response, and this molecular footprint correlated with histopathological analyses. We describe a unique placental response regarding the passage of T. cruzi VT isolates across the maternal-fetal interphase, challenging the current knowledge derived mainly from studies of laboratory-adapted or highly virulent strains. IMPORTANCE The main findings of this study are that we determined that there are Trypanosoma cruzi strains adapted to transplacental transmission and completely different from the commonly used laboratory reference strains. This implies a specific strategy for the vertical transmission of Chagas disease. It is impressive that the strains specialized for vertical transmission modify the gene expression of the placenta in a totally different way than the reference strains. In addition, we describe isolates of T. cruzi that cannot be transmitted transplacentally. Taken together, these results open up new insights into the molecular mechanisms of this insect vector-independent transmission form.

ZIKV can infect human term placentas in the absence of maternal factors

Zika virus infection can result in devastating pregnancy outcomes when it crosses the placental barrier. For human pregnancies, the mechanisms of vertical transmission remain enigmatic. Utilizing a human placenta-cotyledon perfusion model, we examined Zika virus exposure in the absence of maternal factors. To distinguish responses related to viral infection vs. recognition, we evaluated cotyledons perfused with either active or inactivated Zika virus. Active Zika virus exposure resulted in infection, cell death and syncytium injury. Pathology corresponded with transcriptional changes related to inflammation and innate immunity. Inactive Zika virus exposure also led to syncytium injury and related changes in gene expression but not cell death. Our observations reveal pathologies and innate immune responses that are dependent on infection or virus placenta interactions independent of productive infection. Importantly, our findings indicate that Zika virus can infect and compromise placentas in the absence of maternal humoral factors that may be protective.

Vertical Transmission of COVID-19 from Mother to Neonate: A Case Report

Vertical transmission of COVID-19 is a rare case and still in debate. Knowledge and evidences regarding vertical transmission are recently emerging. Further research is still required to determine the mechanism of vertical transmission and long-term follow-up is needed to know the effect of the COVID-19 to the mother and child. We report a case of COVID-19 vertical transmission from mother to neonate

Viral Infections During Pregnancy: The Big Challenge Threatening Maternal and Fetal Health.

Viral infections during pregnancy are associated with adverse pregnancy outcomes, including maternal and fetal mortality, pregnancy loss, premature labor, and congenital anomalies. Mammalian gestation encounters an immunological paradox wherein the placenta balances the tolerance of an allogeneic fetus with protection against pathogens. Viruses cannot easily transmit from mother to fetus due to physical and immunological barriers at the maternal-fetal interface posing a restricted threat to the fetus and newborns. Despite this, the unknown strategies utilized by certain viruses could weaken the placental barrier to trigger severe maternal and fetal health issues especially through vertical transmission, which was not fully understood until now. In this review, we summarize diverse aspects of the major viral infections relevant to pregnancy, including the characteristics of pathogenesis, related maternal-fetal complications, and the underlying molecular and cellular mechanisms of vertical transmission. We highlight the fundamental signatures of complex placental defense mechanisms, which will prepare us to fight the next emerging and re-emerging infectious disease in the pregnancy population.

SARS-CoV-2 infection in pregnancy and risk of stillbirth

The COVID-19 pandemic has changed the lives of millions of people across the globe. As of November 2021, WHO has reported more than 250 million confirmed cases of SARS-CoV-2 infection with more than 5 million deaths. Despite the continuous efforts being made by the medical community to address the fundamental questions posed by the SARSCoV-2 infection in pregnant women and its impact over the mother and the offspring. The aim of this paper is to assess the evidence accumulated since the emergence of the pandemic concerning the impact of SARS-CoV-2 infection on the mother and fetus, especially addressing the risks of intrauterine death in SARS-CoV-2 positive mothers. We searched different databases up to November 2021 for variations of the sentence: "SARS-CoV-2 infection and COVID-19 and pregnancy and fetal death, stillbirth, intrauterine death". The changing physiological and immune responses during pregnancy make a pregnant woman more prone to developing severe forms of COVID-19, causing sometimes serious pregnancy complications such as fetal loss. At times mild general symptoms related to COVID-19 can cause serious fetal complications, suggesting that placental changes are responsible for fetal outcome. Infection with non-Delta variant increases the risk of fetal loss in the third trimester two times compared to healthy population, while Delta variant increases this risk four times. The exact mechanism of vertical transmission is still to be established and these aspects need further research especially assessing COVID-19 variant particularities.

Impact of COVID-19 on Pregnancy and Maternal Health: An Update

The current pandemic caused by the novel coronavirus disease 2019 (COVID-19) is spreading at an accelerated rate globally. Global concerns were raised following its discovery in December 2019, as previous similar diseases. Diseases such as the severe acute respiratory syndrome-related coronavirus (SARS-CoV) and the Middle East respiratory syndrome-related coronavirus (MERS-CoV) are known to lead to adverse outcomes in pregnant women and those in early maternal stages, with significantly higher rates of complication and mortality compared to other groups of individuals. The anatomical, physiological, and immunological changes that occur during pregnancy lead to higher risks associated with respiratory infections for pregnant women, as they can directly affect the well-being of pregnant women and infants. Vertical transmission of COVID-19 from mother to child was a concern, as such transmission could endanger a child. Three mechanisms of vertical transmission have been suggested: intrauterine transmission, placental blood transmission, and intrapartum transmission. This review discusses the impact and pathogenicity of COVID-19 on the well-being of pregnant and early maternal women, both the clinical aspect, health aspects, and diagnostic and therapeutic options. It will also discuss the adverse outcomes among pregnant women and newborn infants who contract the disease and the different mechanisms of vertical transmission from infected mother to child. The diagnostic and therapeutic approaches of COVID- 19 that have been recently used have also been highlighted, in addition to the challenges faced by pregnant women who have contracted the virus during the pandemic.

The impact of Zika virus exposure on the placental proteomic profile

Zika virus (ZIKV) infection has caused severe unexpected clinical outcomes in neonates and adults during the recent outbreak in Latin America, particularly in Brazil. Congenital malformations associated with ZIKV have been frequently reported; nevertheless, the mechanism of vertical transmission and the involvement of placental cells remains unclear. In this study, we applied quantitative proteomics analysis in a floating explant model of chorionic villi of human placental tissues incubated with ZIKV and with ZIKV pre-adsorbed with anti-ZIKV envelope protein. Proteomic data are available via ProteomeXchange with identifier PXD025764. Altered levels of proteins were involved in cell proliferation, apoptosis, inflammatory processes, and the integrin-cytoskeleton complex. Antibody-opsonized ZIKV particles differentially modulated the pattern of protein expression in placental cells; this phenomenon may play a pivotal role in determining the course of infection and the role of mixed infections. The expression of specific proteins was also evaluated by immunoperoxidase assays. These data fill gaps in our understanding of early events after ZIKV placental exposure and help identify infection control targets.

Immune Profile of the Normal Maternal-Fetal Interface in Rhesus Macaques and Its Alteration Following Zika Virus Infection.

The maternal decidua is an immunologically complex environment that balances maintenance of immune tolerance to fetal paternal antigens with protection of the fetus against vertical transmission of maternal pathogens. To better understand host immune determinants of congenital infection at the maternal-fetal tissue interface, we performed a comparative analysis of innate and adaptive immune cell subsets in the peripheral blood and decidua of healthy rhesus macaque pregnancies across all trimesters of gestation and determined changes after Zika virus (ZIKV) infection. Using one 28-color and one 18-color polychromatic flow cytometry panel we simultaneously analyzed the frequency, phenotype, activation status and trafficking properties of αβ T, γδ T, iNKT, regulatory T (Treg), NK cells, B lymphocytes, monocytes, macrophages, and dendritic cells (DC). Decidual leukocytes showed a striking enrichment of activated effector memory and tissue-resident memory CD4+ and CD8+ T lymphocytes, CD4+ Tregs, CD56+ NK cells, CD14+CD16+ monocytes, CD206+ tissue-resident macrophages, and a paucity of B lymphocytes when compared to peripheral blood. t-distributed stochastic neighbor embedding (tSNE) revealed unique populations of decidual NK, T, DC and monocyte/macrophage subsets. Principal component analysis showed distinct spatial localization of decidual and circulating leukocytes contributed by NK and CD8+ T lymphocytes, and separation of decidua based on gestational age contributed by memory CD4+ and CD8+ T lymphocytes. Decidua from 10 ZIKV-infected dams obtained 16-56 days post infection at third (n=9) or second (n=1) trimester showed a significant reduction in frequency of activated, CXCR3+, and/or Granzyme B+ memory CD4+ and CD8+ T lymphocytes and γδ T compared to normal decidua. These data suggest that ZIKV induces local immunosuppression with reduced immune recruitment and impaired cytotoxicity. Our study adds to the immune characterization of the maternal-fetal interface in a translational nonhuman primate model of congenital infection and provides novel insight in to putative mechanisms of vertical transmission.

Maternal metabolic syndrome induces liver injury and promotes tumor growth in the offspring

Abstract Objective Obesity is a growing disease entity affecting a third of women of reproductive age. Epidemiological studies show that children of obese mothers suffer from obesity, long-term morbidity and an increased rate of childhood cancers. However, the mechanisms of disease transmission remain unknown. The aim of this study is to test this hypothesis in a mouse model and shed light on the involved mechanisms of vertical transmission. Methods Female mice were fed a high fat or standard diet (HFD/SD) for 16 weeks before being mated with mice fed a normal diet. Corresponding diet was continued until weaning, all offspring were thereafter fed a SD. Metabolic profile, weight gain, liver enzymes and the gut microbiota profile were assessed in the offspring (n = 24). Additional groups of offspring (n = 48) were injected with a carcinogen (diethylnitrosamine) at week two, tumor characteristics were assessed by computed tomography scan at week 36. Results Mothers fed HFD developed obesity and non-alcoholic fatty liver disease (NAFLD). Female offspring of mothers fed HFD gained significantly more weight (+33.7%, p = 0.001), had increased alanine transaminase levels (62 vs 18 IU/L, p = 0.003) and a significantly altered liver histology exemplified by an increased NAFLD activity score (3.8 vs 0.6, p = 0.016). Expression levels of several candidate genes were studied of which FGF21 showed the largest differential expression between HFD and SD offspring (9 vs 1 2^ΔΔCT, p = <0.001). However, epigenetic analysis of FGF21 in the liver revealed no changes in methylation level between HFD and SD offspring. Furthermore, offspring of HFD mothers had a distinctly altered gut microbiome with lower proportions of Bacteroides caccae, Bacteroidales and Parasutterella excrementihominis. Interestingly, the proportion of female offspring developing tumors was significantly higher in offspring of HFD mothers (83 vs 44%, p = 0.011), the average total tumor volume was larger (234 vs 3.5mm3, p = 0.022) and the offspring developed more tumors (3.5 vs 0.6, p = 0.010). Conclusion Maternal obesity promotes liver tumor growth in the offspring, alters metabolic patterns and induces liver suffering in the progeny in a sex-dependent manner. The gut microbiome seems to play a role in this transmission of disease. Yet further research is needed to determine the vectors of transmission and evaluate preventive interventions in obese mothers.

Natural Vertical Transmission of Dengue Virus Serotype 4 in Aedes aegypti Larvae from Urban Areas in Sinaloa, Mexico.

Dengue virus (DENV) is transmitted to humans by the bite of the vector Aedes aegypti. Several researchers have suggested that the mechanism of vertical transmission of DENV in the vector is a key aspect for the prevalence of the virus in the environment and the potentiation of epidemic outbreaks of the disease. In this context and as part of an integrated study of DENV serotypes in mosquitoes of urban areas in Sinaloa, Mexico, the presence of DENV-4 in larval stages of Ae. aegypti was evaluated to demonstrate the vertical transmission of this serotype. In total, 672 larvae of Ae. aegypti were collected in 16 sectors and were grouped into 36 pools, of which 41.66% (15/36 pools) tested positive for DENV-4, with a minimum infection rate = 22.32. The analysis of the obtained sequences showed a 98% similarity to the DENV-4 with sequences previously reported in GenBank. These results show that Ae. aegypti acts as a natural reservoir for DENV-4 in this region.

The Long and Winding Road for Symbiont and Yolk Protein to Host Oocyte.

Many insects are intimately associated with microbial symbionts, which are passed to developing oocytes in the maternal body for ensuring vertical transmission to the next generation. Previous studies uncovered that some symbionts utilize preexisting host's molecular and cellular machineries for targeting oocytes. For example, the major yolk protein vitellogenin (Vg) is massively produced in fat body cells, processed and transported to ovaries, and incorporated into developing oocytes via Vg receptor (VgR)-mediated endocytosis, and some symbiotic bacteria were reported to interact with Vg and migrate to oocytes by hitchhiking the VgR-mediated endocytotic mechanism. In a recent study, Mao et al. (mBio 12:e01142-20, 2020, https://doi.org/10.1128/mBio.01142-20) reported that, in some leafhoppers, a considerable proportion of Vg is incorporated into symbiotic bacteria and translocated into oocytes by hitchhiking the symbiont's vertical transmission mechanism, uncovering the host's cooption of the symbiont's oocyte-targeting machineries and highlighting complicated trajectories toward host-symbiont coevolution and integration.

Rift Valley fever in northern Senegal: Amodelling approach to analyse the processes underlying virus circulation recurrence.

Rift Valley fever (RVF) is endemic in northern Senegal, a Sahelian area characterized by a temporary pond network that drive both RVF mosquito population dynamics and nomadic herd movements. To investigate the mechanisms that explain RVF recurrent circulation, we modelled a realistic epidemiological system at the pond level integrating vector population dynamics, resident and nomadic ruminant herd population dynamics, and nomadic herd movements recorded in Younoufere area. To calibrate the model, serological surveys were performed in 2015–2016 on both resident and nomadic domestic herds in the same area. Mosquito population dynamics were obtained from a published model trained in the same region. Model comparison techniques were used to compare five different scenarios of virus introduction by nomadic herds associated or not with vertical transmission in Aedes vexans. Our serological results confirmed a long lasting RVF endemicity in resident herds (IgG seroprevalence rate of 15.3%, n = 222), and provided the first estimation of RVF IgG seroprevalence in nomadic herds in West Africa (12.4%, n = 660). Multivariate analysis of serological data suggested an amplification of the transmission cycle during the rainy season with a peak of circulation at the end of that season. The best scenario of virus introduction combined yearly introductions of RVFV from 2008 to 2015 (the study period) by nomadic herds, with a proportion of viraemic individuals predicted to be larger in animals arriving during the 2nd half of the rainy season (3.4%). This result is coherent with the IgM prevalence rate (4%) found in nomadic herds sampled during the 2nd half of the rainy season. Although the existence of a vertical transmission mechanism in Aedes cannot be ruled out, our model demonstrates that nomadic movements are sufficient to account for this endemic circulation in northern Senegal.

Highly Efficient Vertical Transmission for Zika Virus in Aedes aegypti after Long Extrinsic Incubation Time

While the Zika virus (ZIKV) 2014–2017 pandemic has subsided, there remains active transmission. Apart from horizontal transmission to humans, the main vector Aedes aegypti can transmit the virus vertically from mother to offspring. Large variation in vertical transmission (VT) efficiency between studies indicates the influence of parameters, which remain to be characterized. To determine the roles of extrinsic incubation time and gonotrophic cycle, we deployed an experimental design that quantifies ZIKV in individual progeny and larvae. We observed an early infection of ovaries that exponentially progressed. We quantified VT rate, filial infection rate, and viral load per infected larvae at 10 days post oral infection (d.p.i.) on the second gonotrophic cycle and at 17 d.p.i. on the second and third gonotrophic cycle. As compared to previous reports that studied pooled samples, we detected a relatively high VT efficiency from 1.79% at 10 d.p.i. and second gonotrophic cycle to 66% at 17 d.p.i. and second gonotrophic cycle. At 17 d.p.i., viral load largely varied and averaged around 800 genomic RNA (gRNA) copies. Longer incubation time and fewer gonotrophic cycles promoted VT. These results shed light on the mechanism of VT, how environmental conditions favor VT, and whether VT can maintain ZIKV circulation.

Silent circulation of dengue virus in Aedes albopictus (Diptera: Culicidae) resulting from natural vertical transmission

Vertical transmission in Aedes aegypti and Aedes albopictus is considered a maintenance mechanism for dengue virus (DENV) during unfavorable conditions and may be implicated in dengue outbreaks. Since DENV infection dynamics vary among wild-type viruses and vector populations, vertical transmission rates can also vary between regions. However, even though São Paulo is the most populous city in the Americas and has experienced major dengue epidemics, natural vertical transmission had never been detected in this area before. Here we confirm and describe for the first time natural vertical transmission of DENV-3 in two pools of male Ae. albopictus from the city of São Paulo. The detection of DENV-3 in years when no human autochthonous cases of this serotype were recorded suggests that silent circulation of DENV-3 is occurring and indicates that green areas may be maintaining serotypes that are not circulating in the human population, possibly by a vertical transmission mechanism.

Implications of vertical transmission of Alphaviruses in Aedes aegypti mosquitoes

Mosquitoes are vectors for epidemic transmission of viruses of public and veterinary health. The mosquito vector is generally infected for life although, unlike the vertebrate counterpart, does not suffer a high fitness cost. Having a vector infected for the length of its life enables routes of viral transmission other than the classic infected bite (horizontal), including sexual (horizontal) and to the progeny (vertical). Vertical transmission is considered a route of transmission that allows for the persistence of the virus during adverse environmental periods (e.g., droughts, cold periods). Because Aedes aegypti and Aedes albopictus eggs are resistant to dessication, it is hypothesised that this attribute could promote arbovirus survival between transmission cycles, playing an important role in maintaining the pathogen. Vertical transmission of arboviruses has been extensively documented for flaviviruses and bunyaviruses. However, there is very little and contradictory reports of vertical transmission of alphaviruses. In this research we establish the mechanisms of vertical transmission of the alphaviruses Semiliki Forest virus (SFV) and Ross river virus (RRV) and its implications in pathogen transmission of future generations. Aedes aegypti mosquitoes were infected with SFV virus in different gonotrophic cycles. Their offspring was then reared and challenged with SFV, RRV and dengue virus (DENV). Offspring from infected parents showed significant reduction in viral load if infected with SFV or RRV but not with DENV. Findings of this research highlight the importance of vertical transmission of alphaviruses in the general arbovirus infectious cycle.

Rice stripe virus hitchhikes the vector insect vitellogenin ligand-receptor pathway for ovary entry.

It is known that plant arboviruses infect insect vector cells by endocytosis; however, the cellular receptors that mediate endocytosis have not been well defined. In our recently published work and this study, by clarifying the vertical transmission mechanism of Rice stripe virus (RSV) in Laodelphax striatellus, we provide a novel paradigm for how arboviruses enter insect germ-line cells. Instead of direct interaction with a viral receptor, the virus binds to a secreted ligand protein, hitchhiking the ligand-receptor pathway to achieve cell entry. Vitellogenin (Vg) is an indispensable protein for embryo development that is synthesized extra-ovarially and taken up by germ-line cells through Vg receptor (VgR)-mediated endocytosis. After revealing that RSV invades L. striatellus ovary by a specific molecular interaction with the insect Vg in haemolymph, this study addressed VgR's function in mediating the RSV invasion of the germarium nurse cells, further confirming the ligand's receptor-mediated viral cell-invasion mechanism. Understanding the viral ovary-entry pathways in vectors will help to find suitable measures to block the trans-generation transmission of the viruses. This article is part of the theme issue 'Biotic signalling sheds light on smart pest management'.

A symbiont's guide to the germline.

Microbial symbioses exhibit astounding adaptations, yet all symbionts face the problem of how to reliably associate with host offspring every generation. A common strategy is vertical transmission, in which symbionts are directly transmitted from the female to her offspring. The diversity of symbionts and vertical transmission mechanisms is as expansive as the diversity of eukaryotic host taxa that house them. However, there are several common themes among these mechanisms based on the degree to which symbionts associate with the host germline during transmission. In this review, we detail three distinct vertical transmission strategies, starting with associations that are transmitted from host somatic cells to offspring somatic cells, either due to lacking a germline or avoiding it. A second strategy involves somatically-localized symbionts that migrate into the germline during host development. The third strategy we discuss is one in which the symbiont maintains continuous association with the germline throughout development. Unexpectedly, the vast majority of documented vertically inherited symbionts rely on the second strategy: soma-to-germline migration. Given that not all eukaryotes contain a sequestered germline and instead produce offspring from somatic stem cell lineages, this soma-to-germline migration is discussed in the context of multicellular evolution. Lastly, as recent genomics data have revealed an abundance of horizontal gene transfer events from symbiotic and non-symbiotic bacteria to host genomes, we discuss their impact on eukaryotic host evolution.