The Oxygen Load Supplied during Delivery Room Stabilization of Preterm Infants Modifies the DNA Methylation Profile

Early life epigenetics and childhood outcomes: a scoping review

Epigenetics is the study of changes in gene expression, without a change in the DNA sequence that are potentially heritable. Epigenetic mechanisms such as DNA methylation, histone modifications, and small non-coding RNA (sncRNA) changes have been studied in various childhood disorders. Causal links to maternal health and toxin exposures can introduce epigenetic modifications to the fetal DNA, which can be detected in the cord blood. Cord blood epigenetic modifications provide evidence of in-utero stressors and immediate postnatal changes, which can impact both short and long-term outcomes in children. The mechanisms of these epigenetic changes can be leveraged for prevention, early detection, and intervention, and to discover novel therapeutic modalities in childhood diseases. We report a scoping review of early life epigenetics, the influence of maternal health, maternal toxin, and drug exposures on the fetus, and its impact on perinatal, neonatal, and childhood outcomes. IMPACT STATEMENT: Epigenetic changes such as DNA methylation, histone modification, and non-coding RNA have been implicated in the pathophysiology of various disease processes. The fundamental changes to an offspring's epigenome can begin in utero, impacting the immediate postnatal period, childhood, adolescence, and adulthood. This scoping review summarizes current literature on the impact of early life epigenetics, especially DNA methylation on childhood health outcomes.

Gestational Weight Gain Relates to DNA Methylation in Umbilical Cord, Which, In Turn, Associates with Offspring Obesity-Related Parameters

Excessive gestational weight gain (GWG) has a negative impact on offspring's health. Epigenetic modifications mediate these associations by causing changes in gene expression. We studied the association between GWG and DNA methylation in umbilical cord tissue; and determined whether the DNA methylation and the expression of corresponding annotated genes were associated with obesity-related parameters in offspring at 6 years of age. The methylated CpG sites (CpGs) associated with GWG were identified in umbilical cord tissue by genome-wide DNA methylation (n = 24). Twelve top CpGs were validated in a wider sample by pyrosequencing (n = 87), and the expression of their 5 annotated genes (SETD8, TMEM214, SLIT3, RPTOR, and HOXC8) was assessed by RT-PCR. Pyrosequencing results validated the association of SETD8, SLIT3, and RPTOR methylation with GWG and showed that higher levels of SETD8 and RPTOR methylation and lower levels of SLIT3 methylation relate to a higher risk of obesity in the offspring. The association of SETD8 and SLIT3 gene expression with offspring outcomes paralleled the association of methylation levels in opposite directions. Epigenetic changes in the umbilical cord tissue could explain, in part, the relationship between GWG and offspring obesity risk and be early biomarkers for the prevention of overweight and obesity in childhood.

Scoping Review of Early Toxic Stress and Epigenetic Alterations in the Neonatal Intensive Care Unit

BACKGROUND

Preterm infants are uniquely vulnerable to early toxic stress exposure while in the neonatal intensive care unit (NICU) and also being at risk for suboptimal neurodevelopmental outcomes. However, the complex biological mechanisms responsible for variations in preterm infants' neurodevelopmental outcomes because of early toxic stress exposure in the NICU remain unknown. Innovative preterm behavioral epigenetics research offers a possible mechanism and describes how early toxic stress exposure may lead to epigenetic alterations, potentially affecting short- and long-term outcomes.

OBJECTIVE

The aim of this study was to review the relationships between early toxic stress exposures in the NICU and epigenetic alterations in preterm infants. The measurement of early toxic stress exposure in the NICU and effect of epigenetic alterations on neurodevelopmental outcomes in preterm infants were also examined.

METHODS

We conducted a scoping review of the literature published between January 2011 and December 2021 using databases PubMed, CINAHL, Cochrance Library, PsycINFO, and Web of Science. Primary data-based research that examined epigenetics, stress, and preterm infants or NICU were included.

RESULTS

A total of 13 articles from nine studies were included. DNA methylations of six specific genes were studied in relation to early toxic stress exposure in the NICU: SLC6A4, SLC6A3, OPRMI, NR3C1, HSD11B2, and PLAGL1. These genes are responsible for regulating serotonin, dopamine, and cortisol. Poorer neurodevelopmental outcomes were associated with alterations in DNA methylation of SLC6A4, NR3C1, and HSD11B2. Measurements of early toxic stress exposure in the NICU were inconsistent among the studies.

DISCUSSION

Epigenetic alterations secondary to early toxic stress exposures in the NICU may be associated with future neurodevelopmental outcomes in preterm infants. Common data elements of toxic stress exposure in preterm infants are needed. Identification of the epigenome and mechanisms by which early toxic stress exposure leads to epigenetic alterations in this vulnerable population will provide evidence to design and test individualized intervention.

Oxygenation of the newborn. The impact of one molecule on newborn lives

Hypoxanthine is a purine metabolite which increases during hypoxia and therefore is an indicator of this condition. Further, when hypoxanthine is oxidized to uric acid in the presence of xanthine oxidase, oxygen radicals are generated. This was the theoretical basis for suggesting and studying, beginning in the 1990s, resuscitation of newborn infants with air instead of the traditional 100% O2. These studies demonstrated a 30% reduction in mortality when resuscitation of term and near term infants was carried out with air compared to pure oxygen. The mechanism for this is not fully understood, however the hypoxanthine -xanthine oxidase system increases oxidative stress and plays a role in regulation of the perinatal circulation. Further, hyperoxic resuscitation inhibits mitochondrial function, and one reason may be that genes involved in ATP production are down-regulated. Thus, the study of one single molecule, hypoxanthine, has contributed to the global prevention of an estimated 2-500,000 annual infant deaths.

The quest for optimum oxygenation during newborn delivery room resuscitation: Is it the baby or is it us?

Achieving "normal oxygenation" in sick newborn infants requiring resuscitation is one of the most difficult and incompletely informed practices in neonatal care. Suboptimal oxygenation, whether too little or too much, has profound repercussions, including death. In the last two decades, clinicians have lost equipoise for the use of higher oxygen strategies due to concerns of hyperoxia but emerging evidence suggests that lower oxygen strategies may also be as detrimental, especially in infants with pulmonary pathologies such as those born at the cusp of viability. Practice at the coalface using rapidly evolving recommendations has also uncovered continuing complexities in the quest to achieve optimum oxygenation during the first critical minutes of life. There are adjustable factors, such as the practical impediments to acquiring knowledge, equipment and expertise as well as unadjustable factors, such as inherent infant pathology, that necessitates agile clinical manipulation to "first do no harm". This review will address the deficiencies in knowledge that currently impede our quest to determine the best and safest means to deliver oxygen to sick infants during the first critical minutes of life and suggest practical solutions for current practice while awaiting definitive evidence from large scale, well defined, randomized controlled studies.

Neurodevelopmental outcomes of preterm infants after randomisation to initial resuscitation with lower (FiO2 <0.3) or higher (FiO2 >0.6) initial oxygen levels. An individual patient meta-analysis

OBJECTIVE

To determine the effects of lower (≤0.3) versus higher (≥0.6) initial fractional inspired oxygen (FiO₂) for resuscitation on death and/or neurodevelopmental impairment (NDI) in infants <32 weeks' gestation.

DESIGN

Meta-analysis of individual patient data from three randomised controlled trials.

SETTING

Neonatal intensive care units.

PATIENTS

543 children <32 weeks' gestation.

INTERVENTION

Randomisation at birth to resuscitation with lower (≤0.3) or higher (≥0.6) initial FiO₂.

OUTCOME MEASURES

Primary: death and/or NDI at 2 years of age.Secondary: post-hoc non-randomised observational analysis of death/NDI according to 5-minute oxygen saturation (SpO₂) below or at/above 80%.

RESULTS

By 2 years of age, 46 of 543 (10%) children had died. Of the 497 survivors, 84 (17%) were lost to follow-up. Bayley Scale of Infant Development (third edition) assessments were conducted on 377 children. Initial FiO₂ was not associated with difference in death and/or disability (difference (95% CI) -0.2%, -7% to 7%, p=0.96) or with cognitive scores <85 (2%, -5% to 9%, p=0.5). Five-minute SpO₂ >80% was associated with decreased disability/death (14%, 7% to 21%) and cognitive scores >85 (10%, 3% to 18%, p=0.01). Multinomial regression analysis noted decreased death with 5-minute SpO₂ ≥80% (odds (95% CI) 09.62, 0.98 to 0.96) and gestation (0.52, 0.41 to 0.65), relative to children without death or NDI.

CONCLUSION

Initial FiO₂ was not associated with difference in risk of disability/death at 2 years in infants <32 weeks' gestation but CIs were wide. Substantial benefit or harm cannot be excluded. Larger randomised studies accounting for patient differences, for example, gestation and gender are urgently needed.

Genome-wide DNA methylation profiling in anorexia nervosa discordant identical twins

Up until now, no study has looked specifically at epigenomic landscapes throughout twin samples, discordant for Anorexia nervosa (AN). Our goal was to find evidence to confirm the hypothesis that epigenetic variations play a key role in the aetiology of AN. In this study, we quantified genome-wide patterns of DNA methylation using the Infinium Human DNA Methylation EPIC BeadChip array ("850 K") in DNA samples isolated from whole blood collected from a group of 7 monozygotic twin pairs discordant for AN. Results were then validated performing a genome-wide DNA methylation profiling using DNA extracted from whole blood of a group of non-family-related AN patients and a group of healthy controls. Our first analysis using the twin sample revealed 9 CpGs associated to a gene. The validation analysis showed two statistically significant CpGs with the rank regression method related to two genes associated to metabolic traits, PPP2R2C and CHST1. When doing beta regression, 6 of them showed statistically significant differences, including 3 CpGs associated to genes JAM3, UBAP2L and SYNJ2. Finally, the overall pattern of results shows genetic links to phenotypes which the literature has constantly related to AN, including metabolic and psychological traits. The genes PPP2R2C and CHST1 have both been linked to the metabolic traits type 2 diabetes through GWAS studies. The genes UBAP2L and SYNJ2 have been related to other psychiatric comorbidity.

Oxygen for the delivery room respiratory support of moderate-to-late preterm infants. An international survey of clinical practice from 21 countries

AIM

The aim of this study was to determine clinician opinion regarding oxygen management in moderate-late preterm resuscitation.

METHODS

An anonymous online questionnaire was distributed through email/social messaging platforms to neonatologists in 21 countries (October 2020-March 2021) via REDCap.

RESULTS

Of the 695 respondents, 69% had access to oxygen blenders and 90% had pulse oximeters. Respondents from high-income countries were more likely to have oxygen blenders than those from middle-income countries (72% vs. 66%). Most initiated respiratory support with FiO₂ 0.21 (43%) or 0.3 (36%) but only 45% titrated FiO₂ to target SpO₂ . Most (89%) considered heart rate as a more important indicator of response than SpO₂ . Almost all (96%) supported the need for well-designed trials to examine oxygenation in moderate-late preterm resuscitation.

CONCLUSION

Most clinicians resuscitated moderate-late preterm infants with lower initial FiO₂ but some cannot/will not target SpO₂ or titrate FiO₂ . Most consider heart rate as a more important indicator of infant response than SpO₂ .Large and robust clinical trials examining oxygen use for moderate-late preterm resuscitation, including long-term neurodevelopmental outcomes, are supported amongst clinicians.

Oxygen Toxicity to the Immature Lung-Part II: The Unmet Clinical Need for Causal Therapy

Oxygen toxicity continues to be one of the inevitable injuries to the immature lung. Reactive oxygen species (ROS) production is the initial step leading to lung injury and, subsequently, the development of bronchopulmonary dysplasia (BPD). Today, BPD remains the most important disease burden following preterm delivery and results in life-long restrictions in lung function and further important health sequelae. Despite the tremendous progress in the pathomechanistic understanding derived from preclinical models, the clinical needs for preventive or curative therapies remain unmet. This review summarizes the clinical progress on guiding oxygen delivery to the preterm infant and elaborates future directions of research that need to take into account both hyperoxia and hypoxia as ROS sources and BPD drivers. Many strategies have been tested within clinical trials based on the mechanistic understanding of ROS actions, but most have failed to prove efficacy. The majority of these studies were tested in an era before the latest modes of non-invasive respiratory support and surfactant application were introduced or were not appropriately powered. A comprehensive re-evaluation of enzymatic, antioxidant, and anti-inflammatory therapies to prevent ROS injury is therefore indispensable. Strategies will only succeed if they are applied in a timely and vigorous manner and with the appropriate outcome measures.

Resuscitation with an Intact Cord Enhances Pulmonary Vasodilation and Ventilation with Reduction in Systemic Oxygen Exposure and Oxygen Load in an Asphyxiated Preterm Ovine Model

(1) Background: Optimal initial oxygen (O₂) concentration in preterm neonates is controversial. Our objectives were to compare the effect of delayed cord clamping with ventilation (DCCV) to early cord clamping followed by ventilation (ECCV) on O₂ exposure, gas exchange, and hemodynamics in an asphyxiated preterm ovine model. (2) Methods: Asphyxiated preterm lambs (127-128 d) with heart rate <90 bpm were randomly assigned to DCCV or ECCV. In DCCV, positive pressure ventilation (PPV) was initiated with 30-60% O₂ and titrated based on preductal saturations (SpO₂) with an intact cord for 5 min, followed by clamping. In ECCV, the cord was clamped, and PPV was initiated. (3) Results: Fifteen asphyxiated preterm lambs were randomized to DCCV (N = 7) or ECCV (N = 8). The inspired O₂ (40 ± 20% vs. 60 ± 20%, p < 0.05) and oxygen load (520 (IQR 414-530) vs. 775 (IQR 623-868), p-0.03) in the DCCV group were significantly lower than ECCV. Arterial oxygenation and carbon dioxide (PaCO₂) levels were significantly lower and peak pulmonary blood flow was higher with DCCV. (4) Conclusion: In asphyxiated preterm lambs, resuscitation with an intact cord decreased O₂ exposure load improved ventilation with an increase in peak pulmonary blood flow in the first 5 min.

When to say no to inhaled nitric oxide in neonates?

Inhaled nitric oxide (iNO) was approved for use in critically ill term and near-term neonates (>34 weeks gestational age) in 1999 for hypoxic respiratory failure (HRF) with evidence of pulmonary hypertension. In 2011 and 2014, the National Institutes of Health and American Academy of Pediatrics respectively recommended against the use of iNO in preterm infants <34 weeks. However, these guidelines were based on trials conducted with varying inclusion criteria and outcomes. Recent guidelines from the American Thoracic Society/American Heart Association, the Pediatric Pulmonary Hypertension Network (PPHNet) and European Pediatric Pulmonary Vascular Disease Network recommend the use of iNO in preterm neonates with HRF with confirmed pulmonary hypertension. This review discusses the available evidence for off-label use of iNO. Preterm infants with prolonged rupture of membranes and pulmonary hypoplasia appear to respond to iNO. Similarly, preterm infants with physiology of pulmonary hypertension with extrapulmonary right-to-left shunts may potentially have an oxygenation response to iNO. An overview of relative and absolute contraindications for iNO use in neonates is provided. Absolute contraindications to iNO use include a ductal dependent congenital heart disease where systemic circulation is supported by a right-to-left ductal shunt, severe left ventricular dysfunction and severe congenital methemoglobinemia. In preterm infants, we do not recommend the routine use of iNO in HRF due to parenchymal lung disease without pulmonary hypertension and prophylactic use to prevent bronchopulmonary dysplasia. Future randomized trials evaluating iNO in preterm infants with pulmonary hypertension and/or pulmonary hypoplasia are warranted. (233/250 words).

Oxidative stress biomarkers in the preterm infant

Oxidative stress (OS) plays a key role in the pathophysiology of preterm infants. Accurate assessment of OS remains an analytical challenge that has been partially addressed during the last few decades. A plethora of approaches have been developed to assess preterm biofluids to demonstrate a link postnatally with preterm OS, giving rise to a set of widely employed biomarkers. However, the vast number of different analytic methods and lack of standardization hampers reliable comparison of OS-related biomarkers. In this chapter, we discuss approaches for the study of OS in prematurity with respect to methodologic considerations, the metabolic source of different biomarkers and their role in clinical studies.

Methylation: An Ineluctable Biochemical and Physiological Process Essential to the Transmission of Life

Methylation is a universal biochemical process which covalently adds methyl groups to a variety of molecular targets. It plays a critical role in two major global regulatory mechanisms, epigenetic modifications and imprinting, via methyl tagging on histones and DNA. During reproduction, the two genomes that unite to create a new individual are complementary but not equivalent. Methylation determines the complementary regulatory characteristics of male and female genomes. DNA methylation is executed by methyltransferases that transfer a methyl group from S-adenosylmethionine, the universal methyl donor, to cytosine residues of CG (also designated CpG). Histones are methylated mainly on lysine and arginine residues. The methylation processes regulate the main steps in reproductive physiology: gametogenesis, and early and late embryo development. A focus will be made on the impact of assisted reproductive technology and on the impact of endocrine disruptors (EDCs) via generation of oxidative stress.

Neonatal parenteral nutrition affects the metabolic flow of glucose in newborn and adult male Hartley guinea pigs' liver

Extremely premature birth is associated with a permanent disruption of energy metabolism. The underlying mechanisms are poorly understood. The oxidative stress induced by parenteral nutrition (PN) during the first week of life is suspected to reprogram energy metabolism in the liver. Full-term male Hartley guinea pigs (to isolate PN from prematurity) receiving PN enriched or not with glutathione (to isolate PN effects from PN-induced oxidative stress effects) or an Oral Nutrition (ON) during the first week of life were used. At 1 week (neonatal) and 16 weeks (adult), measurements of liver glutathione (GSH and GSSG) and activities of three key enzymes of energy metabolism (glucokinase (GCK), phosphofructokinase (PFK), and acetyl-CoA carboxylase (ACC)) were performed. Differences between groups were reported if p ≤ 0.05 (Analysis of Variance). At 1 week, compared to ON, PN induced higher GSSG (oxidative stress), higher GCK activity, and lower PFK and ACC activity, the glutathione supplement prevented all PN effects. At 16 weeks, early PN induced lower GSSG (reductive stress) and lower GCK activity, which was prevented by added glutathione, and higher ACC activity independent of glutathione supplement. ACC was negatively associated (r2 = 0.33) with GSSG. Increased nicotinamide adenine dinucleotide phosphate levels confirmed the glucose-6-phosphate accumulation at 1 week, whereas our protocol failed to document lipid accumulation at 16 weeks. In adult male guinea pigs, neonatal exposure to PN affected glutathione metabolism leading to reductive stress (lower GSSG) and an altered metabolic flow of glucose. Partial prevention with glutathione supplementation suggests that, in addition to peroxides, other factors of PN are involved.

Oxygen in the neonatal period: Oxidative stress, oxygen load and epigenetic changes

Preterm infants frequently require positive pressure ventilation and oxygen supplementation in the first minutes after birth. It has been shown that the amount of oxygen provided during stabilization, the oxygen load, if excessive may cause hyperoxia, and oxidative damage to DNA. Epidemiologic studies have associated supplementation with pure oxygen in the first minutes after birth with childhood cancer. Recent studies have shown that the amount of oxygen supplemented to preterm infants after birth modifies the epigenome. Of note, the degree of DNA hyper-or hypomethylation correlates with the oxygen load provided upon stabilization. If these epigenetic modifications would persist, oxygen supplied in the first minutes after birth could have long term consequences. Further studies with a robust power calculation and long-term follow up are needed to bear out the long-term consequences of oxygen supplementation during postnatal stabilization of preterm infants.

Oxygen metabolism and oxygenation of the newborn

The premature infant is to some extent protected from hypoxia, however defense against hyperoxia is poorly developed. The optimal assessment of oxygenation is to measure oxygen delivery and extraction. At the bedside PaO₂ and SpO₂ are approximations of oxygenation at the tissue level. After birth asphyxia it is crucial to know whether or not to give oxygen supplementation, when, how much, and for how long. Oxygen saturation targets in the delivery room have been studied, but the optimal targets might still be unknown because factors like gender and delayed cord clamping influence saturation levels. However, SpO₂ > 80% at 5 min of age is associated with favorable long term outcome in preterm babies. Immature infants most often need oxygen supplementation beyond the delivery room. Predefined saturation levels, and narrow alarm limits together with the total oxygen exposure may impact on development of oxygen related diseases like ROP and BPD. Hyperoxia is a strong trigger for genetic and epigenetic changes, contributing to the development of these conditions and perhaps lifelong changes.

2019 International Consensus on Cardiopulmonary Resuscitation and Emergency Cardiovascular Care Science With Treatment Recommendations: Summary From the Basic Life Support; Advanced Life Support; Pediatric Life Support; Neonatal Life Support; Education, Implementation, and Teams; and First Aid Task Forces

The International Liaison Committee on Resuscitation has initiated a continuous review of new, peer-reviewed, published cardiopulmonary resuscitation science. This is the third annual summary of the International Liaison Committee on Resuscitation International Consensus on Cardiopulmonary Resuscitation and Emergency Cardiovascular Care Science With Treatment Recommendations. It addresses the most recent published resuscitation evidence reviewed by International Liaison Committee on Resuscitation Task Force science experts. This summary addresses the role of cardiac arrest centers and dispatcher-assisted cardiopulmonary resuscitation, the role of extracorporeal cardiopulmonary resuscitation in adults and children, vasopressors in adults, advanced airway interventions in adults and children, targeted temperature management in children after cardiac arrest, initial oxygen concentration during resuscitation of newborns, and interventions for presyncope by first aid providers. Members from 6 International Liaison Committee on Resuscitation task forces have assessed, discussed, and debated the certainty of the evidence on the basis of the Grading of Recommendations, Assessment, Development, and Evaluation criteria, and their statements include consensus treatment recommendations. Insights into the deliberations of the task forces are provided in the Justification and Evidence to Decision Framework Highlights sections. The task forces also listed priority knowledge gaps for further research.

Oxygen radical disease in the newborn, revisited: Oxidative stress and disease in the newborn period

Thirty years ago, there was an emerging appreciation for the significance of oxidative stress in newborn disease. This prompted a renewed interest in the impact of oxygen therapy for the newborn in the delivery room and beyond, especially in premature infants. Today, the complexity of oxidative stress both in normal regulation and pathology is better understood, especially as it relates to neonatal mitochondrial oxidative stress responses to hyperoxia. Mitochondria are recipients of oxidative damage and have a propensity for oxidative self-injury that has been implicated in the pathogenesis of neonatal lung diseases. Similarly, both intrauterine growth restriction (IUGR) and macrosomia are associated with mitochondrial dysfunction and oxidative stress. Additionally, reoxygenation with 100% O₂ in a hypoxic-ischemic newborn lamb model increased the production of pro-inflammatory cytokines in the brain. Moreover, the interplay between inflammation and oxidative stress in the newborn is better understood because of animal studies. Transcriptomic analyses have found a number of genes to be differentially expressed in murine models of bronchopulmonary dysplasia (BPD). Epigenetic changes have also been detected both in animal models of BPD and premature infants exposed to oxygen. Antioxidant therapy to prevent newborn disease has not been very successful; however, new therapeutic principles, like melatonin, are under investigation.

Targeting Oxygen in Term and Preterm Infants Starting at Birth

Transition into the extrauterine world is characterized by a substantial increase in oxygen availability to tissue. Exact oxygen provision may be needed to avoid negative consequences of hypoxia or hyperoxia. For term and near-term infants, it is recommended to start with air and titrate the oxygen supplement to the saturation nomogram. However, oxygen supplementation in infants less than 32 weeks' gestation is an unsolved conundrum. At present, the inspired fraction of oxygen is set according to gestational age and blended to achieve targeted saturations and heart rates. Studies are still needed to overcome uncertainties about oxygen supplementation during preterm stabilization.

Optimal Inspired Fraction of Oxygen in the Delivery Room for Preterm Infants

Postnatal adaptation of preterm infants entails a series of difficulties among which the immaturity of the respiratory system is the most vital. To overcome respiratory insufficiency, caregivers attending in the delivery room use positive pressure ventilation and oxygen. A body of evidence in relation of oxygen management in the delivery room has been accumulated in recent years; however, the optimal initial inspired fraction of oxygen, the time to achieve specific oxygen saturation targets, and oxygen titration have not been yet clearly established. The aim of this review is to update the reader by critically analyzing the most relevant literature.

Oxygen therapy of the newborn from molecular understanding to clinical practice

Oxygen is one of the most critical components of life. Nature has taken billions of years to develop optimal atmospheric oxygen concentrations for human life, evolving from very low, peaking at 30% before reaching 20.95%. There is now increased understanding of the potential toxicity of both too much and too little oxygen, especially for preterm and asphyxiated infants and of the potential and lifelong impact of oxygen exposure, even for a few minutes after birth. In this review, we discuss the contribution of knowledge gleaned from basic science studies and their implication in the care and outcomes of the human infant within the first few minutes of life and afterwards. We emphasize current knowledge gaps and research that is needed to answer a problem that has taken Nature a considerably longer time to resolve.