IFPA Meeting 2013 Workshop Report II: use of 'omics' in understanding placental development, bioinformatics tools for gene expression analysis, planning and coordination of a placenta research network, placental imaging, evolutionary approaches to understanding pre-eclampsia.

Workshops are an important part of the IFPA annual meeting as they allow for discussion of specialized topics. At the IFPA meeting 2013 twelve themed workshops were presented, five of which are summarized in this report. These workshops related to various aspects of placental biology but collectively covered areas of new technologies for placenta research: 1) use of 'omics' in understanding placental development and pathologies; 2) bioinformatics and use of omics technologies; 3) planning and coordination of a placenta research network; 4) clinical imaging and pathological outcomes; 5) placental evolution.

Placental invasion, preeclampsia risk and adaptive molecular evolution at the origin of the great apes: evidence from genome-wide analyses.

INTRODUCTION: Recent evidence from chimpanzees and gorillas has raised doubts that preeclampsia is a uniquely human disease. The deep extravillous trophoblast (EVT) invasion and spiral artery remodeling that characterizes our placenta (and is abnormal in preeclampsia) is shared within great apes, setting Homininae apart from Hylobatidae and Old World Monkeys, which show much shallower trophoblast invasion and limited spiral artery remodeling. We hypothesize that the evolution of a more invasive placenta in the lineage ancestral to the great apes involved positive selection on genes crucial to EVT invasion and spiral artery remodeling. Furthermore, identification of placentally-expressed genes under selection in this lineage may identify novel genes involved in placental development. METHODS: We tested for positive selection in approximately 18,000 genes using the ratio of non-synonymous to synonymous amino acid substitution for protein-coding DNA. DAVID Bioinformatics Resources identified biological processes enriched in positively selected genes, including processes related to EVT invasion and spiral artery remodeling. RESULTS: Analyses revealed 295 and 264 genes under significant positive selection on the branches ancestral to Hominidae (Human, Chimp, Gorilla, Orangutan) and Homininae (Human, Chimp, Gorilla), respectively. Gene ontology analysis of these gene sets demonstrated significant enrichments for several functional gene clusters relevant to preeclampsia risk, and sets of placentally-expressed genes that have been linked with preeclampsia and/or trophoblast invasion in other studies. CONCLUSION: Our study represents a novel approach to the identification of candidate genes and amino acid residues involved in placental pathologies by implicating them in the evolution of highly-invasive placenta.

Divergent patterns of diversification in courtship and genitalic characters of Timema walking-sticks.

Understanding the patterns of diversification in sexual traits and the selection underlying such diversification represents a major unresolved question in evolutionary biology. We examined the phylogenetic diversification for courtship and external genitalic characters across ten species of Timema walking-sticks, to infer the tempos and modes of character change in these sexual traits and to draw inferences regarding the selective pressures underlying speciation and diversification in this clade. Rates of inferred change in male courtship behaviours were proportional to speciation events, but male external genitalic structures showed a pattern of continuous change across evolutionary time, with divergence proportional to branch lengths. These findings suggest that diversification of courtship behaviour is mediated by processes that occur in association with speciation, whereas diversification of genitalia occurs more or less continuously, most likely driven by forces of sexual selection.

Phylogenetic evidence for early hemochorial placentation in eutheria.

The eutherian placenta is remarkable for its structural and functional variability. In order to construct and test comparative hypotheses relating ecological, behavioral and physiological traits to placental characteristics it is first necessary to reconstruct the historical course of placental evolution. Previous attempts to do so have yielded inconsistent results, particularly with respect to the early evolution of structural relationships between fetal and maternal circulatory systems. Here, we bring a battery of phylogenetic methods - including parsimony, likelihood and Bayesian approaches - to bear on the question of placental evolution. All of these approaches are consistent in indicating that highly invasive hemochorial placentation, as found in human beings and numerous other taxa, was an early evolutionary innovation present in the most ancient ancestors of the living placental mammals.

Placental invasiveness and brain-body allometry in eutherian mammals.

Brain growth is a key trait in the evolution of mammalian life history. Brain development should be mediated by placentation, which determines patterns of resource transfer from mothers to fetal offspring. Eutherian placentation varies in the extent to which a maternal barrier separates fetal tissues from maternal blood. We demonstrate here that more invasive forms of placentation are associated with substantially steeper brain-body allometry, faster prenatal brain growth and slower prenatal body growth. On the basis of the physiological literature we suggest a simple mechanism for these differences: in species with invasive placentation, where the placenta is bathed directly in maternal blood, fatty acids essential for brain development can be readily extracted by the fetus, but in species with less invasive placentation they must be synthesized by the fetus. Hence, with regard to brain-body allometry and prenatal growth patterns, eutherian mammals are structured into distinct groups differing in placental invasiveness.