Analysis of Nsdhl-deficient embryos reveals a role for Hedgehog signaling in early placental development

Identification of novel nutrient sensitive human yolk sac functions required for embryogenesis

The human yolk sac (hYS) is essential for embryo nutrient biosynthesis/transport and development. However, there lacks a comprehensive study of hYS nutrient-gene interactions. Here we performed a secondary analysis of hYS transcript profiles (n = 9 samples) to identify nutrient-sensitive hYS genes and regulatory networks, including those that associate with adverse perinatal phenotypes with embryonic origins. Overall, 14.8% highly expressed hYS genes are nutrient-sensitive; the most common nutrient cofactors for hYS genes are metals and B vitamins. Functional analysis of highly expressed hYS genes reveals that nutrient-sensitive hYS genes are more likely to be involved in metabolic functions than hYS genes that are not nutrient-sensitive. Through nutrient-sensitive gene network analysis, we find that four nutrient-sensitive transcription regulators in the hYS (with zinc and/or magnesium cofactors) are predicted to collectively regulate 30.9% of highly expressed hYS genes. Lastly, we identify 117 nutrient-sensitive hYS genes that associate with an adverse perinatal outcome with embryonic origins. Among these, the greatest number of nutrient-sensitive hYS genes are linked to congenital heart defects (n = 54 genes), followed by microcephaly (n = 37). Collectively, our study characterises nutrient-sensitive hYS functions and improves understanding of the ways in which nutrient-gene interactions in the hYS may influence both typical and pathological development.

Defects in placental syncytiotrophoblast cells are a common cause of developmental heart disease

Placental abnormalities have been sporadically implicated as a source of developmental heart defects. Yet it remains unknown how often the placenta is at the root of congenital heart defects (CHDs), and what the cellular mechanisms are that underpin this connection. Here, we selected three mouse mutant lines, Atp11a, Smg9 and Ssr2, that presented with placental and heart defects in a recent phenotyping screen, resulting in embryonic lethality. To dissect phenotype causality, we generated embryo- and trophoblast-specific conditional knockouts for each of these lines. This was facilitated by the establishment of a new transgenic mouse, Sox2-Flp, that enables the efficient generation of trophoblast-specific conditional knockouts. We demonstrate a strictly trophoblast-driven cause of the CHD and embryonic lethality in one of the three lines (Atp11a) and a significant contribution of the placenta to the embryonic phenotypes in another line (Smg9). Importantly, our data reveal defects in the maternal blood-facing syncytiotrophoblast layer as a shared pathology in placentally induced CHD models. This study highlights the placenta as a significant source of developmental heart disorders, insights that will transform our understanding of the vast number of unexplained congenital heart defects.

Fear Stress During Pregnancy Affects Placental m6A-Modifying Enzyme Expression and Epigenetic Modification Levels

As the hub connecting mother and offspring, the placenta’s normal development is vital for fetal growth. Fear stress can cause some structural alterations in the placenta and affect placental development and function. N6-methyladenosine (m6A) is the most common mRNA modification and is involved in regulating the development of the placenta and embryo. There are no reports on the potential role of m6A modification in placental damage caused by fear stress during pregnancy. In this study, we demonstrated that fear stress during pregnancy increases the levels of methylated enzymes (METTL3, METTL14, and WTAP), decreases the levels of demethylase FTO, and increases the overall methylation levels in the placenta of pregnant rats. MeRIP-seq data analysis revealed 22,010 m6A peaks associated with 12,219 genes in the placenta of the model and 21,060 m6A peaks associated with 11,730 genes in the placenta of the control. The peaks were mainly concentrated in the coding region and the 3ʹ untranslated region. In addition, 50 genes with abnormal modification and expression (double aberrant genes) were screened out by combining MeRIP-seq and RNA-seq data. Mefv, Erbb2, and Cgas were selected from 50 double aberrant genes, and MeRIP-qPCR and real-time quantitative polymerase chain reaction were used to verify their modification and expression levels. Our findings suggest that m6A modifications play an important role in placental dysfunction induced by fear stress during pregnancy.

Integrated Analysis of miRNA-mRNA Network Reveals Different Regulatory Patterns in the Endometrium of Meishan and Duroc Sows during Mid-Late Gestation

Simple Summary

Meishan pigs have a lower fetal loss rate during mid-late gestation compared to Duroc pigs. Differentially expressed mRNAs and miRNAs detected in endometrial tissue from Meishan and Duroc sows at mid-late gestation are involved in regulating hormone and oxygen levels, blood vessel development, and developmental processes affecting reproduction. In addition, ssc-miR-503 and ssc-miR-671-5p were shown to target the EGF and ESR1 genes, respectively. These findings provided an important resource for studying embryonic mortality during mid-late gestation in pigs.

Abstract

Embryo loss is a major factor affecting profitability in the pig industry. Embryonic mortality occurs during peri-implantation and mid-late gestation in pigs. Previous investigations have shown that the embryo loss rate in Meishan pigs is significantly lower than in commercial breeds. Most studies have focused on embryonic mortality during early gestation, but little is known about losses during mid-late gestation. In this study, we performed a transcriptome analysis of endometrial tissue in mid-late gestation sows (gestation days 49 and 72) sampled from two breeds (Meishan (MS) and Duroc (DU)) that have different embryo loss rates. We identified 411, 1113, 697, and 327 differentially expressed genes, and 14, 36, 57, and 43 differentially expressed miRNAs in four comparisons (DU49 vs. DU72, DU49 vs. MS49, DU72 vs. MS72, and MS49 vs. MS72), respectively. Subsequently; seven differentially expressed mRNAs and miRNAs were validated using qPCR. Functional analysis suggested the differentially expressed genes and miRNAs target genes mainly involved in regulation of hormone levels, blood vessel development, developmental process involved in reproduction, embryonic placenta development, and the immune system. A network analysis of potential miRNA-gene interactions revealed that differentially expressed miRNAs in Meishan pigs are involved in the response to estradiol and oxygen levels, and affect angiogenesis and blood vessel development. The binding site on ssc-miR-503 for epidermal growth factor (EGF) and the binding site on ssc-miR-671-5p for estrogen receptor α (ESR1) were identified using a dual luciferase assay. The results of this study will enable further exploration of miRNA-mRNA interactions important in pig pregnancy and will help to uncover molecular mechanisms affecting embryonic mortality in pigs during mid-late gestation.

Primary Cilia and Mammalian Hedgehog Signaling

It has been a decade since it was discovered that primary cilia have an essential role in Hedgehog (Hh) signaling in mammals. This discovery came from screens in the mouse that identified a set of genes that are required for both normal Hh signaling and for the formation of primary cilia. Since then, dozens of mouse mutations have been identified that disrupt cilia in a variety of ways and have complex effects on Hedgehog signaling. Here, we summarize the genetic and developmental studies used to deduce how Hedgehog signal transduction is linked to cilia and the complex effects that perturbation of cilia structure can have on Hh signaling. We conclude by describing the current status of our understanding of the cell-type-specific regulation of ciliogenesis and how that determines the ability of cells to respond to Hedgehog ligands.

GLI3 Links Environmental Arsenic Exposure and Human Fetal Growth

Although considerable evidence suggests that in utero arsenic exposure affects children's health, these data are mainly from areas of the world where groundwater arsenic levels far exceed the World Health Organization limit of 10 μg/L. We, and others, have found that more common levels of in utero arsenic exposure may also impact children's health. However, the underlying molecular mechanisms are poorly understood. To address this issue, we analyzed the expression of key developmental genes in fetal placenta in a birth cohort of women using unregulated water supplies in a US region with elevated groundwater arsenic. We identified several genes whose expression associated with maternal arsenic exposure in a fetal sex-specific manner. In particular, expression of the HEDGEHOG pathway component, GLI3, in female placentae was both negatively associated with arsenic exposure and positively associated with infant birth weight. This suggests that modulation of GLI3 in the fetal placenta, and perhaps in other fetal tissues, contributes to arsenic's detrimental effects on fetal growth. We showed previously that arsenic-exposed NIH3T3 cells have reduced GLI3 repressor protein. Together, these studies identify GLI3 as a key signaling node that is affected by arsenic, mediating a subset of its effects on developmental signaling and fetal health.

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In utero arsenic exposure associates with the expression of several key developmental genes in the fetal placenta.

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There is extensive sexual dimorphism in the associations between placental gene expression and in utero arsenic exposure.

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GLI3 expression in the female fetal placenta associates with arsenic exposure and may mediate its effects on fetal growth.

Sonic hedgehog through Gli2 and Gli3 is required for the proper development of placental labyrinth

Sonic hedgehog (Shh) functions as a conserved morphogen in the development of various organs in metazoans ranging from Drosophila to humans. Here, we have investigated the potential roles and underlying mechanisms of Shh signaling in murine placentation. Immunostaining revealed the abundant expression of the main components of Shh pathway in both the trophectoderm of blastocysts and developing placentas. Disruption of Shh led to impaired vascularogenesis of yolk sac, less branching and malformation of placental labyrinth, thereby leading to a robust decrease in capacity of transplacental passages. Moreover, placenta-specific gene incorporation by lentiviral transduction of mouse blastocysts and blastocyst transplantation robustly knocked down the expression of Gli3 and Gli2 in placenta but not in embryos. Finally, Gli3 knockdown in Shh^−/− placentas partially rescued the defects of both yolk sac and placental labyrinth, and robustly restored the capacity of transplacental passages. Gli2 knockdown in Shh^+/− placentas affected neither the capacity of tranplacental passages nor the vascularogenesis of yolk sac, however, it partially phenocopied the labyrinthine defects of Shh^−/− placentas. Taken together, these results uncover that both Shh/Gli2 and Shh/Gli3 signals are required for proper development of murine placentas and are possibly essential for pregnant maintenance.

Analysis of hedgehog signaling in cerebellar granule cell precursors in a conditional Nsdhl allele demonstrates an essential role for cholesterol in postnatal CNS development

NSDHL is a 3β-hydroxysterol dehydrogenase that is involved in the removal of two C-4 methyl groups in one of the later steps of cholesterol biosynthesis. Mutations in the gene encoding the enzyme are responsible for the X-linked, male lethal mouse mutations bare patches and striated, as well as most cases of human CHILD syndrome. Rare, hypomorphic NSDHL mutations are also associated with X-linked intellectual disability in males with CK syndrome. Since hemizygous male mice with Nsdhl mutations die by midgestation, we generated a conditional targeted Nsdhl mutation (Nsdhl(tm1.1Hrm)) to investigate the essential role of cholesterol in the early postnatal CNS. Ablation of Nsdhl in radial glia using GFAP-cre resulted in live-born, normal appearing affected male pups. However, the pups develop overt ataxia by postnatal day 8-10 and die shortly thereafter. Histological abnormalities include progressive loss of cortical and hippocampal neurons, as well as deficits in the proliferation and migration of cerebellar granule precursors and subsequent massive apoptosis of the cerebellar cortex. We replicated the granule cell precursor proliferation defect in vitro and demonstrate that it results from defective signaling by SHH. Furthermore, this defect is almost completely rescued by supplementation of the culture media with exogenous cholesterol, while methylsterol accumulation above the enzymatic block appears to be associated with increased cell death. These data support the absolute requirement for cholesterol synthesis in situ once the blood-brain-barrier forms and cholesterol transport to the fetus is abolished. They further emphasize the complex ramifications of cholesterogenic enzyme deficiency on cellular metabolism.

Lineage specificity of primary cilia in the mouse embryo

Primary cilia are required for vertebrate cells to respond to specific intercellular signals. Here we define when and where primary cilia appear in the mouse embryo using a transgenic line that expresses ARL13B-mCherry in cilia and Centrin 2-GFP in centrosomes. Primary cilia first appear on cells of the epiblast at E6.0 and are subsequently present on all derivatives of the epiblast. In contrast, extraembryonic cells of the visceral endoderm and trophectoderm lineages have centrosomes but no cilia. Stem cell lines derived from embryonic lineages recapitulate the in vivo pattern: epiblast stem cells are ciliated, whereas trophoblast stem cells and extraembryonic endoderm (XEN) stem cells lack cilia. Basal bodies in XEN cells are mature and can form cilia when the AURKA-HDAC6 cilium disassembly pathway is inhibited. The lineage-dependent distribution of cilia is stable throughout much of gestation, defining which cells in the placenta and yolk sac are able to respond to Hedgehog ligands.

Analysis of the Sonic Hedgehog signaling pathway in normal and abnormal bladder development

In this study, we examined the expression of Sonic Hedgehog, Patched, Gli1, Gli2, Gli3 and Myocardin in the developing bladders of male and female normal and megabladder (mgb-/-) mutant mice at embryonic days 12 through 16 by in situ hybridization. This analysis indicated that each member of the Sonic Hedgehog signaling pathway as well as Myocardin displayed distinct temporal and spatial patterns of expression during normal bladder development. In contrast, mgb-/- bladders showed both temporal and spatial changes in the expression of Patched, Gli1 and Gli3 as well as a complete lack of Myocardin expression. These changes occurred primarily in the outer mesenchyme of developing mgb-/- bladders consistent with the development of an amuscular bladder phenotype in these animals. These results provide the first comprehensive analysis of the Sonic Hedgehog signaling pathway during normal bladder development and provide strong evidence that this key signaling cascade is critical in establishing radial patterning in the developing bladder. In addition, the lack of detrusor smooth muscle development observed in mgb-/- mice is associated with bladder-specific temporospatial changes in Sonic Hedgehog signaling coupled with a lack of Myocardin expression that appears to result in altered patterning of the outer mesenchyme and poor initiation and differentiation of smooth muscle cells within this region of the developing bladder.

Disorders of sterol synthesis: beyond Smith-Lemli-Opitz syndrome

Since the discovery in 1993 that Smith-Lemli-Opitz syndrome (SLOS) is a disorder of cholesterol biosynthesis, human disorders associated with additional enzymes involved in the conversion of lanosterol to cholesterol have been identified. This review will focus primarily on the clinical aspects of these disorders, highlighting newly described syndromes, such as SC4MOL deficiency and CK syndrome. We will also provide clinical descriptions of additional cases for extremely rare disorders, such as desmosterolosis. We will compare and contrast the findings with those found in SLOS and briefly discuss possible mechanisms of disease pathogenesis.

Hedgehog signaling in the posterior region of the mouse gastrula suggests manifold roles in the fetal-umbilical connection and posterior morphogenesis

Although many fetal birth defects, particularly those of the body wall and gut, are associated with abnormalities of the umbilical cord, the developmental relationship between these structures is largely obscure. Recently, genetic analysis of mid-gestation mouse embryos revealed that defects in Hedgehog signaling led to omphalocoele, or failure of the body wall to close at the umbilical ring (Matsumaru et al. [ 2011] PLos One 6:e16260). However, systematic spatiotemporal localization of Hedgehog signaling in the allantois, or umbilical precursor tissue, and the surrounding regions has not been documented. Here, a combination of reagents, including the Ptc1:lacZ and Runx1:lacZ reporter mice, immunohistochemistry for Smoothened (Smo), Sonic Hedgehog (Shh), and Indian hedgehog (Ihh), and detailed PECAM-1/Flk-1/Runx-1 analysis, revealed robust Hedgehog signaling in previously undocumented posterior sites over an extended period of time (∼7.0-9.75 dpc). These included the recently described proximal walls of the allantois (Ventral and Dorsal Cuboidal Mesothelia; VCM and DCM, respectively); the ventral embryonic surface continuous with them; hemogenic arterial endothelia; hematopoietic cells; the hindgut; ventral ectodermal ridge (VER); chorionic ectoderm; and the intraplacental yolk sac (IPY), which appeared to be a site of placental hematopoiesis. This map of Hedgehog signaling in the posterior region of the mouse conceptus will provide a valuable foundation upon which to elucidate the origin of many posterior midline abnormalities, especially those of the umbilical cord and associated fetal defects. Developmental Dynamics 240:2175-2193, 2011. © 2011 Wiley-Liss, Inc.

Hypomorphic temperature-sensitive alleles of NSDHL cause CK syndrome

CK syndrome (CKS) is an X-linked recessive intellectual disability syndrome characterized by dysmorphism, cortical brain malformations, and an asthenic build. Through an X chromosome single-nucleotide variant scan in the first reported family, we identified linkage to a 5 Mb region on Xq28. Sequencing of this region detected a segregating 3 bp deletion (c.696_698del [p.Lys232del]) in exon 7 of NAD(P) dependent steroid dehydrogenase-like (NSDHL), a gene that encodes an enzyme in the cholesterol biosynthesis pathway. We also found that males with intellectual disability in another reported family with an NSDHL mutation (c.1098 dup [p.Arg367SerfsX33]) have CKS. These two mutations, which alter protein folding, show temperature-sensitive protein stability and complementation in Erg26-deficient yeast. As described for the allelic disorder CHILD syndrome, cells and cerebrospinal fluid from CKS patients have increased methyl sterol levels. We hypothesize that methyl sterol accumulation, not only cholesterol deficiency, causes CKS, given that cerebrospinal fluid cholesterol, plasma cholesterol, and plasma 24S-hydroxycholesterol levels are normal in males with CKS. In summary, CKS expands the spectrum of cholesterol-related disorders and insight into the role of cholesterol in human development.

Malformation syndromes caused by disorders of cholesterol synthesis

Cholesterol homeostasis is critical for normal growth and development. In addition to being a major membrane lipid, cholesterol has multiple biological functions. These roles include being a precursor molecule for the synthesis of steroid hormones, neuroactive steroids, oxysterols, and bile acids. Cholesterol is also essential for the proper maturation and signaling of hedgehog proteins, and thus cholesterol is critical for embryonic development. After birth, most tissues can obtain cholesterol from either endogenous synthesis or exogenous dietary sources, but prior to birth, the human fetal tissues are dependent on endogenous synthesis. Due to the blood-brain barrier, brain tissue cannot utilize dietary or peripherally produced cholesterol. Generally, inborn errors of cholesterol synthesis lead to both a deficiency of cholesterol and increased levels of potentially bioactive or toxic precursor sterols. Over the past couple of decades, a number of human malformation syndromes have been shown to be due to inborn errors of cholesterol synthesis. Herein, we will review clinical and basic science aspects of Smith-Lemli-Opitz syndrome, desmosterolosis, lathosterolosis, HEM dysplasia, X-linked dominant chondrodysplasia punctata, Congenital Hemidysplasia with Ichthyosiform erythroderma and Limb Defects Syndrome, sterol-C-4 methyloxidase-like deficiency, and Antley-Bixler syndrome.

Significant contributions of the extraembryonic membranes and maternal genotype to the placental pathology in heterozygous Nsdhl deficient female embryos

Mutations in the gene encoding the cholesterol biosynthetic enzyme NSDHL are associated with the X-linked male-lethal bare patches (Bpa) mouse. Mutant male embryos for several Nsdhl alleles die in midgestation with placental insufficiency. We examined here a possible role of the maternal genotype in such placental pathology. Pre-pregnancy plasma cholesterol levels were similar between wild-type (WT) and Bpa(1H)/+ dams fed a standard, cholesterol-free diet. However, there was a marked decrease in cholesterol levels between embryonic day (E)8.5 and E10.5 for both genotypes. Further, there was a significant lag between E11.5 and E13.5 (P = 0.0011) in the recovery of levels in Bpa(1H)/+ dams to their pre-pregnancy values. To investigate possible effects of the maternal genotype on fetal placentation, we generated transgenic mice that expressed human NSDHL and rescued the male lethality of the Bpa(1H) null allele. We then compared placenta area at E10.5 in WT and Bpa(1H)/+ female embryos where the mutant X chromosome was transmitted from a heterozygous mother or a rescued mutant father. In mutant conceptuses, placental areas were approximately 50% less than WT. Surprisingly, expression of Nsdhl in trophoblast lineages of the placenta and yolk sac endoderm, which occurs only from the maternally inherited allele in a female embryo, had the largest effect on placental area (-0.681 mm(2); P < 0.0001). The maternal genotype had a smaller effect, independent of the fetal genotype (-0.283 mm(2); P = 0.024). These data demonstrate significant effects of the mother and fetal membranes on pregnancy outcome, with possible implications for cholesterol homeostasis during human pregnancy.

Genomic changes detected by array CGH in human embryos with developmental defects

Developmental abnormalities of human embryos can be visualized in utero using embryoscopy. Our previous embryoscopic and genetic evaluations detected developmental abnormalities in the majority of both euploid (74%) and aneuploid or polyploid (90%) miscarriages. Since we found the pattern of morphological changes to be similar in euploid and non-euploid embryos, we proposed that lethal submicroscopic changes, not detected by standard chromosome testing, may be responsible for miscarriage of euploid embryos. Whole genome oligo and bacterial artificial chromosome array comparative genome hybridization (CGH) was used to screen for submicroscopic chromosomal changes (DNA copy number variants or CNVs) in 17 euploid embryonic miscarriages, with a range of developmental abnormalities documented by embryoscopy. The CNV breakpoints were refined using a custom array (Agilent) with high resolution coverage of the CNVs. Six unique CNVs, previously not reported, were identified in 5 of the 17 embryos (29% of all cases or 50% of cases studied with higher resolution arrays). All six unique CNVs were <250 kb in size. On the basis of parental array CGH analysis, a de novo origin of a CNV was determined for one embryo (at 13q32.1) and suspected for another (at 10p15.3). Three CNVs, at Xq28, 1q25.3 and 7p14.3, were inherited and a CNV at 17p13.1 was of unknown origin. The genes contained within these unique CNVs will be discussed, with specific reference to rearrangements of syntaxin and tryptophan-aspartic acid (WD) repeat genes. Our report describes for the first time, de novo and inherited unique CNVs in euploid human embryos with specific developmental defects.

Smith-Lemli-Opitz syndrome and inborn errors of cholesterol synthesis: summary of the 2007 SLO/RSH Foundation scientific conference sponsored by the National Institutes of Health

In June 2007, the Smith-Lemli-Opitz/RSH Foundation held a scientific conference hosted jointly by Dr. Robert Steiner from Oregon Health & Science University and Dr. Forbes D. Porter from The Eunice Kennedy Shriver National Institute for Child Health and Human Development, National Institutes of Health. The main goal of this meeting was to promote interaction between scientists with expertise in cholesterol homeostasis, brain cholesterol metabolism, developmental biology, and oxysterol and neurosteroid biochemistry, clinicians researching and treating patients with Smith-Lemli-Opitz syndrome, the patient support organization and families. This report summarizes the presentations and discussions at the conference, represents the conference proceedings, and is intended to foster collaborative research and ultimately improve understanding and treatment of Smith-Lemli-Opitz syndrome and other inborn errors of cholesterol synthesis.

The emergence of hematopoietic stem cells is initiated in the placental vasculature in the absence of circulation

The mouse placenta was unveiled as an important reservoir for hematopoietic stem cells (HSCs), yet the origin of placental HSCs was unknown. By tracking developing HSCs by expression of Runx1-lacZ and CD41, we have found that HSCs emerge in large vessels in the placenta. Analysis of Ncx1(-/-) embryos, which lack a heartbeat, verified that HSC development is initiated in the placental vasculature independent of blood flow. However, fewer CD41+ hematopoietic cells were found in Ncx1(-/-) placentas than in controls, implying that some HSCs/progenitors colonize the placenta via circulation and/or HSC emergence is compromised without blood flow. Importantly, placentas from Ncx1(-/-) embryos possessed equal potential to generate myelo-erythroid and B and T lymphoid cells upon explant culture, verifying intact multilineage hematopoietic potential, characteristic of developing HSCs. These data suggest that, in addition to providing a niche for a large pool of HSCs prior to liver colonization, the placenta is a true site of HSC generation.