Genetic control of intra-uterine growth

Downstream targets of the homeobox gene DLX3 are differentially expressed in the placentae of pregnancies affected by human idiopathic fetal growth restriction

Human idiopathic fetal growth restriction (FGR) is associated with placental insufficiency. Previously, we reported that the expression of homeobox gene Distal-less 3 (DLX3) is increased in idiopathic FGR placentae and is a regulator of villous trophoblast differentiation. Here, we identify the downstream targets of DLX3 in trophoblast-derived cell lines. We modelled the high levels of DLX3 in FGR using an over-expression plasmid construct and complemented this using short-interference RNA (siRNA) for inactivation in cultured cells. Using a real-time PCR-based gene profiling, candidate target genes of DLX3 over-expression and inactivation were identified as regulators of trophoblast differentiation; GATA2 and PPARγ. The expression of GATA2 and PPARγ were further assessed in placental tissues and showed increased mRNA and protein levels in FGR-affected tissues compared with gestation-matched controls. We conclude that DLX3 orchestrates the expression of multiple regulators of trophoblast differentiation and that expression of these regulatory genes is abnormal in FGR.

The role of placental homeobox genes in human fetal growth restriction

Fetal growth restriction (FGR) is an adverse pregnancy outcome associated with significant perinatal and paediatric morbidity and mortality, and an increased risk of chronic disease later in adult life. One of the key causes of adverse pregnancy outcome is fetal growth restriction (FGR). While a number of maternal, fetal, and environmental factors are known causes of FGR, the majority of FGR cases remain idiopathic. These idiopathic FGR pregnancies are frequently associated with placental insufficiency, possibly as a result of placental maldevelopment. Understanding the molecular mechanisms of abnormal placental development in idiopathic FGR is, therefore, of increasing importance. Here, we review our understanding of transcriptional control of normal placental development and abnormal placental development associated with human idiopathic FGR. We also assess the potential for understanding transcriptional control as a means for revealing new molecular targets for the detection, diagnosis, and clinical management of idiopathic FGR.

Lack of aneuploidy for chromosomes 15, 16, and 18 in placentas from small-for-gestational-age liveborn infants

OBJECTIVE

The purpose of this study was to investigate the frequency of confined placental mosaicism (CPM) in placentas from liveborn infants.

STUDY DESIGN

A retrospective analysis of 51 placentas from small-for-gestational-age (SGA), live born infants (birthweight below 5th centile), and 45 placentas from normally grown infants at term was performed. Aneuploidy for chromosomes 15, 16, and 18 was analyzed with QF-PCR (polymorphic markers) and FISH (centromeric probes).

RESULTS

No trisomic sample was detected with either method. FISH revealed 1 case of monosomy 16 in the SGA group, which was not confirmed by PCR. On the other hand, PCR analysis showed allelic imbalances, ie, deviation of the 1:1 peak ratio > 20%, in 5 cases (4 in the SGA and 1 in the control group; P = .157).

CONCLUSION

Trisomic CPM in liveborn SGA infants is much less frequent than previously appreciated. The occurrence and eventual biologic significance of the observed allelic imbalances needs to be further investigated.

Epigenetics in reproductive medicine

Imprinted genes comprise a small subset of the genome whose epigenetic reprogramming in the germ line is necessary for subsequent normal embryonic development. This reprogramming and resetting of the imprints, through an erasure/acquisition/maintenance cycle, is a subtle and tightly orchestrated phenomenon, involving specific genomic regions and methylation enzymes. Dysregulation of imprinted genes has indeed been shown to lead to several human disorders as well as to affect placental and fetal growth. There have been numerous and conflicting studies assessing the possible association of imprinting disorders with assisted reproductive techniques. This work analyzes all relevant and available reports with regard to the association between assisted reproductive techniques and imprinting disorders. It also discusses whether this possibly increased risk of imprinting disorders may be linked to specific steps of these reproductive techniques or already present in the gametes of infertile patients. A better understanding of epigenetic reprogramming in the germ line is absolutely necessary both to assess the safety of these methods and of the use of impaired spermatogenesis gametes for assisted reproduction.

Identification of two novel allelic variants of ESX1L in the human placenta: lack of an association with intrauterine growth restriction

Intrauterine growth restriction (IUGR) is a leading cause of neonatal morbidity and mortality. Although epidemiological studies implicate an important role for genetic factors in determining birth weight, few candidate genes for IUGR have been identified. ESX1L, the orthologue of Esx1, is an X chromosome-linked human homeobox gene expressed in the placenta and testis. The present study was undertaken to determine if aberrations in the ESX1L gene were associated with idiopathic IUGR because targeted deletion of Esx1 in the mouse leads to abnormal placental development and consequent IUGR. Genotyping analysis of ESX1L gene was performed on placental samples from 22 normal term and 12 IUGR term fetuses. Two allelic variants were identified, and they contain an insertion and a deletion, respectively, of the same 27 nucleotides in the highly repetitive region of exon-4 that encodes the previously identified 12 contiguous repeats of a unique 9-amino acid motif, PPMAP(V/L)PPG. Thus, the insertion and deletion variants were predicted to code for an aberrant ESX1L protein containing 13 and 11 contiguous repeats, respectively. However, both variants were detectable and evenly distributed in normal as well as IUGR placentae, indicating that these two variants of ESX1L do not contribute to genetic susceptibility to idiopathic IUGR. Furthermore, no single nucleotide polymorphisms were identified, and there was no difference in the level of ESX1L mRNA between control and IUGR placentae. Taken together, these findings provide the first evidence that two allelic variants of ESX1L exist in the human placenta but they are not associated with idiopathic IUGR.

Parental race, birth weight, gestational age, and fetal growth among twin infants in the United States

BACKGROUND

No previous study has examined the association between paternal race and birth weight among twins.

AIMS

To examine the association of parents' race and birth weight among twins.

STUDY DESIGN

Population-based retrospective cohort study to examine the association between parents' race and birth weight, and its two components, gestation duration and fetal growth among four group of infants: both parents blacks (FB-MB), father white and mother black (FW-MB), father black and mother white (FB-MW), and both parents whites (FW-MW), with "risk-free" analysis to control confounding factors.

SUBJECTS

Twin births (304,466 twins) registered in the United States in 1995-1997.

OUTCOME MEASURES

The means of birth weight, gestational age, and birth-weight-for-gestational age z score, and rates of very low birth weight (VLBW, <1500 g), very preterm birth (VPTB, <32 weeks of gestation), and fetal growth restriction (FGR, <10th percentile of z score).

RESULTS

Means of birth weight, gestational age, and z score were 2234.0, 2301.9, 2361.1, and 2433.8, and 35.02, 35.24, 35.65, and 35.78, and -0.136, -0.070, -0.039, and 0.063, respectively, and the rates of VLBW, VPTB, and FGR were 14.5, 12.3, 10.5, and 8.1, and 16.0, 13.0, 11.6, and 9.2, and 12.6, 11.1, 10.8, and 8.7, respectively, in the FB-MB, FW-MB, FB-MW, and FW-MW groups. Excluding subjects with various risk factors by risk-free analysis did not change the results.

CONCLUSIONS

Both parents' races are important determinants of birth weight, gestational age, and fetal growth among twin pregnancies, with higher effect on gestational age and greater maternal influence than paternal influence.

Genomic imprinting and assisted reproduction

Imprinted genes exhibit a parent-of-origin specific pattern of expression. Such genes have been shown to be targets of molecular defects in particular genetic syndromes such as Beckwith-Wiedemann and Angelman syndromes. Recent reports have raised concern about the possibility that assisted reproduction techniques, such as in vitro fertilization or intracytoplasmic sperm injection, might cause genomic imprinting disorders. The number of reported cases of those disorders is still too small to draw firm conclusions and the safety of these widely used assisted reproduction techniques needs to be further evaluated.

Stem cells today: A. Origin and potential of embryo stem cells

The study of embryo stem cells began in 1963, initially using disaggregates of cleaving rabbit and mouse embryos. Their differentiation in vitro was modest, and usually curtailed at best to the formation of trophectoderm cells, which attached to plastic. Rabbit morulae and blastocysts adhered more readily, trophectoderm forming a sheet of cells which was overgrown by stem cells from inner cell mass. Whole-blastocyst cultures on collagen-coated surfaces produced a pile of cells, and its outgrowths included neural, blood, neuronal, phagocytic and many other types of cell. When inner cell mass was freed and cultured intact or as cell disaggregates, lines of embryo stem cells (ES) were established which possessed good rates of cleavage, and immense stability in their secretion of enzymes, morphology and chromosomal complement. Developmental capacities of single mouse embryo stem cells were measured by injecting one or more into a recipient blastocyst, and extent of colonization in resulting chimaeras measured their pluripotency. In mouse, cell clumps were termed embryoid bodies, which produced similar outgrowths as in rabbit. Component cells again differentiated widely, depending to a limited extent on their exposure to various cytokines or substrates. Markers for differentiation or pluripotency were established, which revealed how neural, cardiac, haematological and other ES lines could be established in vitro. These have proved useful to study early differentiation and their use in grafting to sick recipients. Displaying similar properties, human ES cells emerged in the late 1990s. Models for the clinical use of ES cells showed how they colonized rapidly, travelled to target tissues via fetal pathways, differentiated and colonized target organs. No signs of inflammation or tissue damage were noted; injured tissues could be repaired including remyelination, and no cancers were formed. ES cells offer wide therapeutic potentials for humans, although extensive clinical trials are still awaited.