Sustained Physiological Stretch Induces Abdominal Skin Growth in Pregnancy.

Supraphysiological stretches are exploited in skin expanders to induce tissue growth for autologous implants. As pregnancy is associated with large levels of sustained stretch, we investigated whether skin growth occurs in pregnancy. Therefore, we combined a mechanical model of skin and the observations from suction experiments on several body locations of five pregnant women at different gestational ages. The measurements show a continuous increase in stiffness, with the largest change observed during the last trimester. A comparison with numerical simulations indicates that the measured increase in skin stiffness is far below the level expected for the corresponding deformation of abdominal skin. A new set of simulations accounting for growth could rationalize all observations. The predicted amount of tissue growth corresponds to approximately 40% area increase before delivery. The results of the simulations also offered the opportunity to investigate the biophysical cues present in abdominal skin along gestation and to compare them with those arising in skin expanders. Alterations of the skin mechanome were quantified, including tissue stiffness, hydrostatic and osmotic pressure of the interstitial fluid, its flow velocity and electrical potential. The comparison between pregnancy and skin expansion highlights similarities as well as differences possibly influencing growth and remodeling.

Sequential activation of Notch and Grainyhead gives apoptotic competence to Abdominal-B expressing larval neuroblasts in Drosophila Central nervous system.

Neural circuitry for mating and reproduction resides within the terminal segments of central nervous system (CNS) which express Hox paralogous group 9-13 (in vertebrates) or Abdominal-B (Abd-B) in Drosophila. Terminal neuroblasts (NBs) in A8-A10 segments of Drosophila larval CNS are subdivided into two groups based on expression of transcription factor Doublesex (Dsx). While the sex specific fate of Dsx-positive NBs is well investigated, the fate of Dsx-negative NBs is not known so far. Our studies with Dsx-negative NBs suggests that these cells, like their abdominal counterparts (in A3-A7 segments) use Hox, Grainyhead (Grh) and Notch to undergo cell death during larval development. This cell death also happens by transcriptionally activating RHG family of apoptotic genes through a common apoptotic enhancer in early to mid L3 stages. However, unlike abdominal NBs (in A3-A7 segments) which use increasing levels of resident Hox factor Abdominal-A (Abd-A) as an apoptosis trigger, Dsx-negative NBs (in A8-A10 segments) keep the levels of resident Hox factor Abd-B constant. These cells instead utilize increasing levels of the temporal transcription factor Grh and a rise in Notch activity to gain apoptotic competence. Biochemical and in vivo analysis suggest that Abdominal-A and Grh binding motifs in the common apoptotic enhancer also function as Abdominal-B and Grh binding motifs and maintains the enhancer activity in A8-A10 NBs. Finally, the deletion of this enhancer by the CRISPR-Cas9 method blocks the apoptosis of Dsx-negative NBs. These results highlight the fact that Hox dependent NB apoptosis in abdominal and terminal regions utilizes common molecular players (Hox, Grh and Notch), but seems to have evolved different molecular strategies to pattern CNS.

Combination of "Markers" and the Consequent Importance of Fetal Abdominal Circumference in the First Trimester for Predicting Complications Specific to Monochorionic Twin Pregnancies.

BACKGROUND: Multifetal pregnancies are considered high-risk pregnancies compared to singleton pregnancies. Monochorionic diamniotic (MCDA) twin pregnancies tend to have a more complicated intrauterine course than their dichorionic counterparts. The most common complications are twin-to-twin transfusion syndrome (TTTS), selective fetal growth restriction (sFGR), and unexplained intrauterine fetal demise (IUFD). Early recognition of pregnancies at risk of developing complications will be helpful for counselling the parents and preparing them for necessary interventions in case a complication arises. OBJECTIVES: The aim of our study was to assess the role of discordant crown-rump length (dCRL), discordant nuchal translucency (dNT), and discordant abdominal circumference (dAC) measurements in isolation and in combination at the 11-13+6 weeks' scan in predicting the development of TTTS, sFGR, and IUFD. METHODS: All MCDA twin pregnancies with structurally normal, both live fetuses at the 11-13+6 weeks' scan were followed up by FMF (Fetal Medicine Foundation)-certified operators for development of TTTS, sFGR, and single/double IUFD until delivery. Discordance of CRL, NT, and AC of more than or equal to 10% was considered a "marker," and its presence was correlated with the occurrence of specific antenatal complications, i.e., TTTS, sFGR, and single or double IUFD. RESULTS: Combination of two markers predicted MCDA-related complications in the majority of cases (70.8% positive predictive value). Combination of dNT and dAC was the strongest predictor (80% positive predictive value). CONCLUSIONS: In our population of MC twin pregnancies, dCRL, dNT, and dAC at the 11+0-13+6 weeks' scan, in isolation, had a low predictive value for antenatal complications, i.e., TTTS, sFGR, and single/double IUFD. However, the presence of at least two markers in the first trimester could predict complications in the majority of these pregnancies. The combination of dNT and dAC appears to be the best.

Evolutionary origin and functioning of pregenital abdominal outgrowths in a viviparous insect, Arixenia esau.

Although pregenital abdominal outgrowths occur only rarely in pterygote insects, they are interesting from the evolutionary viewpoint because of their potential homology to wings. Our previous studies of early development of an epizoic dermapteran, Arixenia esau revealed that abdominal segments of the advanced embryos and larvae, growing inside a mother's uterus, are equipped with paired serial outgrowths. Here, we focus on the origin and functioning of these outgrowths. We demonstrate that they bud from the lateral parts of the abdominal nota, persist till the end of intrauterine development, and remain in contact with the uterus wall. We also show that the bundles of muscle fibers associated with the abdominal outgrowths may facilitate flow of the haemolymph from the outgrowths' lumen to the larval body cavity. Following completion of the intrauterine development, abdominal outgrowths are shed together with the larval cuticle during the first molt after the larva birth. Using immunohistochemical and biochemical approaches, we demonstrate that the Arixenia abdominal outgrowths represent an evolutionary novelty, presumably related to intrauterine development, and suggest that they are not related to serial wing homologs.

Theoretical considerations in determining allometric growth within instars of crustaceans, with special reference to Americamysis bahia.

Allometry in crustaceans is typically considered growth over several instars primarily because crustaceans are presumed to grow only during ecdysis (discontinuous growth). Using theoretical distributions of the sizes of two morphometric variables over several instars, four theoretical instar allometry models are postulated: continuous allometry (indiscrete and discrete); discontinuous allometry (indiscrete and discrete); mixed allometry (simple or complex); and two-rate continuous allometry. The estimates of proportions of allometry within the instars are determined using Y = f(X) and X = f(Y) for variables X and Y. The amount of allometry in each variable is estimated using the mean ± standard deviation on the independent variable. Application of these theoretical instar allometry models using carapace and abdomen sizes in six instars indicates Americamysis bahia experiences two-rate continuous allometry, rather than "traditional" discontinuous allometry, with 85% or more of total growth occurring in the intermolt phase, and with the abdomen accounting for about 60% of the expansion.

Diversity of dermal fibroblasts as major determinant of variability in cell reprogramming.

Induced pluripotent stem cells (iPSCs) are adult somatic cells genetically reprogrammed to an embryonic stem cell-like state. Notwithstanding their autologous origin and their potential to differentiate towards cells of all three germ layers, iPSC reprogramming is still affected by low efficiency. As dermal fibroblast is the most used human cell for reprogramming, we hypothesize that the variability in reprogramming is, at least partially, because of the skin fibroblasts used. Human dermal fibroblasts harvested from five different anatomical sites (neck, breast, arm, abdomen and thigh) were cultured and their morphology, proliferation, apoptotic rate, ability to migrate, expression of mesenchymal or epithelial markers, differentiation potential and production of growth factors were evaluated in vitro. Additionally, gene expression analysis was performed by real-time PCR including genes typically expressed by mesenchymal cells. Finally, fibroblasts isolated from different anatomic sites were reprogrammed to iPSCs by integration-free method. Intriguingly, while the morphology of fibroblasts derived from different anatomic sites differed only slightly, other features, known to affect cell reprogramming, varied greatly and in accordance with anatomic site of origin. Accordingly, difference also emerged in fibroblasts readiness to respond to reprogramming and ability to form colonies. Therefore, as fibroblasts derived from different anatomic sites preserve positional memory, it is of great importance to accurately evaluate and select dermal fibroblast population prior to induce reprogramming.

Zelda and the maternal-to-zygotic transition in cockroaches.

In the endopterygote Drosophila melanogaster, Zelda is an activator of the zygotic genome during the maternal-to-zygotic transition (MZT). Zelda binds cis-regulatory elements (TAGteam heptamers), making chromatin accessible for gene transcription. Zelda has been studied in other endopterygotes: Apis mellifera and Tribolium castaneum, and the paraneopteran Rhodnius prolixus. We studied Zelda in the cockroach Blattella germanica, a hemimetabolan, short germ-band, and polyneopteran species. B. germanica Zelda has the complete set of functional domains, which is typical of species displaying ancestral features concerning embryogenesis. Interestingly, we found D. melanogaster TAGteam heptamers in the B. germanica genome. The canonical one, CAGGTAG, is present at a similar proportion in the genome of these two species and in the genome of other insects, suggesting that the genome admits as many CAGGTAG motifs as its length allows. Zelda-depleted embryos of B. germanica show defects involving blastoderm formation and abdomen development, and genes contributing to these processes are down-regulated. We conclude that in B. germanica, Zelda strictly activates the zygotic genome, within the MZT, a role conserved in more derived endopterygote insects. In B. germanica, zelda is expressed during MZT, whereas in D. melanogaster and T. castaneum it is expressed beyond this transition. In these species and A. mellifera, Zelda has functions even in postembryonic development. The expansion of zelda expression beyond the MZT in endopterygotes might be related with the evolutionary innovation of holometabolan metamorphosis. DATABASES: The RNA-seq datasets of B. germanica, D. melanogaster, and T. castaneum are accessible at the GEO databases GSE99785, GSE18068, GSE63770, and GSE84253. In addition, the RNA-seq library from T. castaneum adult females is available at SRA: SRX021963. The B. germanica reference genome is available as BioProject PRJNA203136.

Ultrasonographic appearance and measurement of abdominal structures in healthy Capuchin monkeys (Sapajus spp.).

BACKGROUND: Previous ultrasonographic studies of Sapajus apella to determine the normal anatomy and physiology are incomplete. The aim of this study was to determine normal ultrasonographic appearance and measurements of all abdominal organs and structures of interest. METHODS: Twelve adult monkeys were recruited considered healthy on the basis of history, physical examination, and general blood work. To avoid additional anesthesia, the ultrasonographic examinations were performed during routine screening, annually scheduled by the Unit of Cognitive Primatology & Primate Center, CNR-Rome, where the animals were housed. Ultrasound data were processed offline by two experienced ultrasonographers. RESULTS: Topography, morphology and echostructure were described for almost all organs and descriptive statistics were provided. CONCLUSION: To the author's knowledge, this is the most complete ultrasonographic study in Capuchin monkeys.

Isolation functional characterization of allatotropin receptor from the cotton bollworm, Helicoverpa armigera.

Insect allatotropin (AT) plays multi-functions including regulation of juvenile hormone synthesis, growth, development and reproduction. In the present study, the full-length cDNA encoding the AT receptor was cloned from the brain of Helicoverpa armigera (Helar-ATR). The ORF of Helar-ATR exhibited the characteristic seven transmembrane domains of the G protein-coupled receptor (GPCR) and was close to the ATR of Manduca sexta in the phylogenetic tree. The Helar-ATR expressed in vertebrate cell lines can be activated by Helar-AT and each Helar-ATL in a dose-responsive manner, in the following order: Helar-ATLI > Helar-ATLII > Helar-AT > Helar-ATLIII. Helar-ATLI and Helar-ATLII represented the functional ligands to Helar-ATR in vitro, while Helar-AT and Helar-ATLIII behaved as partial agonists. The in vitro functional analysis suggested that the Helar-ATR signal was mainly coupled with elevated levels of Ca2+ and independent of cAMP levels. Helar-ATR mRNA in larvae showed the highest level in the brain, followed by the thorax ganglion, abdomen ganglion, fat body and midgut. Helar-ATR mRNA levels in the complex of the brain-thoracic-abdomen ganglion on the 2nd day of the larval stage and during later pupal stages were observed to be relatively higher than in the wandering and early pupal stages.

Validation of Reference Charts for Mid-Trimester Fetal Biometry.

OBJECTIVE: The aim of our study was to assess charts proposed for international use in the Intergrowth-21st Project. METHODS: Ultrasound data were collected from 43,923 healthy singleton pregnancies examined at 18-23 weeks of gestation in the Netherlands. Fetal measurements were converted into Z-scores using previous and current Dutch reference charts and Intergrowth charts. The distributions of the Z-scores were compared with the expected standard normal distribution. RESULTS: In the Dutch population, Intergrowth curves perform well for head circumference and biparietal diameter, but not for abdominal circumference (AC, Z- score = 0.43) and femur length (FL, Z-score = 0.26). Similar findings have been reported in other European countries. Compared with the population in the Intergrowth study, Dutch women are relatively tall (170 vs. 162 cm) and sturdy (67 vs. 61 kg) with a moderately high BMI. Maternal size, in particular maternal height, is positively correlated with birthweight. CONCLUSIONS: Whilst the establishment of the Intergrowth charts is an important step towards worldwide uniformity, for now locally derived charts still perform better, especially for AC and FL. Results from our validation study indicate that distinction between normal and pathologically small babies may be improved by taking maternal size into account.

Morphogenesis of serial abdominal outgrowths during development of the viviparous dermapteran, Arixenia esau (Insecta, Dermaptera).

The embryos and first instar larvae of the epizoic earwig, Arixenia esau, develop sequentially in two different compartments of the female reproductive system, that is ovarian follicles and the lateral oviducts (the uterus). Here we show that the second (intrauterine) phase of development consists of three physiologically disparate stages: early embryos (before dorsal closure, surrounded by an egg envelope), late embryos (after dorsal closure, surrounded by an egg envelope) and the first instar larvae (after "hatching" from an egg envelope). Early and late embryos float in the fluid filling the uterus, whereas the first instar larvae develop attached to the uterus wall. Our analyses revealed also that in Arixenia serial multilobed outgrowths develop on dorso-lateral aspects of all abdominal segments. At the onset of the third developmental stage and after liberation from an egg envelope, these outgrowths (or more precisely their lobes) adhere to the epithelium lining the uterus, forming a series of small contact sites, where the mother and embryo tissues are separated only by a thin, presumably permeable, embryonic cuticle. We suggest that all these contact sites collectively constitute a dispersed placenta-like organ involved in the nourishment of the embryo.

The Association of Maternal Age With Fetal Growth and Newborn Measures: The Mumbai Maternal Nutrition Project (MMNP).

BACKGROUND: Young maternal age is associated with poorer birth outcomes, but the mechanisms are incompletely understood. Using data from a prospective cohort of pregnant women living in Mumbai slums, India, we tested whether lower maternal age was associated with adverse fetal growth. METHODS: Fetal crown-rump length (CRL) was recorded at a median (interquartile range, IQR) of 10 weeks' gestation (9-10 weeks). Head circumference (HC), biparietal diameter (BPD), femur length (FL), and abdominal circumference (AC) were recorded at 19 (19-20) and 29 (28-30) weeks. Newborns were measured at a median (IQR) of 2 days (1-3 days) from delivery. Gestation was assessed using prospectively collected menstrual period dates. RESULTS: The sample comprised 1653 singleton fetuses without major congenital abnormalities, of whom 1360 had newborn measurements. Fetuses of younger mothers had smaller CRL (0.01 standard deviation [SD] per year of maternal age; 95% confidence interval CI: 0.00-0.02 1 ; P = .04), and smaller HC, FL, and AC at subsequent visits. Fetal growth of HC (0.04 cm; 95% CI: 0.02-0.05; P < .001), BPD (0.01 cm; 95% CI: 0.00-0.01; P = .009), FL (0.04 cm; 95% CI: 0.02-0.06; P < .001), and AC (0.01 cm; 95% CI: 0.00-0.01; P = .003) up to the third trimester increased with maternal age. Skinfolds, head, and mid-upper arm circumferences were smaller in newborns of younger mothers. Adjusting for maternal prepregnancy socioeconomic status, body mass index, height, and parity attenuated the associations between maternal age and newborn size but did not change those with fetal biometry. CONCLUSION: Fetuses of younger mothers were smaller from the first trimester onward and grew slower, independently of known confounding factors.

The Dachsous/Fat/Four-Jointed Pathway Directs the Uniform Axial Orientation of Epithelial Cells in the Drosophila Abdomen.

The achievement of the final form of an individual requires not only the control of cell size and differentiation but also integrative directional cues to instruct cell movements, positions, and orientations. In Drosophila, the adult epidermis of the abdomen is created de novo by histoblasts. As these expand and fuse, they uniformly orient along the anteroposterior axis. We found that the Dachsous/Fat/Four-jointed (Ds/Ft/Fj) pathway is key for their alignment. The refinement of the tissue-wide expression of the atypical cadherins Ds and Ft result in their polarization and directional adhesiveness. Mechanistically, the axially oriented changes in histoblasts respond to the redesign of the epithelial field. We suggest that the role of Ds/Ft/Fj in long-range oriented cell alignment is a general function and that the regulation of the expression of its components will be crucial in other morphogenetic models or during tissue repair.

Comparison of the Viability and Yield of Adipose-Derived Stem Cells (ASCs) from Different Donor Areas.

BACKGROUND: Adipose tissue contains variable amounts of stem cells that have recently attracted increased interest due to their strong proliferative and differentiation capacity. However, significant heterogeneity exists in terms of stem cell yield and viability profile among individuals as well as different donor areas. MATERIALS AND METHODS: Between June 2016 and July 2016, forty (40) women underwent outpatient cosmetic liposuction procedures conferring a total of 53 lipoaspirates; inner thigh (n=13), outer thigh (n=9), abdomen (n=9), waist (n=16) and inner knee (n=6). Lipoaspirates were harvested using a tulip low-pressure syringe lipoaspiration system with a diameter of 3 mm. Centrifugation separated adipocytes from the stromal vascular fraction (SVF). Isolation of the adipose-derived stem cells (ASCs) was achieved through culture of the SVF. Viability of SVF cells and ASCs was evaluated with trypan blue dye under microscope and using flow cytometry with 7-AAD staining, respectively. Total cell count was estimated for both the SVF and ASCs. RESULTS: Outer thigh exhibited significantly higher SVF cell count compared to any other donor site (p<0.05). In addition, inner and outer thigh showed a significantly higher number of ASCs compared to abdominal, waist, and inner knee samples (p<0.05). Finally, viability of SVF cells (range, 94-95%) and ASCs (range, 93.12-96.14%) was excellent with no significant differences among donor areas. CONCLUSION: Tissue-harvesting area is a strong determinant of the quality of the fat grafts. Compared to abdomen, waist and inner knee, thighs seem favorable in terms of viability profile and yield of SVF cells and ASCs. Further randomized controlled trials incorporating a larger cohort of patients are warranted in order to verify our results.

Difference in Dachsous Levels between Migrating Cells Coordinates the Direction of Collective Cell Migration.

In contrast to extracellular chemotactic gradients, how cell-adhesion molecules contribute to directing cell migration remains more elusive. Here we studied the collective migration of Drosophila larval epidermal cells (LECs) along the anterior-posterior axis and propose a migrating cell group-autonomous mechanism in which an atypical cadherin Dachsous (Ds) plays a pivotal role. In each abdominal segment, the amount of Ds in each LEC varied along the axis of migration (Ds imbalance), which polarized Ds localization at cell boundaries. This Ds polarity was necessary for coordinating the migratory direction. Another atypical cadherin, Fat (Ft), and an unconventional myosin Dachs, both of which bind to Ds, also showed biased cell-boundary localizations, and both were required for the migration. Altogether, we propose that the Ds imbalance within the migrating tissue provides the directional cue and that this is decoded by Ds-Ft-mediated cell-cell contacts, which restricts lamellipodia formation to the posterior end of the cell.

Fetal and neonatal outcomes of preterm infants born before 32 weeks of gestation according to antenatal vs postnatal assessments of restricted growth.

BACKGROUND: Fetal growth restriction is defined using ultrasound parameters during pregnancy or as a low birthweight for gestational age after birth, but these definitions are not always concordant. OBJECTIVE: The purpose of this study was to investigate fetal and neonatal outcomes based on antenatal vs postnatal assessments of growth restriction. STUDY DESIGN: From the EPIPAGE 2 population-based prospective study of very preterm births in France in 2011, we included 2919 singleton nonanomalous infants 24-31 weeks gestational age. We constituted 4 groups based on whether the infant was suspected with fetal growth restriction during pregnancy and/or was small for gestational age with a birthweight <10th percentile of intrauterine norms by sex: 1) suspected with fetal growth restriction/small for gestational age 2) not suspected with fetal growth restriction/small for gestational age 3) suspected with fetal growth restriction/not small for gestational age and 4) not suspected with fetal growth restriction/not small for gestational age. We estimated relative risks of perinatal mortality and morbidity for these groups adjusting for maternal and neonatal characteristics. RESULTS: We found that 22.2% of infants were suspected with fetal growth restriction/small for gestational age, that 11.4% infants were not suspected with fetal growth restriction/small for gestational age, that 3.0% infants were suspected with fetal growth restriction/not small for gestational age, and that 63.4% infants were not suspected with fetal growth restriction/not small for gestational age. Compared with infants who were not suspected with fetal growth restriction/not small-for-gestational-age infants, small-for-gestational-age infants suspected and not suspected with fetal growth restriction had higher risks of stillbirth or termination of pregnancy (adjusted relative risk, 2.0 [95% confidence interval, 1.6-2.5] and adjusted relative risk, 2.8 [95% confidence interval, 2.2-3.4], respectively), in-hospital death (adjusted relative risk, 2.8 [95% confidence interval, 2.0-3.7] and adjusted relative risk, 2.0 [95% confidence interval, 1.5-2.8], respectively), and bronchopulmonary dysplasia (adjusted relative risk, 1.3 [95% confidence interval, 1.2-1.4] and adjusted relative risk, 1.3 [95% confidence interval, 1.1-1.4], respectively), but not severe brain lesions. Risks were not increased for infants suspected with fetal growth restriction but not small-for-gestational-age. CONCLUSION: Antenatal and postnatal assessments of fetal growth restriction were not concordant for 14% of very preterm infants. In these cases, birthweight appears to be the more relevant parameter for the identification of infants with higher risks of adverse short-term outcomes.

Clinical Validation of the INTERGROWTH-21st Standards of Fetal Abdominal Circumference for the Prediction of Small-for-Gestational-Age Neonates in Italy.

OBJECTIVES: To compare the accuracy of the INTERGROWTH-21st (IG-21) with the Italian Society of Ultrasound in Obstetrics and Gynecology (SIEOG) abdominal circumference (AC) standards in the detection of small-for-gestational-age (SGA) fetuses in a high-risk population. MATERIAL AND METHODS: Our study included all pregnant patients with an increased risk of placental insufficiency that were seen in two Italian university hospitals between 2014 and 2015. The accuracy of IG-21 and SIEOG AC standards in the detection of SGA neonates was analyzed by means of the area under the receiver operating characteristic curve (ROC-AUC) at 4 gestational age intervals (24-27, 28-31, 32-35, >35 weeks). RESULTS: We enrolled 428 patients (278 Italians). There was no significant difference between the ROC-AUC of AC according to IG-21 and SIEOG standards for all birthweight thresholds and gestational intervals that were considered. The diagnostic performance was similar in Italian and non-Italian patients. The accuracy was, however, limited, with values of ROC-AUC ranging between 0.80 and 0.89. CONCLUSIONS: The IG-21 and SIEOG AC standards are interchangeable for the diagnosis of SGA fetuses. The diagnostic accuracy is, however, limited. We provide figures that can be used to stratify the probability that an infant will be SGA in an obstetric population at increased risk of growth restriction.

Development of customized fetal growth charts in twins.

BACKGROUND: Twin gestations are at significantly higher risk of fetal growth restriction in comparison with singletons. Using fetal biometric charts customized for obstetrical and parental characteristics may facilitate an accurate assessment of fetal growth. OBJECTIVE: The objective of the study was to construct reference charts for the gestation of fetal biometric parameters stratified by chorionicity and customized for obstetrical and parental characteristics. STUDY DESIGN: Fetal biometric measurements obtained from serial ultrasound examinations in uncomplicated twin pregnancies delivering after 36 weeks of gestation were collected by 19 Italian fetal medicine units under the auspices of the Società Italiana di Ecografia Ostetrica e Ginecologica. The measurements acquired in each fetus at each examination included biparietal diameter, head circumference, abdominal circumference, and femur length. Multilevel linear regression models were used to adjust for the serial ultrasonographic measurements obtained and the clustering of each fetus in twin pregnancy. The impact of maternal and paternal characteristics (height, weight, ethnicity), parity, fetal sex, and mode of conception was also considered. Models for each parameter were stratified by fetal chorionicity and compared with our previously constructed growth curves for singletons. RESULTS: The data set included 1781 twin pregnancies (dichorionic, n = 1289; monochorionic diamniotic, n = 492) with 8923 ultrasonographic examinations with a median of 5 (range, 2-8) observations per pregnancy in dichorionic and 6 in (range, 2-11) monochorionic pregnancies. Growth curves of twin pregnancies differed from those of singletons, and differences were more marked in monochorionic twins and during the third trimester. A significant influence of parental characteristics was found. CONCLUSION: Curves of fetal biometric measurements in twins are influenced by parental characteristics. There is a reduction in the growth rate during the third trimester. The reference limits for gestation constructed in this study may provide a useful tool for a more accurate assessment of fetal growth in twin pregnancies.

Apoptotic forces in tissue morphogenesis.

It is now well established that apoptosis is induced in response to mechanical strain. Indeed, increasing compressive forces induces apoptosis in confined spheroids of tumour cells, whereas releasing stress reduces apoptosis in spheroids cultivated in free suspension (Cheng et al., 2009). Apoptosis can also be induced by applying a 100 to 250MPa pressure, as shown in different cultured cells (for review, see (Frey et al., 2008)). During epithelium development, the pressure caused by a fast-growing clone can trigger apoptosis at the vicinity of the clone, mediating mechanical cell competition (Levayer et al., 2016). While the effect of strain has long been known for its role in apoptosis induction, the reciprocal mechanism has only recently been highlighted. First demonstrated at the cellular level, the effect of an apoptotic cell on its direct neighbours has been analysed in different kinds of monolayer epithelium (Gu et al., 2011; Rosenblatt et al., 2001; Kuipers et al., 2014; Lubkov & Bar-Sagi, 2014). More recently, the concept of a broader impact of apoptotic cell behaviours on tissue mechanical strain has emerged from the characterisation of tissue remodelling during Drosophila development (Toyama et al., 2008; Monier et al., 2015). In the present review, we summarize our current knowledge on the mechanical impact of apoptosis during tissue remodelling.

Variability in the number of abdominal leucokinergic neurons in adult Drosophila melanogaster.

Developmental plasticity allows individuals with the same genotype to show different phenotypes in response to environmental changes. An example of this is how neuronal diversity is protected at the expense of neuronal number under sustained undernourishment during the development of the Drosophila optic lobe. In the development of the Drosophila central nervous system, neuroblasts go through two phases of neurogenesis separated by a period of mitotic quiescence. Although during embryonic development much evidence indicates that both cell number and the cell fates generated by each neuroblast are very precisely controlled in a cell autonomous manner, after quiescence extrinsic factors control the reactivation of neuroblast proliferation in a fashion that has not yet been elucidated. Moreover, there is very little information about whether environmental changes affect lineage progression during postembryonic neurogenesis. Using as a model system the pattern of abdominal leucokinergic neurons (ABLKs), we have analyzed how changes in a set of environmental factors affect the number of ABLKs generated during postembryonic neurogenesis. We describe the variability in ABLK number between individuals and between hemiganglia of the same individual and, by genetic analysis, we identify the bithorax-complex genes and the ecdysone hormone as critical factors in these differences. We also explore the possible adaptive roles involved in this process. J. Comp. Neurol. 525:639-660, 2017. © 2016 Wiley Periodicals, Inc.