Instrumental stability requirements for exoplanet detection with a nulling interferometer: variability noise as a central issue

We revisit the nulling interferometer performances that are needed for direct detection and the spectroscopic analysis of exoplanets, e.g., with the DARWIN [European Space Agency-SCI 12 (2000)] or TPF-I [JPL Publ. 05-5, (2005)] missions. Two types of requirement are found, one concerning the mean value of the instrumental nulling function (nl(lambda)) and another regarding its stability. The stress is usually put on the former. It is stringent at short wavelengths but somewhat relaxed at longer wavelengths. The latter, which we call the variability noise condition, does not usually receive enough attention. It is required regardless of telescope size and stellar distance. The results from three nulling experiments performed in laboratories around the world are reported and compared with the requirements. All three exhibit 1/f noise that is incompatible with the performances required by the mission. As pointed out by Lay [Appl. Opt. 43, 6100-6123 (2004)], this stability problem is not fully solved by modulation techniques. Adequate solutions must be found that are likely to include servo systems using the stellar signal itself as a reference and internal metrology with high stability.

Use of single-mode waveguides to correct the optical defects of a nulling interferometer

In the area of long-baseline nulling interferometry, high rejection ratios are needed to cancel out the light of a bright central source and look for nearby faint structures or companions. These rejection requirements directly translate into drastic optical constraints. We discuss the possibility of using single-mode waveguides for such applications. Conversely to simple pinholes, single-mode waveguides efficiently correct wave-front defects of both high- and low-order spatial frequencies, ensure a perfect matching of the amplitude profiles coming from the various beams, and can be used with almost optimum coupling efficiency over a broad optical bandpass (typically an octave). They then appear to greatly enhance the feasibility of high-dynamic interferometric coronagraphs.

FUT4 and FUT9 genes are expressed early in human embryogenesis

The Le(x) oligosaccharide is expressed in organ buds progressing in mesenchyma, during human embryogenesis. Myeloid-like alpha3-fucosyltransferases are good candidates to synthesize this oligosaccharide. We investigated by Northern analysis all the alpha3-fucosyltransferase gene transcripts and only FUT4 and FUT9 were detected. The enzymes encoded by the FUT4 and FUT9 genes are the first alpha3-fucosyltransferases strongly expressed during the first two months of embryogenesis. The Northern profile of expression of the embryo FUT4 transcripts is similar in size and sequence to the known FUT4 transcripts of 6 kb, 3 kb, and 2.3 kb, but a new FUT9 transcript of 2501 bp, different from the known mouse (2170 bp) and human (3019 bp) transcripts was cloned. FUT3, FUT5, FUT6, and FUT7 were not detected by Northern blot. The FUT3 and FUT6 transcripts start to appear at this stage, but are only detected by reverse transcriptase-PCR analysis. The expression of FUT5 is weaker than FUT3 and FUT6 and the RT-PCR signal is faint and irregular. FUT7 is not detected at all. Using mRNA from 40- to 65-day-old embryos, we have prepared different hexamer and oligo-dT cDNA libraries and cloned, by rapid amplification cDNA ends-PCR, FUT4 and FUT9 alpha3-fucosyltransferase transcripts. The tissue expression of the embryonic FUT9 transcript is closer to that observed for the mouse (brain), than to the known human (stomach) transcripts. The acceptor specificity and the kinetics of the alpha3-fucosyltransferase encoded by this FUT9 transcript are similar to the FUT4 enzyme, except for the utilization of the lac-di-NAc acceptor which is not efficiently transformed by the FUT9 enzyme. Like FUT4, this embryonic FUT9 is N-ethylmaleimide and heat resistant and the corresponding gene was confirmed to be localized in the chromosome band 6q16. Finally, this FUT9 transcript has a single expressed exon as has been observed for most of the other vertebrate alpha2- and alpha3-fucosyltransferases.

Expression of fucosyltransferases in skin, conjunctiva, and cornea during human development

During human development, type-1-precursor, sialyl-Le a, and Le x antigens were present in the periderm of skin and eye at week 6. The Le x antigen disappeared from cornea at 10 weeks and then from skin at 20 weeks. H-type-1, Le a, Le b, sialyl-Le a, H-type-2, sialyl-Le x, and Le y were found in cornea, conjunctiva, and periderm between 10 and 20 weeks. They disappear from the skin (at week 20) and progressively reappear in skin derivatives, especially in the epithelium of sweat glands. The secretory part of the sweat gland is type-1-precursor and H-type-1 positive while its excretory part is Le a, Le b, sialyl-Le a, and Le y positive. On the eye surface the disappearance of Le x at 10 weeks and of the H-type-1, sialyl-Le x, and Le y at week 35 starts in the central cornea in front of the lens. The corneal epithelium and the conjunctiva have similar antigens to those of excretory and secretory parts of the sweat gland, respectively. Invaginations and folding of the epidermis might preserve the embryonic staining. We propose that fucosylation patterns are associated with the embryonic origin and differentiation stage of tissue. The early and transient presence of Le x is associated with FUT4 or FUT9 activities, while the late appearance of Lewis antigens is related to other alpha3-fucosyltransferases.

[Tissue expression of a gene potentially implicated in some diseases with retinal and renal involvement]

We have produced a monoclonal antibody (HA34) that specifically reveals the pigmented epithelium in the eye and the proximal convoluted tubules of the kidney, whatever the developmental stage. The results obtained with the kidney of other mammals suggest that the antigen is human specific. Its molecular weight is approximately 200 kDa. The epitope recognized by HA34 is always present on cell lines grown in vitro. This allowed us to use somatic cell interspecific hybrids to localize the gene implicated in the cytogenetic band 11q13, between microsatellites D11S1777 (AFMa046wa9) and D11S913 (AFM164zf12) in a 9 cM space. This region is involved in forms of retinitis pigmentosa, some of which can also include kidney abnormalities. We propose that this gene is possibly implicated in some of these diseases.

Complications of diagnostic ultrasound-guided percutaneous umbilical blood sampling: analysis of a series of 341 cases and review of the literature

OBJECTIVE

To study the complications of percutaneous umbilical blood sampling (PUBS) conducted for purely diagnostic purposes, in a retrospective study of 341 personal cases and an analysis of 4922 cases from literature.

SUBJECT

Analysis of the sampling procedure and complications seen in 341 punctures, including 12 failures.

INTERVENTIONS

Freehand echo-guided percutaneous umbilical blood sampling. PARAMETERS STUDIED: Conditions in which the blood samples were taken (gestational age, indications, placental location, technique--including number of punctures, duration); total number of fetal deaths and number of fetal deaths related to the procedure; other complications (bradycardia, hematoma of the umbilical cord, hemorrhage, premature births).

RESULTS

20 fetal deaths (FDs) were recorded in 341 cases (5.87%) (figures for the literature: 189/4922 = 3.84%); 3 FDs appeared to be directly related to the procedure (0.88) (figures for the literature: 48/4922 = 0.98%). There were 32 cases of bradycardia (9.38%); this complication was seen more frequently after repeated and prolonged punctures. Hematomas of the cord (1.47%) were seen when punctures were attempted in a free loop of the cord. There was a marked increase in the number of complications (8.96% FDs and 20.73% of bradycardias) when the procedure lasted more than 10 min and/or when more than 3 punctures were attempted (33.33% FDs). These two occurrences are closely related to the gestational age at which the PUBS was conducted, the placental location, the experience of the operators and the condition for which the sample was being taken. Pathological pregnancies (fetal malformation, disease or hypotrophy of the fetus, diseases of the amniotic fluid) had a mortality rate of 11.24% (19/169), whereas fetuses that were presumed to be healthy had a lower risk of 0.58% (1/172).

CONCLUSIONS

The overall mortality (including all fetal and neonatal deaths) appears to be around 5.0% (between 3.84 and 5.87%), but the mortality rate directly related to the procedure seems to be around 1% (between 0.88 and 0.98%). It seems that the fetal mortality rate is closely related to: (a) The state of the fetus and thus to the indication of the procedure. The higher overall mortality rate observed is related to the natural history of the conditions for which the procedure was conducted and the time taken to conduct the procedure and the number of punctures. This depends on the experience of the teams, on the observation of the rule that the attempt should not be prolonged beyond 10 min and no more than 2 punctures should be attempted in any one session.

Alpha-3-fucosyltransferases and their glycoconjugate antigen products in the developing human kidney

BACKGROUND

Three patterns of alpha-3-fucosyltransferase activity have been described in human adult tissues with different acceptor specificity: myeloid, plasma and Lewis. Five- to ten-week embryos express the myeloid enzyme in all tissues tested, then this enzyme is replaced by plasma or Lewis enzymes, with the exception of leukocytes that continue to express the myeloid form of the enzyme in the adult. These enzymes have not been studied as yet in the developing human kidney.

EXPERIMENTAL DESIGN

The three different alpha-3-fucosyltransferases were studied in homogenates of mesonephros and metanephros with synthetic oligosaccharide acceptors. The oligosaccharide precursors and products of these enzymes (precursor, H, Le(a), sialyl-Le(a) and Le(b) for type 1 and precursor, H, Le(x), sialyl-Le(x) and Le(y) for type 2) were localized by immunofluorescence with specific antibodies.

RESULTS

Only the myeloid alpha-3-fucosyltransferase is detected at 5 weeks in mesonephros and it disappears at 8 weeks. In metanephros, the myeloid enzyme alone is detected between weeks 6 and 8. The plasma enzyme then appears and only at the last trimester of gestation does the Lewis enzyme appear. Three histologic patterns that are concordant with the expression of the alpha-3-fucosyltransferases are observed: I. Inducer, S-shaped body, Bellini and calyce express Le(x) at an early stage when, only the myeloid alpha-3-fucosyltransferase is detected; II. Later, the proximal tubules and descending limbs of Henle's loop express Le(x) (week 9) and sialyl-Le(x) (week 16) when the plasma alpha-3-fucosyltransferase appears; III. Calyceal and collecting systems always express Le(x) and after week 12 Le(a) and Le(b) appear, in accordance with the late appearance of Lewis alpha-3/4-fucosyltransferase.

CONCLUSIONS

The sequential appearance of enzymes and their products suggests that during renal organogenesis the myeloid alpha-3-fucosyltransferase is progressively replaced by the plasma enzyme in the proximal tubules and later by the Lewis enzyme in Bellini's ducts and calyce.

Prenatal diagnosis of cystic fibrosis: ultrasonography of the gallbladder at 17-19 weeks of gestation

We have investigated the ultrasonographic signs that can help in the prenatal diagnosis of cystic fibrosis in 197 risk fetuses and compared them with 353 control fetuses. In 60 fetuses with a 1:4 risk for the disease, the gallbladder was also examined. All ultrasonograms were performed just before amniocentesis at 17-19 weeks of gestation. A previously described intra-abdominal hyperechogenic mass was found in 73% of the 48 affected fetuses, but 32 of the 149 unaffected fetuses also had this feature, giving a specificity of 77% and a sensitivity of 78%. When we investigated the gallbladder, we found 9 of the 12 affected fetuses to be without evidence of a gallbladder during the sonographic examination (none of the healthy or control fetuses had such a feature), giving a positive predictive value of 100%, a specificity of 100% and a sensitivity of 75%. The combined presence of an abnormal gallbladder and a hyperechogenic intra-abdominal mass yields the same positive predictive value and specificity, but does not improve the accuracy. Ultrasonography appears to be a good additional diagnostic tool for the prenatal diagnosis of cystic fibrosis, especially when the enzyme activities disagree. Furthermore, these results lead us to think that such a finding during routine ultrasonographic examination at 17-29 weeks could be a means of screening for cystic fibrosis. The absence of the gallbladder during the sonographic examination of fetuses at risk for cystic fibrosis at 17-19 weeks of gestation can help in the prenatal detection of the disease.

Five specificity patterns of (1----3)-alpha-L-fucosyltransferase activity defined by use of synthetic oligosaccharide acceptors. Differential expression of the enzymes during human embryonic development and in adult tissues

The use of synthetic trisaccharides as acceptors led to the definition of five main (1----3)-alpha-L-fucosyltransferase activity patterns in human adult tissues: (I). Myeliod cells, granulocytes, monocytes, and lymphoblasts, transfer an alpha-L-fucopyranosyl group to O-3 of a 2-acetamido-2-deoxy-D-glucosyl residue of H blood-group Type 2 oligosaccharide [alpha-L-Fucp-(1----2)-beta-D-Galp-(1----4)-beta-D-GlcpNAc----R] with Mn2+ as activator. (II) Brain has the same acceptor specificity pattern as myeloid cells, but can also use Co2+ as activator. (III) Plasma and liver transfer an alpha-L-furopyranosyl group to H blood-group Type 2 and to sialyl-N-acetyllactosamine [alpha-NeuAc-(2----3)-beta-D-Galp-(1----4)-beta-D-GlcpNAc----R]. (IV) Intestine, gall bladder, kidney, and milk have the same activity as (III), but also transfer an alpha-L-fucopyranosyl group to O-4 of a 2-acetamido-2-deoxy-D-glucose residue of H blood-group Type 1 [alpha-L-Fucp-(1----2)-beta-D-Galp-(1----3)-beta-D-GlcpNAc----R] and sialyl Type 1 [alpha-NeuAc-(1----3)-beta-D-Galp-(1----3)-beta-D-GlcpNAc----R]. (V) Stomach mucosa is not able to use sialyl-N-acetyllactosamine, but can transfer an alpha-L-fucopyranosyl group to the other Type 1 and Type 2 acceptors. Unlike in adult tissue, a single myeloid-like pattern of (1----3)-alpha-L-fucosyltransferase activity was found at early stages of development in all tissues tested. This embryonic enzyme is later progressively replaced by enzymes or mixtures of enzymes having the corresponding adult patterns of enzyme expression. All lymphoblastoid cell lines and half of the tumor epithelial cell lines tested expressed the myeloid-like pattern of enzyme found in normal embryonic tissues. The remaining tumor epithelial cell lines expressed different forms of (1----3/4)-alpha-L-fucosyltransferase acceptor specificity patterns.