Lethal presentation of mosaic tetrasomy 12p (Pallister-Killian) syndrome

A lethally malformed neonate with mosaic tetrasomy 12p is presented. This is the third reported case of mosaic tetrasomy 12p to have died in the neonatal period. These three babies have shown a consistent phenotype characterized by dysmorphic facies and large diaphragmatic hernia. Mosaic tetrasomy 12p is usually not detectable from lymphocyte investigation, indicating that chromosome studies from cultured fibroblasts should be undertaken in neonates with multiple malformations which include a diaphragmatic defect.     

Histoenzymology of the developing human basal ganglia

Summary Oxidative and hydrolytic enzyme activities are present in the anlage of the human basal ganglia as early as the second month of embryonic life, and acetylcholinesterase activity appears during the sixth month of pre-natal life.Clinical Research Fellow of the Medical Research Council. Presently in the Department of Neurology, Indiana University, Medical School.     

The role of metal ions in the conformation of the four-way DNA junction.

Metal ions fold DNA junctions into a compact conformation that confers protection of all thymine bases to modification by osmium tetroxide. In the absence of the cation the arms of the junction are fully extended in an approximately square-planar configuration. Group IIa cations are effective in achieving a folded conformation of the junction at 80-100 microM, and there is an excellent agreement between the ionic concentrations that fold the junctions as deduced from gel electrophoretic experiments, and those that prevent osmium tetroxide reaction at the junction. Hexamminecobalt(III) achieves full folding at 2 microM, while spermine and spermidine are effective at 25 microM. Some transition metal ions such as Ni(II) may replace the group IIA cations. Monovalent ions of group IA are only partially effective in folding the junctions. Very much higher concentrations are necessary, gel electrophoretic mobilities suggest that a less symmetrical conformation is adopted and thymine bases at the junction remain reactive to osmium tetroxide. Charge-charge interactions at the centre of the junction are structurally extremely important. Substitution of junction phosphate groups by uncharged methyl phosphonates severely perturbs the structure of the junction. If just two phosphates are substituted, diametrically facing across the junction, the structure always folds in order to place the electrically neutral phosphate on the exchanging strands. We suggest that folding of the junction into the stacked X-structure generates electronegative clefts that can selectively bind metal ions, depending on the chemistry, size and charge of the ion. Moreover, occupation of these cavities is essential for junction folding, in order to reduce electrostatic repulsion.(ABSTRACT TRUNCATED AT 250 WORDS)     

Localization of sequences regulating ancestral and acquired sites of esterase6 activity in Drosophila melanogaster

We have broadly defined the DNA regions regulating esterase6 activity in several life stages and tissue types of D. melanogaster using P- element-mediated transformation of constructs that contain the esterase6 coding region and deletions or substitutions in 5' or 3' flanking DNA. Hemolymph is a conserved ancestral site of EST6 activity in Drosophila and the primary sequences regulating its activity lie between -171 and -25 bp relative to the translation initiation site: deletion of these sequences decrease activity approximately 20-fold. Hemolymph activity is also modulated by four other DNA regions, three of which lie 5' and one of which lies 3' of the coding region. Of these, two have positive and two have negative effects, each of approximately twofold. Esterase6 activity is present also in two male reproductive tract tissues; the ejaculatory bulb, which is another ancestral activity site, and the ejaculatory duct, which is a recently acquired site within the melanogaster species subgroup. Activities in these tissues are at least in part independently regulated: activity in the ejaculatory bulb is conferred by sequences between -273 and -172 bp (threefold decrease when deleted), while activity in the ejaculatory duct is conferred by more distal sequences between -844 and -614 bp (fourfold decrease when deleted). The reproductive tract activity is further modulated by two additional DNA regions, one in 5' DNA (-613 to -284 bp; threefold decrease when deleted) and the other in 3' DNA (+1860 to +2731 bp; threefold decrease when deleted) that probably overlaps the adjacent esteraseP gene. Collating these data with previous studies suggests that expression of EST6 in the ancestral sites is mainly regulated by conserved proximal sequences while more variable distal sequences regulate expression in the acquired ejaculatory duct site.      

Structures of bulged three-way DNA junctions.

We have studied a series of three-way DNA junctions containing unpaired bases on one strand at the branch-point of the junctions. The global conformation of the arms of the junctions has been analysed by means of polyacrylamide gel electrophoresis, as a function of conditions. We find that in the absence of added metal ions, all the results for all the junctions can be accounted for by extended structures, with the largest angle being that between the arms defined by the strand containing the extra bases. Upon addition of magnesium (II) or hexamine cobalt (III) ions, the electrophoretic patterns change markedly, indicative of ion-dependent folding transitions for some of the junctions. For the junction lacking the unpaired bases, the three inter-arm angles appear to be quite similar, suggesting an extended structure. However, the addition of unpaired bases permits the three-way junction to adopt a significantly different structure, in which one angle becomes smaller than the other two. These species also exhibit marked protection against osmium addition to thymine bases at the point of strand exchange. These results are consistent with a model in which two of the helical arms undergo coaxial stacking in the presence of magnesium ions, with the third arm defining an angle that depends upon the number of unpaired bases.     

The iap genes: unique arbitrators of cell death

The iap family of anti-apoptotic genes, originally discovered in viruses, has grown considerably in the past two years with the addition of a number of evolutionary conserved cellular homologues. Although the mechanism(s) by which these novel proteins block cell death is still unknown, intriguing clues to their function have been revealed by the discovery of interactions between some of the IAP homologues and cellular proteins involved in carrying out apoptotic signalling. Here, Rollie Clem and Colin Duckett discuss how the various IAP proteins may function in regulating apoptosis.     

Nucleotide variation at the hypervariable esterase 6 isozyme locus of Drosophila simulans

Esterase 6 (Est-6/EST6) is polymorphic in both Drosophila melanogaster and D. simulans for two common allozyme forms, as well as for several other less common variants. Parallel latitudinal clines in the frequencies of the common EST6-F and EST6-S allozymes in these species have previously been interpreted in terms of a shared amino acid polymorphism that distinguishes the two variants and is subject to selection. Here we compare the sequences of four D. simulans Est-6 isolates and show that overall estimates of nucleotide heterozygosity in both coding and 5' flanking regions are more than threefold higher than those obtained previously for this gene in D. melanogaster. Nevertheless, the ratio of replacement to exon silent-site polymorphism in D. simulans is less than the ratio of replacement to silent divergence between D. simulans and D. melanogaster, which could be the result of increased efficiency of selection against replacement polymorphisms in D. simulans or to divergent selection between the two species. We also find that the amino acid polymorphisms separating EST6- F and EST6-S in D. simulans are not the same as those that separate these allozymes in D. melanogaster, implying that the shared clines do not reflect shared molecular targets for selection. All comparisons within and between the two species reveal a remarkable paucity of variation in a stretch of nearly 400 bp immediately 5' of the gene, indicative of strong selective constraint to retain essential aspects of Est-6 promoter function.      

Ultrastructural studies of mutant spermatozoids in ferns. I. The mature nonmotile spermatozoid of mutation 230X in Ceratopteris thalictroides(L.)Brongn

Electron microscopy reveals that nonmotility in the spermatozoids of mutant 230X of the fern Ceratopteris thalictroides results from highly aberrant flagella. With respect to its mitochondrial complement, amyloplasts, condensed chromatin within the nucleus and the multilayered structure (MLS), the mutation is almost indistinguishable from the wild-type spermatozoids. In contrast to flagellar mutations in other organisms (man, mouse, Drosophila, Chlamydomonas), which principally affect the microtubules of the axoneme, the basal body cartwheel is lacking in 230X. In its absence, compound microtubules with shared walls are still present, but in highly disorganized arrays. Since the amount of polymerized tubulin in the spermatozoids of 230X is approximately the same as in the wild type, the mutation does not seem to affect microtubule synthesis or assembly. Centriolar cartwheels appear to be essential templates for the alignment of triplet and doublet tubules in regular radial arrays. The MLS in 230X is almost normal, whereas the flagella are aberrant, indicating that there are two distinct functional classes of microtubules in archegoniate spermatozoids. In contrast to the helix of 3½ gyres found in the wild type, nuclear morphology in 230X exhibits profound distortions ranging from deep channels and holes to supernumerary attenuated arms. Parts of nuclei associated with the MLS are almost normal, but malformations are in variably associated with the presence of microtubules of the aberrant flagella that are in close proximity t o the nuclear surface. The shapes of the teratologies are directly related to the number and configuration of the adjacent perinuclear tubules. From these findings, it is argued that microtubules have a crucial role in nuclear shaping in archegoniates; and that the precise form of the nucleus is closely related to the geometry and development of the MLS. On the other hand, it is difficult to envisage how microtubules growing in the chaotic arrays found in 230X could themselves generate shaping forces, More likely, the actual force-generating system, situated in or near the nuclear envelope, has become misaligned and severely restricted by the perinuclear arrays of flagellar tubules, which function as cytoskeletal elements additional to those of the normal MLS. Archegoniate plants are particularly advantageous for the detection of basal body mutants, since centrioles are absent from the mitotic apparatus. Cytological and hybridization studies of 230X affirm the nuclear basis of the mutation, and provide no support for the possible genetic autonomy of centrioles.