Search PubMed⌕ Search

Biomedical subjects

T D Allen

Publications and source records attributed to T D Allen.

At least 19 recordsLinked to original sources
PubMed1992

Unilateral post-obstructive diuresis in the neonate.

A total of 3 neonates exhibited severe post-obstructive diuresis after relief of unilateral ureteral obstruction. Of the neonates 2 had normal kidneys contralaterally while 1 had a contralateral kidney that was dysplastic. Urinary output exceeded oral intake initially in all 3 patients necessitating intravenous supplementation for up to 10 days. Stabilization resulted from an increase in oral intake rather than a decrease in diuresis. Unilateral post-obstructive diuresis is extremely uncommon but it may occur in the neonate because of the unique features of the renal physiology encountered in this age patient.

Diuresis↗
PubMed1992

Exstrophy of the bladder: primary closure after iliac osteotomies without external or internal fixation.

A total of 6 consecutive infants with exstrophy of the bladder underwent iliac osteotomy in association with primary closure of the bladder without internal or external fixation of the bony pelvis. Hospitalization time was short and there were no resulting problems with healing, bony deformities or subsequent ambulation. Fixation of the bony pelvis after iliac osteotomy does not appear to be necessary in nonambulatory patients undergoing primary closure for bladder exstrophy.

Bladder Exstrophy↗
PubMed1992

High resolution scanning electron microscopy of the nuclear envelope: demonstration of a new, regular, fibrous lattice attached to the baskets of the nucleoplasmic face of the nuclear pores.

The nuclear envelope (NE) of amphibian oocytes can be readily isolated in relatively structurally intact and pure form and has been used extensively for structural studies. Using high resolution scanning electron microscopy (HRSEM), both surfaces of the NE can be visualized in detail. Here, we demonstrate the use of HRSEM to obtain high resolution information of NE structure, confirming previous data and providing some new information. NEs, manually isolated from Triturus cristatus oocytes, have been mounted on conductive silicon chips, fixed, critical point dried and coated with a thin, continuous film of chromium or tantalum and viewed at relatively high accelerating voltage in a field emission scanning electron microscope with the sample within the objective lens. Both nucleoplasmic and cytoplasmic surfaces of the nuclear pore complexes (NPC) have been visualized, revealing the cytoplasmic coaxial ring, associated particles, central plug/transporter and spokes. The nucleoplasmic face is dominated by the previously described basketlike structure attached to the nucleoplasmic coaxial ring. In Triturus, a novel, highly regular flat sheet of fibers, termed the NE lattice (NEL) has been observed attached to the distal ring of the NPC basket. The NEL appears to be distinct from the nuclear lamina. Evidence for the NEL is also presented in thin TEM sections from Triturus oocytes and GVs and in spread NEs from Xenopus. A model is presented for NEL structure and its interaction with the NPCs is discussed.

Amphibians↗
PubMed1992

Transforming growth factor beta 1 promotes the differentiation of endothelial cells into smooth muscle-like cells in vitro.

Alpha-smooth muscle actin is considered a reliable marker for distinguishing between arterial smooth muscle and endothelial cells. Several authors have reported heterogeneity in the expression of this actin isoform in atherosclerotic lesions. Such heterogeneity appears to result from the presence of different smooth muscle cell phenotypes (contractile and synthetic) in these lesions. In the present study, we show that bovine aortic endothelial cells, which are characterised by the presence of Factor VIII-related antigen (FVIII) and by the absence of alpha-smooth muscle actin (alpha-SM actin) may be induced to express the latter when exposed to TGF-beta 1. FVIII was detected by immunofluorescence, alpha-SM actin was detected by immunofluorescence and immunoblotting. The number of cells expressing alpha-SM actin increased with time of incubation with TGF-beta 1, and this increase occurred concomitantly with a decrease in the expression of FVIII. Double immunofluorescence demonstrated the presence of cells that expressed both FVIII and alpha-SM actin after 5 days of incubation with TGF-beta 1. With longer incubation times (10-20 days) the loss of FVIII expression was complete and over 90% of the cells expressed alpha-SM actin. Ultrastructurally, cells in control cultures showed the typical features of endothelial cells. In the TGF-beta 1-treated cultures, cells which appeared indistinguishable from contractile and synthetic smooth muscle cells were observed. Withdrawal of TGF-beta 1 after 10 days incubation resulted in the re-appearance of polygonal cells which were FVIII-positive and alpha-SM actin-negative.(ABSTRACT TRUNCATED AT 250 WORDS)

Actins↗
PubMed1991

ATP dependent histone phosphorylation and nucleosome assembly in a human cell free extract.

Physiologically spaced nucleosome formation in HeLa cell extracts is ATP dependent. ATP hydrolysis is required for chromatin assembly on both linear and covalently closed circular DNA. The link between the phosphorylation state of histones and nucleosome formation has been examined and we demonstrate that in the absence of histone phosphorylation no stable and regularly spaced nucleosomes are formed. Phosphorylated H3 stabilizes the nucleosome core; while phosphorylation of histone H2a is necessary to increase the linker length between nucleosomes from 0 to approximately 45 bp. Histone H1 alone, whether phosphorylated or unphosphorylated, does not increase the nucleosome repeat length in the absence of core histone phosphorylation. Phosphorylations of H1 and H3 correlate with condensation of chromatin. Maximum ATP hydrolysis which is necessary to increase the periodicity of nucleosomes from approximately 150 to approximately 185 bp, not only inhibits H1 and H3 phosphorylation but facilitates their dephosphorylation.

Adenosine Triphosphate↗
PubMed1991

Identification of amino acids in lac repressor protein cross-linked to operator DNA specifically substituted with bromodeoxyuridine.

Amino acids in lac repressor protein which form cross-links to lac operator DNA specifically substituted with bromodeoxyuridine (BrdU) have been identified. Five sites of cross-linking in BrdU-substituted operator DNA were found at positions +3, +4, +14, +18, and +19 relative to the initiation site for transcription (Wick, K.L., and Matthews, K.S. (1991) J. Biol. Chem. 266, 6106-6112). Irradiation of complexes of repressor and each of these five singly substituted operator DNAs was executed under large scale conditions to generate sufficient complex for proteolysis, separation of the peptide-DNA, and peptide sequencing. The DNAs substituted with BrdU for thymidine at positions +3, +18, and +19 yielded cross-links to the peptide spanning residues 23-33, with the cross-link identified at His-29. Substitution at position +14 resulted in a cross-link to Tyr-17 within the peptide containing amino acids 13-22. These results are consistent with the structure determined by NMR and molecular dynamics calculations of the NH2-terminal headpiece-symmetric operator complex (Lamerichs, R.M.J.N., Boelens, R., van der Marel, G.A., van Boom, J.H., Kaptein, R., Buck, F., Fera, B., and Rüterjans, H. (1989) Biochemistry 28, 2895-2991; de Vlieg, J., Berendsen, H.J.C., and van Gunsteren, W.F. (1989) Proteins 6, 104-127). This structure indicates proximity of His-29 in the major groove to thymidines at positions +3 and +4. Since base pairs at positions +18 and +19 occupy symmetrical positions to +3 and +4 in the promoter distal region of the operator, it would be anticipated that cross-links similar to the +3 and +4 positions would form at these sites; this prediction is not borne out by the behavior at +4/+18, as no peptide could be identified cross-linked to DNA substituted at +4. Molecular dynamics simulations and the NMR data indicate that Tyr-17 interacts with the thymine at position +8, which is symmetrically related to position +14. Although BrdU-associated strand scission at +8 is protected, this site does not cross-link with bound lac repressor; inversely, DNA substituted with BrdU at +14 cross-links to repressor, but is not protected from strand scission by the presence of the protein. These differences at symmetrically related nucleotide positions (+4 versus +18, +8 versus +14) reflect the inherent asymmetry in the interaction. The identification of amino acids in proximity to specifically substituted sites confirms that positions of several amino acids in the intact protein-operator complex correspond to those in the structure of the NH2-terminal headpiece-operator DNA complex.

Amino Acid Sequence↗
PubMed1991

Resolution of vesicoureteral reflux in completely duplicated systems: fact or fiction?

A total of 60 patients (71 renal units) with grade 2/5 vesicoureteral reflux into the lower pole moiety of a completely duplicated system was managed by medical surveillance and is compared to an identically managed age, race and sex matched control population with a similar degree of reflux into a single collecting system. During a median 2-year observation period reflux ceased spontaneously in 10% of the patients with duplication compared to 35% of the control population (p less than 0.01). Comparisons between the 2 study groups failed to reveal a difference in the incidence of break-through urinary tract infections, advancing degrees of reflux and/or the development or progression of renal scarring (p greater than 0.5). Despite the fact that the resolution rate in duplex systems is significantly lower than that of a single system, it is apparent that cessation of grade 2/5 reflux into a duplicated ureter will occur and that a trial of medical management is an appropriate initial method of therapy.

Actuarial Analysis↗
PubMed1991

Cloacal anomalies and other urorectal septal defects in female patients: a spectrum of anatomical abnormalities.

The anatomy and management of 16 female patients with urorectal septal defects have been reviewed. The diagnosis was often confused by the anomalous appearance of the external genitalia, and the internal arrangements of the urinary tract, genital tract and lower intestinal tract were frequently bizarre and unpredictable. Because of the potential of these patients for secondary infection and sepsis, a prompt and thorough anatomical evaluation in such cases is essential. Initial treatment should be directed toward decompression of the involved organ systems and definitive reconstruction should be deferred until the child is older, at which time the emphasis should be upon a simultaneous multisystem repair performed, whenever possible, in 1 stage.

Abnormalities, Multiple↗
PubMed1991

Ultrastructural and morphometric alterations in bone marrow stromal tissue after 7 Gy irradiation.

To evaluate the response of marrow stroma to 7 Gy irradiation, femoral bone marrow was fixed by vascular perfusion (so as to avoid the artificial destruction of sinus endothelia), and was examined using light and electron microscopy with morphometric methods. The radiation caused a marked decrease in hematopoietic cell number (NHC) within 3 days post-irradiation, followed by total recovery of hematopoiesis, which occurred gradually over 28 days. An increased number of fat cells was seen by 7 days. During the whole course of hypoplasia and recovery, the continuity of sinus wall, three-dimensional reticular mesh work in hematopoietic parenchyma, gap junctions (GJ) between stromal cells, the adventitial cell cover of sinus wall (ACC), and the stromal cell numbers of reticular cells (RC), sinus endothelia (SE), and macrophages (MP) were maintained. The cellularity of stromal components of RC, SE, and MP seemed passively increased in contrast to a reduction in numbers of NHC. A similar tendency was observed (1) between NHC and ACC and (2) between GJ and the cellularity of fat cells, which had a statistical significant correlation (p less than 0.05; t-test). The mechanism of radio resistance in bone marrow stroma and the possible functional adaptation and cellular coordination after irradiation are discussed.

Adipose Tissue↗
PubMed1991

Cellular interactions in erythroblastic islands in long-term bone marrow cultures, as studied by time-lapse video.

Long-term bone marrow cultures (LTBMC) are readily converted from the usual granulopoietic to erythropoietic production by the addition of anemic mouse serum (AMS). The "statics" of proliferation and maturation, previously shown by ultrastructural methods to closely mirror the in vivo situation, were studied dynamically using a time-lapse video system. Several cell pedigrees were followed, but the most complete series showed three successive divisions and subsequent enucleations in the progeny of three synchronously mitotic cells observed in the culture; this is indicative of a five division sequence in the erythron. As in erythroblastic islets observed in marrow in vivo, the striking synchrony of maturation was maintained in vitro. Furthermore, when some of the erythroid progeny became displaced to other macrophages, the synchrony, which was maintained by the original erythroid group on the original erythroblastic islet macrophage, was lost. Time-lapse video, which is inexpensive to run and can be maintained in continuous recording for many weeks, is an ideal technique for recording both erythroid cell pedigrees, and the initial events leading to the formation of an erythroblastic islet in vitro after stimulation with AMS.

Animals↗
PubMed1990

Stromal cells in haemopoiesis.

Stromal cells of the bone marrow can provide the growth-promoting and differentiation-inducing molecules which are necessary for haemopoiesis. While the nature of these stimuli is largely unknown, the development of haemopoietic cells in association with stromal cells requires intimate cell contact. Molecules of the extracellular matrix, such as heparan sulphate, are able to bind growth factors and in this way the stromal cells may form microenvironmental niches which preferentially promote development of multipotent and committed cells along discrete lineages. Cells from some patients with acute and chronic myeloid and lymphoid leukaemias are defective in their ability to interact with stromal cells and consequently cannot survive in stromal cell-mediated long-term marrow cultures. We have exploited this phenomenon to obtain normal haemopoietic cells from patients with leukaemia, and to use these cells for successful autografting in patients with acute and chronic myeloid leukaemias.

Animals↗
PubMed1990

Pericytes derived from the retinal microvasculature undergo calcification in vitro.

Pericytes isolated from the bovine retinal microvasculature retain characteristic features of their in vivo counterparts, such as the presence of glycogen deposits, long filamentous processes, prominent microfilament bundles and the ability to display two distinct and reversible phenotypes. Time-lapse video-microscopy demonstrated that pericytes tend to overlap and aggregate, even in sparse cultures. After reaching confluence, they form multilayered areas that retract away from each other, resulting in the formation of multicellular nodules. These nodules increase in size and cellularity by going through repeated 5- to 6-h cycles of anchoring, spreading, cell proliferation and retraction. Alkaline phosphatase was not detected in pericytes at subconfluent or confluent densities, but this enzyme was expressed in areas of high cell density, such as multilayers and nodules. Pericytes synthesise and deposit an extracellular matrix at all stages of their in vitro development, including nodule formation. The matrix within the nodules contains cross-striated collagen fibres and matrix vesicles. Needle-like crystals of hydroxyapatite appear to be deposited within the matrix, thus leading to massive calcification of the nodule. Calcification, as assessed by electron microscopy, histochemical staining and X-ray microprobe analysis, occurred on plastic and collagen substrate in the absence of disodium-beta-glycerophosphate. The addition of this compound at 5 or 10 mM or the use of a collagen substratum (rather than plastic), brought forward the process of nodule formation and calcification by 3-6 days. Our results suggest that retinal pericytes may differentiate in vitro along the osteogenic pathway.

Animals↗