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Biomedical subjects

A Poznanski

Publications and source records attributed to A Poznanski.

13 recordsLinked to original sources
PubMed1997

Epithelial cell wedging and neural trough formation are induced planarly in Xenopus, without persistent vertical interactions with mesoderm.

In this study we investigate the induction of the cell behaviors underlying neurulation in the frog, Xenopus laevis. Although planar signals from the organizer can induce convergent extension movements of the posterior neural tissue in explants, the remaining morphogenic processes of neurulation do not appear to occur in absence of vertical interactions with the organizer (R. Keller et al. , 1992, Dev. Dyn. 193, 218-234). These processes include: (1) cell elongation perpendicular to the plane of the epithelium, forming the neural plate; (2) cell wedging, which rolls the neural plate into a trough; (3) intercalation of two layers of neural plate cells to form one layer; and (4) fusion of the neural folds. To allow planar signaling between all the inducing tissues of the involuting marginal zone and the responding prospective ectoderm, we have designed a "giant sandwich" explant. In these explants, cell elongation and wedging are induced in the superficial neural layer by planar signals without persistent vertical interactions with underlying, involuted mesoderm. A neural trough forms, and neural folds form and approach one another. However, the neural folds do not fuse with one another, and the deep cells of these explants do not undergo their normal behaviors of elongation, wedging, and intercalation between the superficial neural cells, even when planar signals are supplemented with vertical signaling until the late midgastrula (stage 11.5). Vertical interactions with mesoderm during and beyond the late gastrula stage were required for expression of these deep cell behaviors and for neural fold fusion. These explants offer a way to regulate deep and superficial cell behaviors and thus make possible the analysis of the relative roles of these behaviors in closing the neural tube.

Animals↗
PubMed1997

The role of planar and early vertical signaling in patterning the expression of Hoxb-1 in Xenopus.

In this paper we examine the contributions of planar and vertical signaling to the patterning of gene expression in neural development and we examine the routes of this neural induction. We have examined how the expression of Xenopus homeobox gene, Hoxb-1, is regulated by instruction from the mesoderm and/or endoderm and ask whether this instruction is by the vertical or planar routes. We investigated normal expression patterns of Hoxb-1 during early Xenopus development and Hoxb-1 expression in sandwich explants of the dorsal marginal zone, which putatively allow only planar signals to pass from the mesodermal and endodermal tissue (Spemann's organizer) to the prospective neural tissue. In the latter case we found significant variability of expression. Observations during dissections suggested that variable degrees of invasion of the mesodermal-endodermal tissue at the leading edge of the mesodermal mantle might be the cause of this variability. Alternatively, differing lengths of time that the prospective neural region spends in planar contact with tissues of the lateral or ventral regions of the embryo could also contribute to this variability. Analysis of staged Keller sandwich explants, "skewered" sandwiches, in which the degree of contact with underlying, involuted mesoderm-endodermal tissues was marked, and "over-the-pole" and "giant" sandwich explants, in which the degree of planar contact with lateral or ventral tissues was normalized, suggests that both planar and vertical signals are involved in induction and patterning of Hoxb-1 expression. The shift in Hoxb-1 expression from a broad, diffuse pattern to a local, focused pattern, characteristic of the ultimate expression pattern in vivo, does not reflect variable degrees of contact with ventral or lateral tissues, but rather reflects early vertical contact with underlying mesodermal-endodermal tissues. We observed such contact at early gastrula stages (stages 10 to 10+), stages commonly assumed not to have the potential for vertical signaling. As the bottle cells first begin to form, at stage 10-, a massive rotation of the lower involuting marginal zone occurs around an internal lip ("levre interne," Nieuwkoop and Florschutz, 1950). This rotation initiates the formation of the Cleft of Brachet from the floor of the blastocoele and brings the prospective mesoderm and endoderm at the leading edge of the marginal zone into vertical apposition with the prospective neural region quite early in gastrulation. The consequence and importance of recognizing these early internal rearrangements are that it pushes backward the time at which potential vertical inductive interactions between mesoderm and neurectoderm can occur. This means that a purely planar inductive situation can cease to exist as early as the inception of bottle cell formation and that neural patterning through vertical induction starts at the very beginning of gastrulation.

Amino Acid Sequence↗
PubMed1995

Abnormal muscle MRI in a patient with systemic juvenile arthritis.

Although myositis has been described in children with systemic-onset juvenile arthritis (JA), its documentation by MRI has not been reported. We describe a 13-year-old boy with systemic-onset JA, severe myalgia, and elevated muscle enzymes, but normal muscle strength, who had an MRI consistent with myositis. Magnetic resonance imaging can identify the specific location of myositis, allowing more precise definition of a potential complication of systemic JA.

Adolescent↗
PubMed1993

Angel-shaped phalango-epiphyseal dysplasia (ASPED): identification of a new genetic bone marker.

We describe a "new" mild malformation of the phalanx, which we call the "angel-shaped phalanx" (ASP) because of its resemblance to the little angels used for the decoration of Christmas trees. A particular middle phalangeal type of ASPs is found in a distinct variety of multiple epiphyseal dysplasia with marked retardation of bone age and severe coxarthrosis in adult life, previously reported as "hereditary peripheral dysostosis" [Bachman, 1967: Proc R Soc Med 60:21-22; Giedion, 1969: Fortschr Rontgenstr 110:507-524]. However, these authors overlooked the unique configuration of the middle phalanges. We renamed the condition "angel-shaped phalango-epiphyseal dysplasia (ASPED)", which may be transmitted in an autosomal-dominant manner. Six new patients are added, bringing the total to nine patients (two families and two isolated patients). ASPs were seen in five of six children. The ASPs grew into inconspicuous brachydactyly after physeal closure (3/3). The most important additional radiological finding is late and dysplastic development of both femoral heads (5/5), leading to Perthes-like and osteoarthritic changes and severe hip pain in the early thirties (2/2 adults, having reached this age). The marked retardation of carpal bone age may lead to unnecessary clinical evaluation for endocrine disorders. Less frequent clinical manifestations of ASPED are hyperextensibility of the interphalangeal joints (7/9) and hypodontia (4/7). Other types of ASPs are observed in brachyphalangy type C, spondylo-megepiphyseal-metaphyseal dysplasia, and other conditions. The concept of mild bone abnormalities as specific markers for genetic disease, as with cone-shaped epiphyses and now evident in ASPED, may also be useful for ASPs in general.

Adolescent↗
PubMed1991

Killer polyamines?

Mammalian cells can rapidly make large changes in their rate of polyamine biosynthesis in response to mitogenic and trophic signals. However, cultured cells seem to grow adequately as long as they are supplied a steady but unregulated supply of polyamines. This implies that complex and rapid changes in polyamine synthesis serve a function in a special rather than a general biological context. We suggest that the appropriate context in which regulation of polyamines mediates crucial functions is the mammalian embryo and that one function of polyamines is to act as substrate in an oxidative pathway that arbitrates programmed cell death.

Animals↗