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Biomedical subjects

V Prince

Publications and source records attributed to V Prince.

10 recordsLinked to original sources
PubMed2001

Plasticity in zebrafish hox expression in the hindbrain and cranial neural crest.

The anterior-posterior identities of cells in the hindbrain and cranial neural crest are thought to be determined by their Hox gene expression status, but how and when cells become committed to these identities remain unclear. Here we address this in zebrafish by cell transplantation, to test plasticity in hox expression in single cells. We transplanted cells alone, or in small groups, between hindbrain rhombomeres or between the neural crest primordia of pharyngeal arches. We found that transplanted cells regulated hox expression according to their new environments. The degree of plasticity, however, depended on both the timing and the size of the transplant. At later stages transplanted cells were more likely to be irreversibly committed and maintain their hox expression, demonstrating a progressive loss of responsiveness to the environmental signals that specify segmental identities. Individual transplanted cells also showed greater plasticity than those lying within the center of larger groups, suggesting that a community effect normally maintains hox expression within segments. We also raised experimental embryos to larval stages to analyze transplanted cells after differentiation and found that neural crest cells contributed to pharyngeal cartilages appropriate to the anterior-posterior level of the new cellular environment. Thus, consistent with models implicating hox expression in control of segmental identity, plasticity in hox expression correlates with plasticity in final cell fate.

Animals↗
PubMed1998

Zebrafish hox clusters and vertebrate genome evolution.

HOX genes specify cell fate in the anterior-posterior axis of animal embryos. Invertebrate chordates have one HOX cluster, but mammals have four, suggesting that cluster duplication facilitated the evolution of vertebrate body plans. This report shows that zebrafish have seven hox clusters. Phylogenetic analysis and genetic mapping suggest a chromosome doubling event, probably by whole genome duplication, after the divergence of ray-finned and lobe-finned fishes but before the teleost radiation. Thus, teleosts, the most species-rich group of vertebrates, appear to have more copies of these developmental regulatory genes than do mammals, despite less complexity in the anterior-posterior axis.

Animals↗
PubMed1997

Transvestism: a survey of 1032 cross-dressers.

One thousand and thirty-two male periodic cross-dressers (transvestites) responded to an anonymous survey patterned after Prince and Bentler's (1972) report. With few exceptions, the findings are closely related to the 1972 survey results. Eighty-seven percent described themselves as heterosexual. All except 17% had married and 60% were married at the time of this survey. Topics surveyed included demographic, childhood, and family variables, sexual orientation and sexual behavior, cross-gender identity, cross-gender role behavior, future plans to live entirely as a woman, and utilization of counseling or mental health services. Of the present sample, 45% reported seeking counseling compared to 24% of the 1972 survey, and those reporting strong transsexual inclinations were up by 5%. Today's transvestites strongly prefer both their masculine and feminine selves equally. A second research objective was to identify variables discriminating between so-called Nuclear (stable, periodic cross-dressers) and Marginal transvestites (more transgendered or transsexually inclined); 10 strongly discriminating parameters were found. The most important are (i) cross-gender identity, (ii) commitment to live entirely as a woman, (iii) taking steps toward body feminization, (iv) low sexual arousal to cross-dressing. Neither age nor experience as a cross-dresser were found to be correlates of cross-gender identity. Although the present generation of transvestites describe themselves much as did similar subjects 20 years ago, the percentage migrating toward full-time living as a woman is greater.

Adult↗
PubMed1996

Late effects of retinoic acid on neural crest and aspects of rhombomere.

We exposed st.10 chicks to retinoic acid (RA), both globally, and locally to individual rhombomeres, to look at its role in specification of various aspects of hindbrain derived morphology. Previous studies have looked at RA exposure at earlier stages, during axial specification. Stage 10 is the time of morphological segmentation of the hindbrain and is just prior to neural crest migration. Rhombomere 4 localised RA injections result in specific alterations of pathways some crest cells that normally migrate to sites of differentiation of neurogenic derivatives. The r4 crest cells that give rise to mesenchymal derivatives are unaffected. In addition, r4 gene expression is also partially altered by RA; within 6 hours of r4 exposure to RA, ectopic expression of Krox-20 is seen in r4 and Hoxb-1 expression is lost while Hoxa-2 expression continues normally. When we examined these RA-treated animals later in development, they showed an anterior displacement of the facial ganglion in addition to a mis-direction of the extensions of its distal axons and a dramatic decrease in the number of contralateral vestibuloacoustic neurons normally seen in r4. Only this r4-specific neuronal type is affected in r4; the motor neuron projections seem normal in experimental animals. The specificity of this result, combined with the loss of Hoxb-1 expression in r4 and the work by Krumlauf and co-workers showing gain of contralateral neurons co-localised with ectopic Hoxb-1 expression, indicates a role for Hoxb-1 and RA in the specification of this cell type in normal development. These results suggest that RA, at st.10, is able to affect some aspects of segment identity while leaving others unchanged.

Animals↗
PubMed1994

Hoxa-2 expression in normal and transposed rhombomeres: independent regulation in the neural tube and neural crest.

In this study we have cloned the chick Hoxa-2 gene and analysed its expression during early development. We find that Hoxa-2 has a rostral limit of expression in the rhombencephalic neural tube corresponding precisely to the boundary between rhombomeres (r)1 and 2; a limit further rostral than any other Hox gene reported to date. Neural crest migrates from r2 to populate the first branchial arch, yet although Hoxa-2 is expressed down the full dorsoventral extent of r2 during the phase of neural crest emigration, there is no Hoxa-2 expression in either the emergent neural crest or in the first branchial arch. Conversely, at the level of r4, both the neural tube and the neural crest cells, which migrate out of this rhombomere to populate the second branchial arch, express Hoxa-2. Other Hox genes expressed in the rhombencephalic neural tube demonstrate a transfer of expression from neural tube to neural crest at all axial levels of expression. Hoxa-2 is thus unusual in demonstrating separate anterior expression limits in neural tube and neural crest; this allowed us to test whether Hox gene expression patterns in neural crest are determined by migratory pathways or are prespecified by the site of origin in the neuroepithelium. Grafting experiments in which pairs of rhombomeres were transplanted to ectopic sites at the time of rhombomere boundary formation reveal a prepatterning of the neural crest with respect to Hoxa-2 expression. The decision to down-regulate Hoxa-2 expression in r2-derived neural crest, but to maintain Hoxa-2 expression in r4-derived neural crest is intrinsic to the premigratory crest cell population. Thus, following grafting of r4 to the r2 site and vice-versa, Hoxa-2 expression is maintained in r4-derived neural crest, but lost in r2-derived neural crest.

Animals↗
PubMed1993

Selective dispersal of avian rhombomere cells in orthotopic and heterotopic grafts.

During hindbrain development, cells become segregated into segmental groups, rhombomeres, by mechanisms that are presently unknown. One contributory factor early in development may be an alternating periodicity in cell surface properties down the neuraxis. This possibility was previously suggested by experiments in which tissue from different segmental levels was apposed in the absence of a boundary. New boundaries were regenerated only when rhombomeres from adjacent positions or positions three rhombomeres distant from one another were apposed. Combinations of two odd-numbered or two even-numbered rhombomeres usually failed to generate a boundary. In order to pursue this phenomenon to the cellular level, we have used two approaches, both involving donor-to-host transplantation. First, quail rhombomeres were grafted at various hindbrain levels of a chick host. Apposition of rhombomere 4 (r4) with r3 was concomitant with negligible cell mixing across the interface. By contrast, combinations of r3 with r5 or with r3 tissue led to cell mixing that was more extensive in combinations of identical rhombomeres (r3 with r3) than between two alternate ones (r3 with r5). Secondly, we grafted small pieces of fluorescently prelabelled chick rhombomere tissue at various hindbrain levels of chick hosts. In most cases, cells dispersed widely when transplanted orthopically or two segments distant from that of their origin. Cells transplanted into an adjacent segment, however, showed a tendency to remain undispersed. Among the different graft combinations, furthermore, there was a variation in the extent of dispersal that showed an additional level of complexity not revealed in boundary regeneration experiments. The possibility is raised that the early partitioning of rhombomeres involves a hierarchy in the adhesive preferences of cell-cell interactions along the neuraxis.

Animals↗
PubMed1988

Aerial Dispersal and Epiphytic Survival of Pseudomonas syringae during a Pretest for the Release of Genetically Engineered Strains into the Environment.

Prospective experimental field evaluation of genetically engineered microorganisms, such as microbial pest control agents, raises issues of how to properly ascertain their fate and survival in the environment. Field trials with recombinant organisms must reflect requirements for sampling and monitoring. Field trials were conducted at Tulelake, Calif., to monitor the numbers of viable cells of a nonrecombinant strain of Pseudomonas syringae that entered the atmosphere and landed on plants and soil during and after an aerosol spray application. An exponential decrease in numbers of viable cells deposited at increasing distances from three sprayed plots was observed. The relative rate of survival of cells sprayed directly on plants was more than 10 times higher than that of cells dispersed through the air to similar adjacent plants. Results are being used to gain experience with the characteristics of a release site that influence containment or dispersal and to develop appropriate sampling methodologies for evaluating survival and dispersal characteristics of genetically engineered bacteria released into the environment. The ability to make predictions about microbial dispersal and survival will reduce the uncertainties associated with environmental releases of recombinant organisms.

Journal Article↗