Biomedical subjects

F Rudolf Turner

Publications and source records attributed to F Rudolf Turner.

7 recordsLinked to original sources

PubMed2006

Cellular and subcellular structure of neoproterozoic animal embryos.

Stereoblastic embryos from the Doushantuo Formation of China exhibit occasional asynchronous cell division, with diminishing blastomere volume as cleavage proceeded. Asynchronous cell division is common in modern embryos, implying that sophisticated mechanisms for differential cell division timing and embryonic cell lineage differentiation evolved before 551 million years ago. Subcellular structures akin to organelles, coated yolk granules, or lipid vesicles occur in these embryos. Paired reniform structures within embryo cells may represent fossil evidence of cells about to undergo division. Embryos exhibit no evidence of epithelial organization, even in embryos composed of approximately 1000 cells. Many of these features are compatible with metazoans, but the absence of epithelialization is consistent only with a stem-metazoan affinity for Doushantuo embryos.

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PubMed2006

Experimental taphonomy shows the feasibility of fossil embryos.

The recent discovery of apparent fossils of embryos contemporaneous with the earliest animal remains may provide vital insights into the metazoan radiation. However, although the putative fossil remains are similar to modern marine animal embryos or larvae, their simple geometric forms also resemble other organic and inorganic structures. The potential for fossilization of animals at such developmental stages and the taphonomic processes that might affect preservation before mineralization have not been examined. Here, we report experimental taphonomy of marine embryos and larvae similar in size and inferred cleavage mode to presumptive fossil embryos. Under conditions that prevent autolysis, embryos within the fertilization envelope can be preserved with good morphology for sufficiently long periods for mineralization to occur. The reported fossil record exhibits size bias, but we show that embryo size is unlikely to be a major factor in preservation. Under some conditions of death, fossilized remains will not accurately reflect the cell structure of the living organism. Although embryos within the fertilization envelope have high preservation potential, primary larvae have negligible preservation potential. Thus the paleo-embryological record may have strong biases on developmental stages preserved. Our data provide a predictive basis for interpreting the fossil record to unravel the evolution of ontogeny in the origin of metazoans.

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PubMed2005

The proximal region of the beta-tubulin C-terminal tail is sufficient for axoneme assembly.

We have used Drosophila testis-specific beta2-tubulin to determine sequence requirements for different microtubules. The beta2-tubulin C-terminal tail has unique sperm-specific functions [Dev Biol 158:267-286 (2003)] and is also important for forming stable heterodimers with alpha-tubulin, a general function common to all microtubules [Mol Biol Cell 12(7):2185-2194 (2001)]. beta-tubulins utilized in motile 9 + 2 axonemes contain a C-terminal sequence "axoneme motif" [Science 275 (1997) 70-73]. C-terminal truncated beta2-tubulin cannot form the sperm tail axoneme. Here we show that a partially truncated beta2-tubulin (beta2Delta7) containing only the proximal portion of the C-terminal tail, including the axoneme motif, can support production of functional motile sperm. We conclude that these proximal eight amino acids specify the binding site for protein(s) essential to support assembly of the motile axoneme. Males that express beta2Delta7, although they are fertile, produce fewer sperm than wild type males. Beta2Delta7 causes a slightly increased error rate in spermatogenesis attributable to loss of stabilizing properties intrinsic to the full-length C-terminal tail. Therefore, beta2Delta7 males would be at a selective disadvantage and it is likely that the full-length C-terminus would be essential in the wild and in evolution.

Amino Acid Sequence↗

PubMed2004

CREB binding protein functions during successive stages of eye development in Drosophila.

During the development of the compound eye of Drosophila several signaling pathways exert both positive and inhibitory influences upon an array of nuclear transcription factors to produce a near-perfect lattice of unit eyes or ommatidia. Individual cells within the eye are exposed to many extracellular signals, express multiple surface receptors, and make use of a large complement of cell-subtype-specific DNA-binding transcription factors. Despite this enormous complexity, each cell will make the correct developmental choice and adopt the appropriate cell fate. How this process is managed remains a poorly understood paradigm. Members of the CREB binding protein (CBP)/p300 family have been shown to influence development by (1) acting as bridging molecules between the basal transcriptional machinery and specific DNA-binding transcription factors, (2) physically interacting with terminal members of signaling cascades, (3) acting as transcriptional coactivators of downstream target genes, and (4) playing a key role in chromatin remodeling. In a screen for new genes involved in eye development we have identified the Drosophila homolog of CBP as a key player in both eye specification and cell fate determination. We have used a variety of approaches to define the role of CBP in eye development on a cell-by-cell basis.

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PubMed2002

The centrosome is a dynamic structure that ejects PCM flares.

The Drosophila Centrosomin (Cnn) protein is an essential core component of centrosomes in the early embryo. We have expressed a Cnn-GFP fusion construct in cleavage stage embryos, which rescues the maternal effect lethality of cnn mutant animals. The localization patterns seen with GFP-Cnn are identical to the patterns we see by immunofluorescent staining with anti-Cnn antibodies. Live imaging of centrosomes with Cnn-GFP reveals surprisingly dynamic features of the centrosome. Extracentrosomal particles of Cnn move radially from the centrosome and frequently change their direction. D-TACC colocalized with Cnn at these particles. We have named these extrusions 'flares'. Flares are dependent on microtubules, since disruption of the microtubule array severs the movement of these particles. Movement of flare particles is cleavage-cycle-dependent and appears to be attributed mostly to their association with dynamic astral microtubules. Flare activity decreases at metaphase, then increases at telophase and remains at this higher level of activity until the next metaphase. Flares appear to be similar to vertebrate PCM-1-containing 'centriolar satellites' in their behavior. By injecting rhodamine-actin, we observed that flares extend no farther than the actin cage. Additionally, disruption of the microfilament array increased the extent of flare movement. These observations indicate that centrosomes eject particles of Cnn-containing pericentriolar material that move on dynamic astral microtubules at a rate that varies with the cell cycle. We propose that flare particles play a role in organizing the actin cytoskeleton during syncytial cleavage.

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PubMedDate not supplied

Regulatory punctuated equilibrium and convergence in the evolution of developmental pathways in direct-developing sea urchins.

We made hybrid crosses between closely and distantly related sea urchin species to test two hypotheses about the evolution of gene regulatory systems in the evolution of ontogenetic pathways and larval form. The first hypothesis is that gene regulatory systems governing development evolve in a punctuational manner during periods of rapid morphological evolution but are relatively stable over long periods of slow morphological evolution. We compared hybrids between direct and indirect developers from closely and distantly related families. Hybrids between eggs of the direct developer Heliocidaris erythrogramma and sperm of the 4-million year distant species H. tuberculata, an indirect developer, restored feeding larval structures and paternal gene expression that were lost in the evolution of the direct-developing maternal parent. Hybrids resulting from the cross between eggs of H. erythrogramma and sperm of the 40-million year distant indirect-developer Pseudoboletia maculata are strikingly similar to hybrids between the congeneric hybrids. The marked similarities in ontogenetic trajectory and morphological outcome in crosses of involving either closely or distantly related indirect developing species indicates that their regulatory mechanisms interact with those of H. erythrogramma in the same way, supporting remarkable conservation of molecular control pathways among indirect developers. Second, we tested the hypothesis that convergent developmental pathways in independently evolved direct developers reflect convergence of the underlying regulatory systems. Crosses between two independently evolved direct-developing species from two 70-million year distant families, H. erythrogramma and Holopneustes purpurescens, produced harmoniously developing hybrid larvae that maintained the direct mode of development and did not exhibit any obvious restoration of indirect-developing features. These results are consistent with parallel evolution of direct-developing features in these two lineages.

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PubMedDate not supplied

Major regulatory factors in the evolution of development: the roles of goosecoid and Msx in the evolution of the direct-developing sea urchin Heliocidaris erythrogramma.

The transcription factors Gsc and Msx are expressed in the oral ectoderm of the indirect-developing sea urchin Heliocidaris tuberculata. Their patterns of expression are highly modified in the direct developer Heliocidaris erythrogramma, which lacks an oral ectoderm. We here test the hypothesis that they are large effect genes responsible for the loss of the oral ectoderm module in the direct-developing larva of H. erythrogramma as well as for the restoration of an overt oral ectoderm in H.e. xH.t. hybrids. We undertook misexpression/overexpression and knockdown assays in the two species and in hybrids by mRNA injection. The results indicate that dramatic changes of function of these transcription factors has occurred. One of these genes, Gsc, has the ability when misexpressed to partially restore oral ectoderm in H. erythrogramma. On the other hand, Msx has lost any oral function and instead has a role in mesoderm proliferation and patterning. In addition, we found that the H. tuberculataGsc is up regulated in H.e. xH.t. hybrids, showing a preferential use of the indirect developing parental gene in the development of the hybrid. We suggest that Gsc qualifies as a gene of large evolutionary effect and is partially responsible for the evolution of direct development of H. erythrogramma. We discuss these results in light of modularity and genetic networks in development, as well as in their implications for the rapid evolution of large morphological changes in development.

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