Free volume theory explains the unusual behavior of viscosity in a non-confluent tissue during morphogenesis.

A recent experiment on zebrafish blastoderm morphogenesis showed that the viscosity (η) of a non-confluent embryonic tissue grows sharply until a critical cell packing fraction (ϕS). The increase in η up to ϕS is similar to the behavior observed in several glass-forming materials, which suggests that the cell dynamics is sluggish or glass-like. Surprisingly, η is a constant above ϕS. To determine the mechanism of this unusual dependence of η on ϕ, we performed extensive simulations using an agent-based model of a dense non-confluent two-dimensional tissue. We show that polydispersity in the cell size, and the propensity of the cells to deform, results in the saturation of the available free area per cell beyond a critical packing fraction. Saturation in the free space not only explains the viscosity plateau above ϕS but also provides a relationship between equilibrium geometrical packing to the dramatic increase in the relaxation dynamics.

The ftz upstream element drives late ftz stripes but is not required for regulation of Ftz target genes.

The regulation of gene expression in precise, rapidly changing spatial patterns is essential for embryonic development. Multiple enhancers have been identified for the evolving expression patterns of the cascade of Drosophila segmentation genes that establish the basic body plan of the fly. Classic reporter transgene experiments identified multiple cis-regulatory elements (CREs) that are sufficient to direct various aspects of the evolving expression pattern of the pair-rule gene fushi tarazu (ftz). These include enhancers that coordinately activate expression in all seven stripes and stripe-specific elements that activate expression in one or more ftz stripes. Of the two 7-stripe enhancers, analysis of reporter transgenes demonstrated that the upstream element (UPS) is autoregulatory, requiring direct binding of Ftz protein to direct striped expression. Here, we asked about the endogenous role of the UPS by precisely deleting this 7-stripe enhancer. In ftzΔUPS7S homozygotes, ftz stripes appear in the same order as wildtype, and all but stripe 4 are expressed at wildtype levels by the end of the cellular blastoderm stage. This suggests that the zebra element and UPS harbor information to direct stripe 4 expression, although previous deletion analyses failed to identify a stripe-specific CRE within these two 7-stripe enhancers. However, the UPS is necessary for late ftz stripe expression, with all 7 stripes decaying earlier than wildtype in ftzΔUPS7S homozygotes. Despite this premature loss of ftz expression, downstream target gene regulation proceeds as in wildtype, and segmentation is unperturbed in the overwhelming majority of animals. We propose that this late-acting enhancer provides a buffer against perturbations in gene expression but is not required for establishment of Ftz cell fates. Overall, our results demonstrate that multiple enhancers, each directing distinct aspects of an overall gene expression pattern, contribute to fine-tuning the complex patterns necessary for embryonic development.

Utilization of central disk of blastoderm and germinal crescent region for production of interspecific germline chimera between chicken and quail / 亚洲男科学杂志(英文版)

<p><b>AIM</b>The production of interspecific germline chimeras between chicken and quail were attempted employing the dissociated cells derived from the blastodermal central disk (stage X) and the germinal crescent region of embryo (stage 7-8).</p><p><b>METHODS</b>The central disk (CD) of the area pellucida in chicken blastoderm (stage X) and the germinal crescent region (GCR) of embryo (stage 7-8) were dispersed and injected into the subgerminal cavity of quail blastoderm (stage X). Injected eggs were incubated for 7 days or to hatching. The donor chicken DNA was detected by the polymerase chain reaction.</p><p><b>RESULTS</b>In day-7 embryos, chicken DNA was detected in 5 gonads and 9 brains from 53 survived embryos received chicken CD cells, and 1 gonads and 6 brains from 27 survived embryos received chicken GCR. Chicken DNA was also detected from the semen of one adult male hatched from eggs received chicken GCR cells.</p><p><b>CONCLUSION</b>CD and GCR cells as the donors showed the possibility to produce the interspecific germline chimera, but further studies are needed to make necessary improvement.</p>

Two Cases of Testicular Teratoma / 대한비뇨기과학회지

Teratoma of the testis is a type of mixed tumor made up of various kinds of tissue representing the three primitive layers of blastoderm. Recently we experienced two cases of testicular teratoma in 23-year-old male patients, so we report these two cases of testicular teratoma with review of literatures.