Switching the rate and pattern of cell division for neural tube closure

Imaging developmental cell cycles

The last decade has seen a major expansion in development of live biosensors, the tools needed to genetically encode them into model organisms, and the microscopic techniques used to visualize them. When combined, these offer us powerful tools with which to make fundamental discoveries about complex biological processes. In this review, we summarize the availability of biosensors to visualize an essential cellular process, the cell cycle, and the techniques for single-cell tracking and quantification of these reporters. We also highlight studies investigating the connection of cellular behavior to the cell cycle, particularly through live imaging, and anticipate exciting discoveries with the combination of these technologies in developmental contexts.

p53 Disruption Increases Uracil Accumulation in DNA of Murine Embryonic Fibroblasts and Leads to Folic Acid-Nonresponsive Neural Tube Defects in Mice

BACKGROUND

Neural tube defects (NTDs) occur in nervous tissue during embryogenesis when the neural tube fails to close. Approximately 70% of all human NTDs can be prevented by folic acid (FA). Altered expression and/or function of the tumor suppressor protein p53 can lead to NTDs in mouse models.

OBJECTIVES

The aim of this study was to determine if dietary FA could rescue p53-/--induced NTDs in mice, and to determine the effect loss of p53 has on pathways in folate 1-carbon metabolism.

METHODS

p53+/- female mice were randomly allocated and weaned onto either an FA-sufficient diet (2 mg/kg folic acid; +FA), or an FA-deficient diet (-FA). After 8 wk, the females were time-mated to p53-/- males. Embryos were examined at E12.5 for NTDs. Folate enzyme concentrations, nucleotide synthesis, uracil accumulation in DNA, and proliferation were measured in primary murine embryonic fibroblasts (MEFs). The "n - 1" chi-square test was used to compare NTD percentages, whereas all other data were analyzed by Student t test, except where noted a multilevel-fit model was used.

RESULTS

NTD rates of litters from dams consuming the +FA diet (20/46; 43%) did not differ from those of litters from dams consuming the -FA diet (14/35; 40%) (P > 0.05). p53-/- MEFs had 55% higher rates of folate-dependent de novo dTMP synthesis, a ∼2-fold higher accumulation of uracil in DNA, and a ∼30% higher rate of proliferation (P ≤ 0.05) than p53+/- MEFs independent of folate.

CONCLUSIONS

p53-related NTDs are not FA responsive. Increased dTMP synthesis in p53-/- MEFs might not have been sufficient to meet the demands for thymidine triphosphate (dTTP) synthesis as evidenced by the elevated amounts of uracil in DNA. This study provides additional evidence that elevated uracil in DNA is a risk factor for NTDs.

Development of the human penis and clitoris

The human penis and clitoris develop from the ambisexual genital tubercle. To compare and contrast the development of human penis and clitoris, we used macroscopic photography, optical projection tomography, light sheet microscopy, scanning electron microscopy, histology and immunohistochemistry. The human genital tubercle differentiates into a penis under the influence of androgens forming a tubular urethra that develops by canalization of the urethral plate to form a wide diamond-shaped urethral groove (opening zipper) whose edges (urethral folds) fuse in the midline (closing zipper). In contrast, in females, without the influence of androgens, the vestibular plate (homologue of the urethral plate) undergoes canalization to form a wide vestibular groove whose edges (vestibular folds) remain unfused, ultimately forming the labia minora defining the vaginal vestibule. The neurovascular anatomy is similar in both the developing human penis and clitoris and is the key to successful surgical reconstructions.