Stiffness of primordial germ cells is required for their extravasation in avian embryos.

Unlike mammals, primordial germ cells (PGCs) in avian early embryos exploit blood circulation to translocate to the somatic gonadal primordium, but how circulating PGCs undergo extravasation remains elusive. We demonstrate with single-cell level live-imaging analyses that the PGCs are arrested at a specific site in the capillary plexus, which is predominantly governed by occlusion at a narrow path in the vasculature. The occlusion is enabled by a heightened stiffness of the PGCs mediated by actin polymerization.

Nodal signaling regulates asymmetric cellular behaviors, driving clockwise rotation of the heart tube in zebrafish.

Clockwise rotation of the primitive heart tube, a process regulated by restricted left-sided Nodal signaling, is the first morphological manifestation of left-right asymmetry. How Nodal regulates cell behaviors to drive asymmetric morphogenesis remains poorly understood. Here, using high-resolution live imaging of zebrafish embryos, we simultaneously visualized cellular dynamics underlying early heart morphogenesis and resulting changes in tissue shape, to identify two key cell behaviors: cell rearrangement and cell shape change, which convert initially flat heart primordia into a tube through convergent extension.

The heart tube forms and elongates through dynamic cell rearrangement coordinated with foregut extension.

In the initiation of cardiogenesis, the heart primordia transform from bilateral flat sheets of mesoderm into an elongated midline tube. Here, we discover that this rapid architectural change is driven by actomyosin-based oriented cell rearrangement and resulting dynamic tissue reshaping (convergent extension, CE). By labeling clusters of cells spanning the entire heart primordia, we show that the heart primordia converge toward the midline to form a narrow tube, while extending perpendicularly to rapidly lengthen it.

A complex choreography of cell movements shapes the vertebrate eye.

Optic cup morphogenesis (OCM) generates the basic structure of the vertebrate eye. Although it is commonly depicted as a series of epithelial sheet folding events, this does not represent an empirically supported model. Here, we combine four-dimensional imaging with custom cell tracking software and photoactivatable fluorophore labeling to determine the cellular dynamics underlying OCM in zebrafish.

Time-lapse analysis reveals local asymmetrical changes in C-looping heart tube.

Heart development has long served as a model system of left-right asymmetrical morphogenesis, and many key laterality genes have been shown to be involved in the process of asymmetrical heart looping. We established a time-lapse imaging system to observe the process of C-looping during chick heart development, and our observations showed that the C-looping is a very complicated process that involves several local changes in shape: the process can be divided into dextral rotation of the rostral and caudal segments with ventral bending in the rostral part and horizontal anti-clockwise rotation with enlargement of the left part in the caudal segment. Further experimental manipulations revealed characteristics of these morphological changes and regional interactions for the events, and we propose that asymmetrical enlargement of the caudal part is one of the targets of the laterality genes in the C-looping process.

Development of thyroid-stimulating hormone beta subunit-producing cells in the chicken embryonic pituitary gland.

In previous studies, the distribution of thyrotropes in the chicken pituitary gland has been analyzed by immunohistochemistry using heterologous antibodies. In this study, we examined the distribution of thyroid-stimulating hormone beta subunit-immunopositive (TSHbeta-ip) cells and the expression of TSHbeta mRNA in the pituitary glands of chicken embryos by immunohistochemistry using a specific antiserum to the chicken TSHbeta, in situ hybridization and RT-PCR. Immunohistochemical and morphometric analyses revealed that the TSHbeta-ip cells first appeared on embryonic day 10 (E10) in the pituitary gland and were mainly distributed in the cephalic lobe and that the cell density on E20 was almost 4 times greater than that on E10.