Stage-dependent sequential organization of nascent smooth muscle cells and its implications for the gut coiling morphogenesis in Xenopus larva.

In vertebrates, gut coiling proceeds left-right asymmetrically during expansion of the gastrointestinal tract with highly organized muscular structures facilitating peristalsis. In this report, we explored the mechanisms of larval gut coiling morphogenesis relevant to its nascent smooth muscle cells using highly transparent Xenopus early larvae. First, to visualize the dynamics of intestinal smooth muscle cells, whole-mount specimens were immunostained with anti-smooth muscle-specific actin (SM-actin) antibody.

Visualisation of cerebrospinal fluid flow patterns in albino Xenopus larvae in vivo.

Background: It has long been known that cerebrospinal fluid (CSF), its composition and flow, play an important part in normal brain development, and ependymal cell ciliary beating as a possible driver of CSF flow has previously been studied in mammalian fetuses in vitro. Lower vertebrate animals are potential models for analysis of CSF flow during development because they are oviparous. Albino Xenopus laevis larvae are nearly transparent and have a straight, translucent brain that facilitates the observation of fluid flow within the ventricles.

Invasion by matrix metalloproteinase-expressing cells is important for primitive streak formation in early chick blastoderm.

Epiblast cells in the early chick embryo differentiate to form all three germ layers through ingression of cells at the primitive streak across the basement membrane that underlies the epiblast. We tested the idea that degradation of the extracellular matrix components by matrix metalloproteinase(s) (MMPs) is involved in this process. Epiblast cells and primitive streak cells were dissociated into single cells and seeded onto a reconstituted basement membrane gel in vitro.

Optic chiasm in the species of order Clupeiformes, family Clupeidae: optic chiasm of Spratelloides gracilis shows an opposite laterality to that of Etrumeus teres.

In most teleost fishes, the optic nerves decussate completely as they project to the mesencephalic region. Examination of the decussation pattern of 25 species from 11 different orders in Pisces revealed that each species shows a specific chiasmic type. In 11 species out of the 25, laterality of the chiasmic pattern was not determined; in half of the individuals examined, the left optic nerve ran dorsally to the right optic nerve, while in the other half, the right optic nerve was dorsal.

Subtilisin-like proprotein convertase activity is necessary for left-right axis determination in Xenopus neurula embryos.

Signaling by members of TGF-beta superfamily requires the activity of a family of site-specific endopeptidases, known as Subtilisin-like proprotein convertases (SPCs), which cleave these ligands into mature, active forms. To explore the role of SPCs in lateral plate mesoderm (LPM) differentiation in Xenopus, two SPC inhibitors, decanoyl-Arg-Val-Lys-Arg-chloromethylketone (Dec-RVKR-CMK) and hexa-arginine, were injected into the left and right LPM of Xenopus neurulae. Left-side injection caused heart-specific left-right reversal, and this phenotype was rescued by co-injection of mature Nodal protein.

Xenopus nodal related-1 is indispensable only for left-right axis determination.

In Xenopus, multiple nodal-related genes are expressed in the organizer region. Among them, only Xenopus nodal related-1 (Xnr-1) is expressed unilaterally in the left lateral plate mesoderm (LPM) at late neurula-early tailbud stage. To elucidate the essential role of Xnr-1 for left-right specification, loss of function experiments using antisense morpholino oligonucleotides (MOs) targeting three different regions of Xnr-1 were performed.

Xenopus neurula left-right asymmetry is respeficied by microinjecting TGF-beta5 protein.

A variety of TGF-beta-related ligands regulate the left-right asymmetry of vertebrates but the involvement of TGF-betas in left-right specification has not been reported. We assessed whether TGF-beta signaling is involved in the left-right specification of Xenopus post-gastrula embryos by microinjecting Xenopus TGF-beta5 protein into the left or right flank of neurula-tailbud embryos. Injection on the right side of neurulae caused left-right reversal of the internal organs in 93% of the embryos, while injection on the left side caused less than 5% left-right reversal.

Invasion and migration of a single chick pre-streak stage epiblast cell in vitro: Its implication to the primitive streak formation.

To investigate the contribution of the epiblast cell behavior to the primitive streak formation, we examined the motility of a single epiblast cell from pre-streak stage embryo in vitro. On the substratum that was evenly coated with laminin gel, epiblast cells attached well to the gel and one or a few very long and broad cellular processes protruded from their spherical cell bodies; however, they hardly locomoted on it. Unexpectedly, after overnight culture, half of the single cells dissolved the laminin gel beneath them to make well-like holes, and invaded in the holes.

Morphometry of cellular protrusions of mesodermal cells and fibrous extracellular matrix in the primitive streak stage chick embryo.

Chick mesodermal cells, having become invaginated and beginning to locomote prior to the formation of the mesodermal cell layer at an early primitive streak stage, extend many filopodia and flatten themselves against the basal surface of the epiblast. Morphometry on scanning electron micrographs of chick mesodermal cells revealed two statistically significant tendencies. Each cell took an extended form and protruded filopodia, preferably along its major axis, suggesting that the force extending the cell body was generated by both ends rich in filopodia.