Giant Cysts and Cysts with Multiple Central Bodies in Azotobacter vinelandii

Cyst germination in Azotobacter vinelandii ATCC 12837 was studied by using phase contrast and electron microscopy. Germination in this organism was accompanied by the formation of large cyst forms of two different types: giant cysts and cysts containing multiple central bodies. Previously, these two types have been reported only when yeast extract was added to the encystment medium. In this study, we observed giant cysts and cysts with multiple central bodies in nitrogen-free liquid medium. The germination of "normal" cysts is often preceded by enlargement to the giant form and division of the central body to produce cysts with multiple central bodies. Structures similar in appearance to ribosomal aggregates were observed only in cysts undergoing pregermination transformations.     

Sizzled-Tolloid Interactions Maintain Foregut Progenitors by Regulating Fibronectin-Dependent BMP Signaling

The liver, pancreas, and lungs are induced from endoderm progenitors by a series of dynamic growth factor signals from the mesoderm, but how the temporal-spatial activity of these signals is controlled is poorly understood. We have identified an extracellular regulatory loop required for robust bone morphogenetic protein (BMP) signaling in the Xenopus foregut. We show that BMP signaling is required to maintain foregut progenitors and induce expression of the secreted frizzled related protein Sizzled (Szl) and the extracellular metalloprotease Tolloid-like 1 (Tll1). Szl negatively regulates Tll activity to control deposition of a fibronectin (FN) matrix between the mesoderm and endoderm, which is required to maintain BMP signaling. Foregut-specific Szl depletion results in a loss of the FN matrix and failure to maintain robust pSmad1 levels, causing a loss of foregut gene expression and organ agenesis. These results have implications for BMP signaling in diverse contexts and the differentiation of foregut tissue from stem cells.     

Foregut Formation of the Nemerteans and Its Role in Nemertean Systematics

Along a line of the four nemertean orders, Archi-, Palaeo-,Hetero-, and Hoplonemertea established by Iwata, formation ofthe foregut is described in detail on the basis of data hithertorecorded. The axiality of the egg, larva and adult worm of aspecies may change as a function of foregut morphogenesis inthe embryo. During foregut formation the mouth moves from thevegetal pole to the ventral side of the body. In Archinemertea,the larva has an angle of 60° formed by the long axis ofthe body and the foregut, while in Palaeonemertea the angleis 45°. This relationship is retained in the adult. Theplacement of the mouth thus obtained in the larva and adultworm seems to be important for the systematics of the Nemertea,especially for the Archinemertea and Palaeonemertea.     

Foregut microspines in four families of cockroaches (Blattaria)

The microspines of the cockroach foregut were investigated in order to determine their fine structure, variation, patterns of distribution, and possible functions. The following were studied: Blaberidae (4 species), Blatellidae (3 species), Blattidae (2 species), and Cryptocercidae (one species). Elongate microspines (over 30 μm), usually several attached to a basal plate, were found in the buccal cavity and anterior and posterior pharynx of blaberids and blattids, whereas moderate (15–20 μm) to short (1–5 μm) microospines were found in 2 regions in the blattellid and cryptocercid cockroaches. Short microspines (1–5 gmm) individually attached to a basal plate occurred in the esophagus, crop, proventriculus and stomodeal valve regions in all families studied. Microspines appear to be useful in understanding systematics and evolution of cockroaches. The possible role of elongate microspines in retaining food particles during regurgitation behavior is postulated.