Degradation of hyaluronan by a Hyal2-type hyaluronidase affects pattern formation of vitelline vessels during embryogenesis of Xenopus laevis.
A Hyal2-type hyaluronidase of Xenopus laevis (Xhyal2) was characterized by molecular cloning, biochemical analysis and ectopic overexpression in embryos. When expressed in Xenopus oocytes, Xhyal2 exists as a soluble protein in the extracellular space and in intercellular compartments as well as being attached to the cell surface through a glycosyl-phosphatidyl-inositol anchor. This enzyme specifically degrades hyaluronan not only at acidic pH values but more slowly also under physiological conditions. Xhyal2 is differentially expressed during embryogenesis. Particularly striking is the high level of expression in the developing brain, the head mesenchyme and the pronephros. Elevated levels of mRNA were also found in endothelial cells which will later form vascular structures. Ectopic overexpression of Xhyal2 in frog embryos causes loss of hyaluronan in the cellular environment. This causes severe defects in the assembly of the highly structured plexus of the vitelline vessels from prevascular endothelial cells. Our data support the notion that the level of Xhyal2 expression determines the organization of the extracellular environment so that cells can merge and/or migrate within an originally impenetrable matrix. (+info)
Oviductin, the oviductal protease that mediates gamete interaction by affecting the vitelline coat in Bufo japonicus: its molecular cloning and analyses of expression and posttranslational activation.
Previous studies indicated that the acquisition of egg fertilizability during transit through the pars recta portion of the oviduct in Bufo japonicus is accompanied by hydrolytic conversion of the vitelline coat 40- to 52-kDa components to 39-kDa components induced by a 66-kDa serine protease, "oviductin." In this study, we cloned a 3028-bp cDNA that contained an open reading frame encoding 974 amino acids with a calculated molecular mass of 107.6 kDa, including two protease domains and three repeats of CUB domains. Sequence analysis indicated that the catalytically active 66-kDa protein comprised an N-terminally located oviductin protease and two CUB domains. The oviductin gene was transcribed as a part of 6-kb mRNA that was expressed specifically in the cells lining the bottom of epithelial folds in the oviductal pars recta, and this expression was highly accelerated when the pars recta fragments were cultured in the presence of hCG. Western blot analyses using antibodies against a protease domain revealed that the catalytically inactive 102-kDa proteins in the pars recta granules yield 66-kDa catalytically active and 82- and 59-kDa inactive molecules. We propose that the oviductin translated as 107.6-kDa precursors are processed both N- and C-terminally to give rise to a 66-kDa active form comprising a serine protease and two CUB domains. (+info)
Changes in the spermatozoon during fertilization in Hydroides hexagonus (Annelida). I. Passage of the acrosomal region through the vitelline membrane.
In the previous paper the structure of the acrosomal region of the spermatozoon was described. The present paper describes the changes which this region undergoes during passage through the vitelline membrane. The material used consisted of moderately polyspermic eggs of Hydroides hexagonus, osmium-fixed usually 9 seconds after insemination. There are essentially four major changes in the acrosome during passage of the sperm head through the vitelline membrane. First, the acrosome breaks open apically by a kind of dehiscence which results in the formation of a well defined orifice. Around the lips of the orifice the edges of the plasma and acrosomal membranes are then found to be fused to form a continuous membranous sheet. Second, the walls of the acrosomal vesicle are completely everted, and this appears to be the means by which the apex of the sperm head is moved through the vitelline membrane. The lip of the orifice comes to lie deeper and deeper within the vitelline membrane. At the same time the lip itself is made up of constantly changing material as first the material of the outer zone and then that of the intermediate zone everts. One is reminded of the lip of an amphibian blastopore, which during gastrulation maintains its morphological identity as a lip but is nevertheless made up of constantly changing cells, with constantly changing outline and even constantly changing position. Third, the large acrosomal granule rapidly disappears. This disappearance is closely correlated with a corresponding disappearance of a part of the principal material of the vitelline membrane from before it, and the suggestion is made that the acrosomal granule is the source of the lysin which dissolves this part of the vitelline membrane. Fourth, in the inner zone the fifteen or so short tubular invaginations of the acrosomal membrane, present in the normal unreacted spermatozoon, lengthen considerably to become a tuft of acrosomal tubules. These tubules are the first structures of the advancing sperm head to touch the plasma membrane of the egg. It is notable that the surface of the acrosomal tubules which once faced into the closed acrosomal cavity becomes the first part of the sperm plasma membrane to meet the plasma membrane of the egg. The acrosomal tubules of Hydroides, which arise simply by lengthening of already existing shorter tubules, are considered to represent the acrosome filaments of other species. (+info)
In ovo vitelline duct ligation results in transient changes of bursal microenvironments.
The avian bursa of Fabricius has a direct connection to the cloaca via the bursal duct. Using the bursal duct ligation technique, it has been clearly shown that the B cells of the bursal follicles develop under the influence of cloacal antigens. These antigens have been suggested to be present on the bursal secretory dendritic cells in immunoglobulin G (IgG)-containing complexes. We studied the effect of maternal (yolk) antigens on the early development of B cells and the appearance of IgG-containing complexes of the bursal dendritic cells with a novel embryo manipulation technique, in ovo vitelline duct ligation. This operation blocked the direct (intestinal) transport of yolk substances into the intestine, but left the vitelline circulation intact. Vitelline duct ligation performed on embryonic day 17 resulted in serious but transient bursal underdevelopment during the first week of life: (1) IgG and the follicular dendritic cell marker 74.3 were not detectable on the bursal secretory dendritic cells, in spite of a normal serum IgG level and free communication with the cloacal lumen; (2) the number of B cells in the follicles was greatly reduced and they showed an altered phenotype, resembling that of the prebursal B cells. The intracloacal administration of different proteins effectively restored the bursal phenotype. These data suggest that maternal antigens indirectly help the maturation of bursal secretory dendritic cells and concomitantly that of B cells during the first week of life. (+info)
Adult case of an omphalomesenteric cyst resected by laparoscopic-assisted surgery.
This report describes an extremely rare adult case of an omphalomesenteric cyst resected by laparoscopic-assisted surgery. A 29-years-old Japanese man was referred and admitted to Kyushu University Hospital because of an abdominal mass and an elevated serum CEA (carcinoembryonic antigen) level (21.3 ng/mL) in August 2001. Abdominal CT and US demonstrated a cystic mass with septum and calcification. Laparoscopy showed a large mass to be attached to his abdominal wall, measuring 110 mm x 70 mm x 50 mm and filled with mucus. The mass was resected by laparoscopic-assisted surgery. The histological findings of its wall showed fibromuscular tissue, adipose tissue, calcification, and an intestinal structure. It was finally diagnosed to be an omphalomesenteric cyst. (+info)
pVHL function is essential for endothelial extracellular matrix deposition.
The tumor suppressor von Hippel-Lindau protein (pVHL) is critical for cellular molecular oxygen sensing, acting to target degradation of the hypoxia-inducible factor alpha transcription factor subunits under normoxic conditions. We have found that independent of its function in regulating hypoxic response, the VHL gene plays a critical role in embryonic endothelium development through regulation of vascular extracellular matrix assembly. We created mice lacking the VHL gene in endothelial cells; these conditional null mice died at the same stage as homozygous VHL-null mice, with similar vascular developmental defects. These included defective vasculogenesis in the placental labyrinth, a collapsed endocardium, and impaired vessel network patterning. The defects in embryonic vascularization were correlated with a diminished vascular fibronectin deposition in vivo and defective endothelial extracellular fibronectin assembly in vitro. We found that the impaired migration and adhesion of VHL-null endothelial cells can be partially rescued by the addition of back exogenous fibronectin, which indicates that pVHL regulation of fibronectin deposition plays an important functional role in vascular patterning and maintenance of vascular integrity. (+info)
Persistent omphalomesenteric duct causing small bowel obstruction in an adult.
An extremely rare case of persistent omphalomesenteric duct causing small bowel obstruction is presented. A 20-year-old female patient without medical history presented with colicky abdominal pain, vomiting, absence of passage of gas and feces, and abdominal distension of 24 h duration. Physical examination and blood tests were normal. Abdominal X-ray showed small bowel obstruction. Computed tomography of the abdomen demonstrated dilated small bowel and a band originating from the umbilicus and continuing between the small bowel loops; an omphalomesenteric duct remnant was suspected. In exploratory laparotomy, persistent omphalomesenteric duct causing small bowel obstruction was identified and resected. The patient had an uneventful recovery and was discharged on the 5(th) postoperative day. Although persistent omphalomesenteric duct is an extremely infrequent cause of small bowel obstruction in adult patients, it should be taken into consideration in patients without any previous surgical history. (+info)
Antenatal sonographic features of aneurysmal dilatation of a vitelline vein.
We report a case of aneurysmal dilatation of a vitelline vein observed antenatally. Intra-abdominal vascular dilatation was diagnosed on ultrasound examination at 24 weeks' gestation. The relationship with the umbilicus and portal vein suggested the diagnosis of umbilical vein varix. Fetal tolerance remained excellent in spite of a gradual increase in the size of the dilated vein. Postnatal ultrasound examination revealed thrombosis of the aneurysm with gradual extension to the portal vein and the onset of serious coagulation problems. Operative findings on postnatal day 9 included the absence of intra-abdominal umbilical vein, and the presence of an abnormal, dilated and thrombosed vein connecting the umbilicus to the portal vein and following the trajectory of the right vitelline vein. Corrective surgery was attempted by resection of the aneurysm and portal thrombectomy, but this did not prevent the development of portal obstruction syndrome with cavernous hemangioma. This anomaly, in which the fetal venous return uses the vitelline vein in the absence of the umbilical vein, does not appear to have been described before. The mechanism in question could be anastomosis between the right vitelline vein and umbilical vein. Antenatal diagnosis should enable early surgical management before the formation of a portal thrombosis. (+info)