Structure and function of the spermatheca in a snail host of schistosomiasis, Biomphalaria glabrata

The histochemistry and ultrastructure (SEM and TEM) of the spermatheca of Biomphalaria glabrata was investigated to elucidate the function of this organ and to compare its structure and function to similar organs found in other species. The spermatheca has a debris-filled lumen surrounded by a thin wall of tissue. The cells adjacent to the lumen are of three columnar epithelial cell types. Two cell types have abundant microvilli and mammalian cell-like organelle distribution and morphology. The above cell types differ in the electron density of their cytoplasms, nuclear morphologies, and organelle content. The third cell type differs from the other two in its cytoplasmic makeup. However, the most distinctive difference is the presence of large numbers of cilia at the apical surface with no evidence of microvilli. These columnar cells rest on a basal lamina adjacent to a two to three cell thick muscle layer. The entire organ is surrounded by an adventitia of unusual morphology. Histochemical investigation demonstrated that DNAase, RNAase, and protease are present in the lumen, alkaline phosphatase is associated primarily with the microvilli, small amounts of acid phosphatase are concentrated in the midcell area of the columnar epithelium, and ATPase activity is localized in the muscle cells and just below the absorptive surface of the microvillous cells. The luminal contents and adventitial areas are Sudan Black B positive, all areas of the lumen and organ wall are PAS positive, the cell nuclei and amorphous masses in the lumen showed Feulgen staining, and large vesicles in the columnar cells were Oil Red O positive. Apparently, the spermatheca of B. glabrata is both a digestive and absorptive structure. Although this organ shares functional similarities with those found in opisthobranchs and terrestrial pulmonates, the epithelia of the spermatheca differ dramatically in these groups.     

The snail (Biomphalaria glabrata) genome project

In 2001, ideas for a snail genome project were discussed at the American Society of Parasitologists meeting (New Mexico) and a snail genome consortium was subsequently established (the first consortium meeting was held in 2005). A proposal for sequencing the snail genome was submitted to the National Human Genome Research Institute, and Biomphalaria glabrata was prioritized as a non-mammalian sequencing target in 2004. The sequencing of the genome of this medically important snail is now underway.     

The food-finding orientation mechanism of Biomphalaria glabrata (Say)

An experimental procedure involving the use of time-lapse cinematography for accurately recording pathways was used to investigate the responses of Biomphalaria glabrata (Say) to a stimulus source of plant chemicals. This allows a more detailed analysis of the orientation mechanism than is the case with the Y-maze method. Snails of this species, which are essentially herbivorous, respond either by klinotaxis or tropotaxis or both to a source of plant chemicals. It was not possible to demonstrate the involvement of kinesis in the orientation mechanism.     

The ultrastructure of secretion in the spermatheca of the salamander, Manculus quadrigitatus (Holbrook)

Spermathecae of mature salamanders (Manculus quadridigitatus) were studied by light and electron microscopy. Gross morphology exhibits a complex of muscle, connective tissue and pigment cells surrounding a cluster of tubules, which empty into a ciliated central duct leading to the cloacal cavity. The tubules are composed of myoepithetial cells and secretory cells, anchored to an encompassing basal lamina. Secretion products appear to be initiated as crystalline deposits, seen in mitochondrial repositories, which are subsequently sequestered in the perinuclear region. Observations show these vesicles to be precursors of the Golgi synthesis of carboxylated polysaccharides, as determined by histochemical tests using toluidine blue, ruthenium red, and alcian blue. The secretory products are emptied into the tubule lumen. thereby bathing the stored sperm and maintaining them in a viable state for approximately 8 months. The storage tubules appear to be a complete complex of varying epithelial cells specifically designed to support viable sperm and to resorb non-functional forms.     

The role of the osphradium in chemoreception by the snail Biomphalaria glabrata (Say)

The possible involvement of the osphradium of Biomphalaria glabrata (Say) in food finding has been investigated by using behavioural assays to determine whether snails with cauterized osphradial canals can locate a source of food extract in still water. A new technique for anaesthetizing the snails for the cautery experiments is described. The experimental results indicate that a functional osphradium is not essential for directional movement towards a source of food extract. The present results are in conflict with those of Michelson (1960). Reasons for the differences between the present results and those of Michelson and the possible functional roles of the osphradium are discussed.     

The chemical ecology of Biomphalaria glabrata (say): Sugars as phagostimulants

• 1.1. The buccal-mass responses of the freshwater snail Biomphalaria glabrata to sugars were investigated by means of an olfactometer.
• 2.2. The snails proved very discriminating in their responses. Adults responded significantly to only five (12.2%) of the 41 sugars tested at 10⁻² M. Juvenile conspecifics had a broader niche as they responded to eight (47%) of the 17 sugars tested.
• 3.3. Of all the sugars tested, maltose proved to be the most potent phagostimulant.
• 4.4. The possible mechanisms involved in the chemoreception of active sugars and the ecological relevance of the responses shown by the snails to them are discussed.

     

Role of the visceral nerve in heart rate variations during different behavioral patterns in Megalobulimus sanctipauli (mollusca,gastropoda, pulmonata)

• 1.1. The role of the visceral nerve in mediating the changes in heart rate associated with different behavioral patterns was investigated in Megalobulimus sanctipauli.
• 2.2. The results of acute and chronic denervation experiments indicate that the visceral nerve has no excitatory or inhibitory tonic action on the heart of snails retracted into the shell, nor does it account for the increase in heart rate associated with the locomotion and feeding behaviors.
• 3.3. These changes in heart rate are, probably, indirect effects of increased activity such as an increase in venous return.
• 4.4. The visceral nerve is responsible for approximately 3/4 of the increase in heart rate associated with the first minute of extrusion.
• 5.5. The small increase in heart rate observed in denervated animals is probably caused by an increase in venous return generated by muscle activity that forces the head and food out of the shell.

     

The ultrastructure of the spermatheca in the red spotted newt

In continuing study of gene and genome interaction as a possible etiological mechanism in normal and abnormal growth and malformation, the ventral spinous processes (VSPs, crural insertions of the diaphragm) were used as additional epigenetic variants to portray differences in the basic gradient growth pattern. Over 700 comparisons of mean differences in number (range or magnitude) and peak (position) of the VSP gradient, in the same populations of strains III, DA, and III_Da (into which the Da gene had been introduced from strain DA), provided populations of +/+, Da/+ and Da/Da on two different genome backgrounds. They reveal the individual effects on the VSPs of underlying growth processes associated with the Da gene dosage, vertebral border shifts and stillbirths. Both Da and stillbirths demonstrate growth influences which interact additively to reduce the range and shift the peak anteriorly in opposition to those of the border shifts. The growth effects induced by border shifts are in some cases significantly so much greater as to seemingly inhibit or even reverse either the specific gene Da or stillbirth effects. The way that interaction of such growth influences can enhance, suppress or cancel each other and the relation to specific growth gradients and functions is of particular importance to understanding the etiology and growth mechanisms of spontaneous and unexpected exogenously or endogenously induced malformations in non-isogenic stocks.     

Establishment of the comet assay in the freshwater snail Biomphalaria glabrata (Say, 1818)

The single cell gel electrophoresis or the comet assay was established in the freshwater snail Biomphalaria glabrata. For detecting DNA damage in circulating hemocytes, adult snails were irradiated with single doses of 2.5, 5, 10 and 20 Gy of (60)Co gamma radiation. Genotoxic effect of ionizing radiation was detected at all doses as a dose-related increase in DNA migration. Comet assay in B. glabrata demonstrated to be a simple, fast and reliable tool in the evaluation of genotoxic effects of environmental mutagens.     

The significance of the amoebocyte-producing organ in Biomphalaria glabrata

In molluscs, internal defence against microorganisms is performed by a single cell type, i.e., the haemocyte or amoebocyte. The origin of these cells in Biomphalaria glabrata was initially thought to be localised within the vasculo-connective tissue. More recently, origin from a single organ, termed the amoebocyte-producing organ (APO), has been postulated based on the occurrence of hyperplasia and mitoses during Schistosoma mansoni infection. The present investigation represents a histological, immuno-histochemical and ultra-structural study of the B. glabrata APO, whereby histological identification was facilitated by means of collecting epithelial basophilic cells. These cells were comprised of single-cell layers that cover a portion of the stroma, which contains many small, round cells and haemolymph sinuses, as well as a small area of the pericardial surface of the reno-pericardial region. On occasion, this epithelial component vaguely resembled the vertebrate juxtaglomerular apparatus, which reinforces its presumed relationship to the kidney. Both in normal and infected molluscs, mitoses were only occasionally found. The present quantitative studies failed to demonstrate the presence of APO cellular hyperplasia, either in normal or schistosome-infected B. glabrata. Conversely, several structural details from the APO region in B. glabrata were found to be consistent with the hypothesis that the APO is a filtration organ, i.e., it is more closely related to the kidney rather than the bone marrow, as has been suggested in the literature.     

The galactan-degrading enzymes in the snail Biomphalaria glabrata.

1. Embryonic snails incorporate from the perivitelline fluid in which they are embedded a polysaccharide, called galactan, which is composed entirely of D-, or D- and L-galactose. In this investigation the p-nitrophenyl-beta-D-galactoside degrading enzyme of Biomphalaria glabrata which was assumed to be involved in the degradation of the galactans was purified almost to homogeneity and its specificity was studied. 2. It has a mol. wt of 135,000 and is composed of two identical subunits. 3. It could be shown that p-nitrophenyl-beta-D-fucoside was hydrolysed eight times faster, but native galactan was neither decomposed nor was it inhibitory for the hydrolysis of p-nitrophenyl-glycosides. 4. Thus, it is most likely that this galactosidase is not involved in the galactan metabolism. 5. However, a membrane-bound enzyme complex was revealed which was able to metabolize the native galactan of Biomphalaria glabrata completely and which showed graded reactivity towards galactans of other species. 6. Since no intermediate degradation products were found it must be assumed that they were metabolized further in the mitochondria.