Apical Invaginations Research Articles

The fine structure of the renopericardial cavity of the cephalopod Octopus dofleini martini

The renopericardial cavity of Octopus dofleini martini has been studied with the electron microscope. The renopericardial cavity, which appears as a rudimentary coelom, is lined with a single layered epithelium and is separated from the surrounding connective tissue by a basal lamina. The epithelium, ∼45 μ m in thickness, is composed of two different cell types: (1) a conspicuous, ciliated and cylindrical cell type, characterized by apical, lateral and basal membranous invaginations; and (2) a comparatively small cell type, the “lacuna forming” cell, which is in contact with the basal lamina. The coelomic origin of other parts of the excretory organs in Octopus is discussed.

The early development of the cement apparatus in the barnacle, Balanus balanoides (L.) (Crustacea: Cirripedia)

The development of the cement cells of Balanus balanoides (L.) has been followed over a 26-day post-settlement period. Cells of the cyprid cement glands de-differentiate to form part of the juvenile barnacle apparatus, but the majority of juvenile cement cells develop by differentiation of collecting duct cells. These latter cement cells are recognized by apical invaginations which are continuous with the collecting duct lumen. Collecting ducts are present in the cyprid. The cement duct system was not studied in detail, but preliminary observations of the arrangement in B. balanoides and Elminius modestus Darwin have shown them to differ, the system in E. modestus being simpler.

Some observations on the fine structure of the human mesonephros.

The mesonephros from human embryos ranging 7-20mm in total length was investigated with light and electron microscopes. The fine structure of the mesonephric glomerulus is characterized by a thick endothelium, wide subendothelial space and poorly differentiated podocytes. These features which are prominent in the 7-12mm embryos are obscure in the glomerulus of larger embryos which are rather similar in fine structure to that of the metanephros.The proximal tubule of the mesonephros consists of columnar cells bearing long microvilli and apical invaginations and vesicles suggesting pinocytotic activity. The distal tubule consists of tall columnar cells with smooth apical surfaces doming into the lumen and lacks the basal infoldings.In the subendothelial space of the mesonephric glomerulus there are found fine filaments approximately 100Å in diameter extending from the glomerular basement membrane toward the endothelium. After treatment with ruthenium red, their diameter increases to 200Å. The glomerular basement membrane strongly reacts to ruthenium red. There are many granules approximately 100-200mμ in diameter in the basal part of the podocytes. These granules and fine filaments are supposed to participate in the formation of the glomerular basement membrane.Mesangial cells are found in the intercapillary space surrounded by a basement membrane and at the vascular pole accompanied by capillaries. A juxta-glomerular apparatus cannot be found.

An electron microscopical study of absorbing cells in the posterior caput epididymidis of rabbits

The columnar cells in regions 3 and 4 of the ductus epididymidis in rabbits display ultrastructural features characteristic of absorbing cells. The stereocilia show basal anastomoses and often a fibrillar core continuous with a fibrillar web in the apical cytoplasm. Numerous invaginations of the slightly “downy” apical cell membrane and many thick-walled apical vesicles and vacuoles contain an opaque substance similar to that seen in the lumen. The vacuoles often contain small vesicles or bodies, probably formed from the vacuolar wall by budding. Numerous bodies or vacuoles with moderately dense contents are seen in the Golgi area and in the supranuclear and intranuclear cytoplasm in region 3. In region 4 they are denser and mainly seen above the nucleus. A high acid phosphatase activity was demonstrated in most dense and some light bodies. India ink introduced by way of the rete testis was taken up from the lumen into apical invaginations, vesicles and vacuoles and slowly transferred to denser bodies below the Golgi apparatus. These observations are interpreted as evidence for a resorption of substances from the lumen by a pinocytotic process, and for their storage and perhaps digestion in the dense bodies, which appear to have a lysosomal character. The Golgi apparatus is large with many vesicles of two types and empty cisternae but few typical Golgi vacuoles. The partly granular endoplasmic reticulum is very well developed and has opaque contents. Microtubules run from the terminal bar region into the Golgi area. Thick-walled vesicles occur throughout the cytoplasm, sometimes in continuity with the cell membrane. The basal parts of the cell borders often interdigitate.