Document Type

Dissertation

Date of Award

1977

Keywords

Small Intestine, Mice, Anatomy, Stem cells

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Sciences

First Advisor

Stuart O. Landry, Jr.

Second Advisor

John Christian

Third Advisor

Judy D. Hall

Abstract

Location and Morphology of Paneth Cells

Paneth cells (Figs. 1 and 15) are conspicuous cells found at the base of the intestinal crypts, throughout the length of the small intestine, in mammals. They were first discovered by Schwalbe (1872) and extensively described by Paneth (1888). These cells contain large (1-3 u) spherical, acidophilic granules. As seen with the light microscope (LM), Paneth cells have basal basophilia (an indication of ribosomes), a basally located, often deeply indented nucleus, a supranuclear Golgi apparatus, and secretory granules in the supranuclear region and apical cytoplasm.

Paneth Cell Ultrastructure

The Paneth cell secretory granules of rats (Erlandsen and Chase 1972 a and b) and men (Trier 1963, Erlandsen et al, 1974), like those of the exocrine pancreatic cells (Jamieson 1972), are always homogeneously electron dense. However, those of mice, Mus musculus, are heterogeneous, being composed of a basic, electron dense protein core (Selzman and Liebelt 1961), presumed to be lysozyme (Spicer et al, 1967, Geyer 1973, Otto 1973), and of an electron lucent cortex that, in section, appears as a halo around the protein core (Hally 1958) (e.g. Fig. 11).

This halo is composed of acid glycosaminoglycan (Selzman and Liebelt 1961, Geyer 1966, Spicer et al, 1967, Schirrmeister et al 1972). Some sugar moieties in the secretory granule are to be expected, for in many cell types, proteins for cell export, or membrane proteins that span the entire trilaminar plasma membrane, usually contain sugar moieties, while those that are used within the cell or that are in the cytoplasmic leaflet of the plasmalemma, usually do not (Jakoi et al 1976).

Fine electron dense lines of unknown function and composition are visible in the halo. In mature secretory granules, these lines seem to radiate from the core (Fig. 12). At other times, they seem to form a network in the halo (Fig. 5). Some hints on the significance of these lines may be obtained from consideration of more intensively studied secretory cells.

Although such lines are not visible in zymogen granules of the pancreatic exocrine cells, Rothmans group (S. Rothman 1971, Burwen and S. Rothman 1972, S. Rothman et al 1974) reports that pancreatic enzymes are attached to specific sites on large molecules that are themselves attached to the inner surface of the secretory granule membrane and that are arranged centripetally from the granule membrane to the granule center. Such an arrangement allows a great concentration of the secretory product in granules within the cell by rendering the secretory granule impervious to the osmotic effects of the watery cytoplasm in which it is located. The function of the condensing vesicle thus becomes one of arranging the secretory product, as well as simply removing fluid from the vesicle. This theory of the orderly arrangement of secretory product within the pancreatic zymogen granule is compatible with the morphology of the mouse Paneth cell secretory granule.

Condensing vesicles in the Golgi area of mouse Paneth cells are often polar (Fig. 2, Fig. 15, PC3), one half electron translucent, the other half electron dense. In sections, these condensing vesicles may look like half moons (Hally 1958) (Fig. 5).

The nucleus of a Paneth cell is often deeply notched, the number of indentations increasing with the age of the cell (Cheng 1974). The luminal surface of a Paneth cell has a few short microvilli (Fig. 16) but microvilli are absent just above a secretory granule that is about to be released.

The lateral and basal plasmalemma is relatively smooth and there is a basement membrane. The basement membrane is probably similar to that of embryonic salivary gland, containing a glycosaminoglycan complex (Cohn et al 1977). In the salivary gland, the basement membrane is responsible for maintaining the lobular morphology of the acinus (Banerjee et al, 1977).

There is abundant rough endoplasmic reticulum at the base of the mouse Paneth cell. Protein for cell export is synthesized on the ribosomes of the rough endoplasmic reticulum and moves to the Golgi apparatus (Fig. 2 and Fig. 15, PC3), then via transitional vesicles (Fig. 5) to a condensing vesicle that matures into the typical secretory granule. The secretory granule moves to the cell apex, the luminal pole, and remains there until it is discharged (Trier et al, 1966).

In Paneth cells of fasted mice, the transit time for labeled amino acids to move from the rough endoplasmic reticulum to the cell apex was 6 to 8 hours (Trier et al, 1966). The rate of transit was increased in vivo, by a combination of feeding and pilocarpine stimulation (Trier et al, 1966, Linss 1967). In fed, pilocarpine stimulated mice, the transit time was 3 to 6 hours.

This polar morphology of basal rough endoplasmic reticulum and apical accumulation of storage forms of a cell product (the secretory granules) is typical of exocrine secretory cells. Because this polar morphology is discernable at the LM level as well as at the electron microscopic (EM) level, it has been known for a long time that Paneth cells are exocrine secretory cells (Schwalbe 1872, Paneth 1888, Hally 1958, Trier 1963, Moe 1968). However, their exact function has not been determined.

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