Development of the structural components of the brush border in absorptive cells of the chick intestine

Abstract

The spatial and temporal relationships between cytoplasmic filaments and the morphogenesis of the intestinal brush border were examined by transmission electron microscopy of normally developing tissue and of tissue exposed to a variety of experimental conditions in organ culture. Distinct stages in the development of the brush border were identified: (1) Irregular projections of the apical plasma membrane that contain a network of microfilaments are converted to uniform projections filled with a core bundle of straight microfilaments (7-11d of incubation). (2) Rootlets form by an elongation or aggregation of filaments (11-15d). (3) The terminal web forms first as a network of short filaments just below the apical plasma membrane, then secondarily stratifies into two layers (19d of incubation to 3d posthatching). (4) Core filaments elongate as microvilli achieve their maturity (21d of incubation to 5d posthatching). Microvillus formation was not perturbed by culturing 9d tissue in high concentrations of Ca++ or Mg++, either with or without the ionophore, A23187. Rootlet formation was stimulated by high Mg++, with or without A23187, and, for reasons unknown, by ethanol. Terminal web formation was not stimulated by Mg++ or Ca++, but the integrity of the terminal web was lost when 21d embryonic tissue was cultured with EGTA or cytochalasin B. After stratification, the terminal web could not be disrupted by EGTA, but instead was aggregated to the center of the apical end of the cell.

Poultry viscera and bone meal in broiler pre-starter and starter diets

“…The authors suggested that the amount of digestible isoleucine in diets became insufficient when viscera meal in the diet was over 5%. El-Sheikh et al (1996) indicated that the supplementation of methionine and lysine to broiler diets containing viscera meal increased nitrogen use and performance. Alleman et al (2000) offered a plausible explanation for the reduced performance.…”

“…Likewise, the inclusion of animal byproducts reduced digestion and absorption of fats, which can be justified by the lower inclusion of soybean oil in diets. Besides, on the first posthatch days, chicks are not completely mature to digest and absorb nutrients, especially fat (Chambers & Gray, 1979;Moran Jr., 1994;Krogdahl & Sell, 1989).…”

The cytoskeleton in development of epithelial cell polarity

“…Early research on BB cytoskeleton formation focused on embryonic chickens, mice and rats (Chambers and Grey, 1979;Ezzell et al, 1989;Maunoury et al, 1988;Rochette and Haffen, 1987;Shibayama et al, 1987;Stidwill and Burgess, 1986;Takemura et al, 1988), with subsequent work utilizing cell lines (Dudouet et al, 1987;Peterson et al, 1992). Recently, attention has turned to understanding the development of the BB in adult tissues.…”

Mechanical transformations of living cavitary bodies

“…Microvilli, similarly to pollen tubes or fungal hyphae, look like regular cylinders with a dome-shaped apex (see electron micrographs: Mooseker and Tilney, 1975;Chambers and Grey, 1979;Hirokawa et al, 1982). Filopodia may also look like this (see Bridgman and Dailey, 1989, Fig.…”

“…There are numerous indications that the arrangement of actin filaments is not strict in cell outgrowths. For instance, while the central filaments in mature microvilli are arranged in longitudinal bundles, at the early stage of the outgrowths' development they usually form an unstructured network (Chambers and Grey, 1979;Tilney and Jaffe, 1981). Bundles of filaments were absent both in thin processes (Savion and Selinger, 1978) and in lamellar evaginations (Andrews, 1976).…”