The influence of tissue polarity on nematocyte migration in Hydra attenuata

Influences underlying the direction of nematocyte migration in hydra were studied. Nematocytes arise by interstitial cell differentiation in the body column, and then up to 80% migrate into the ectodermal epithelial cells of the tentacles. The migration of these cells, which is clearly apically directed, may be due either to a chemotactic attraction into the hypostome and tentacles, or to a property inherent in the tissue of the body column, such as the regeneration polarity. To distinguish between these two possibilities, the rates of accumulation of ³H-proline-labeled desmoneme and stenotele nematocytes in unlabeled heads (hypostome and tentacles) grafted either basally or apically to the labeled body column were compared. Basally grafted heads, if left in place for an appropriate length of time, reversed the regeneration polarity of the tissue. In all experiments the direction of desmoneme migration was correlated with the direction (apical or basal) of the regeneration polarity of the tissue. Further, the kinetics of polarity reversal were modified by varying the grafting procedure or the environmental conditions. In every case the kinetics of reversal of desmoneme migration also paralleled the kinetics of reversal of tissue polarity. The results suggest that the direction of desmoneme migration is influenced by the regeneration polarity of the tissue. Stenotele migration was largely unaffected by tissue polarity, but behaved as though chemotactically attracted to the head.     

Oriented migration of interstitial cells and nematocytes inHydra attenuata

Summary The migratory properties of hydra cells within the tissue were studied. The extent and direction of cell migration were examined in budding, non-budding, and regenerating animals. Nematocytes and a small number of single big interstitial cells (the multipotent interstitial cells) actively migrate preferentially in an apical direction. Basal migration of these cells occurs only when a bud is present and, in which case, the cells migrate into the developing bud. The regeneration of the hypostome and tentacles does not affect cell migration in either direction, except for apical migration of stenotele nematocytes, which was markedly reduced.This research was supported by National Science Foundation Grant (GB 29284), National Institute of Health Grant (HD 08086-01), and N.I.H. Public Health Service Training Grant (HD 00347).     

Radioautographic studies of the initial site of formation of protein-bound iodine in the rat thyroid gland

1. Predominantly cellular labelling was observed in radioautographs of rat thyroid glands fixed by perfusion from the aorta at intervals between 5 and 55s after [(125)I]iodide administration via the aorta. 2. When perfusion was delayed for 2min, or if immersion fixation was used, the labelling was predominantly over the peripheral portion of the follicular lumen, in agreement with the observations of other investigators. 3. The findings support the concept that the initial site of binding of iodine to protein is intracellular, but the nature of this protein has not been established.     

The role of hormones and prostanoids in the in vitro proliferation and differentiation of human myoblasts

Fetal human myoblasts have been employed to examine the role of hormonal factors in human myogenesis. The results show that human myoblast proliferation is stimulated by insulin, hydrocortisone, and prostaglandin F2 alpha (PGF2 alpha). Exposure of human myoblasts preparing to differentiate to either PGE2 or isoproterenol results in the precocious initiation of differentiation (i.e., cell fusion and increase in creatine kinase activity). Three antagonists of prostanoid synthesis, indomethacin, aspirin, and DL-6-chloro-alpha-methylcarbozole-2-acetic acid, inhibit cell number increase with complete inhibitions of proliferation at 5 X 10(-5) M indomethacin and 6 X 10(-4) M aspirin. Reversal of the indomethacin-imposed block is achieved by prostaglandin F2 alpha. The same antagonists of prostanoid synthesis, when added to older cultures, depress prostaglandin E (PGE) levels and inhibit human myoblast differentiation. During differentiation, PGE is present in both the intracellular compartment (0.47 to 0.66 pmol/microgram DNA) and the culture medium (1.83 to 4.53 nmol PGE). The results suggest a role for prostanoids in the regulation of both human myoblast proliferation and differentiation. They also demonstrate that the active cyclooxygenase products are produced endogenously by the in vitro myogenic population. The findings are discussed within the context of what is known of the relationship between growth factor and prostanoid actions and the roles of these two categories of hormones in the regulation of myogenesis.     

Characteristics of the macrophage uptake of proteinase-α-macroglobulin complexes

Complexes formed between labelled proteolytic enzymes (trypsin, subtilopeptidase A) and the α-macroglobulins of plasma are rapidly and selectively taken up by rabbit alveolar macrophages. The uptake occurs oxver a narrow zone of pH. Kinetics of the uptake is affected by temperature; in particular, incubation of macrophages at 37° C before the addition of labeled complex reduces the capacity to take up complexes. EDTA prevents the association of labelled complexes with macrophages, and can dissociate previously bound label. The effect of EDTA is reversed by the addition of calcium or magnesium or both. Iodoacetamide does not prevent the uptale of complexes but causes them to remain available for dissociation from the cells by EDTA. Incubation of complexes with macrophages at 37° C with no iodoacetamide results in the appearance of trichloroacetic acid soluble products of the enzyme in the supernatant fluid. These observations indicate that the selective uptake of proteinase-α-macroglubin complexes with rabbit alveolar macrophages can be resolved into three phases: (1) membrane binding which depends upon divalent cations and is pH sensitive, (2) endocytosis inhibitable by iodoacetamide and (3) temperature-dependent hydrolysis of the contained labelled enzyme.