MOUSE MUSCLE CELL DIFFERENTIATION IN CLONAL CULTURE

Clonal culture of muscle cells from thigh muscles of the term fetus of the mouse was undertaken. Myoblasts were spherical or spindle-shaped, and proliferated exponentially until day 4 in culture. The generation time of the muscle cells from 2 to 4 days' culture was 9.1 to 13.4 hr. The fusion of myoblasts began on day 4 in culture; many myotubes had been formed by day 6 and spontaneous contraction was observed on day 7. Clonal efficiency was 30%, and the proportion of muscle colonies in all the colonies was 72%.     

EFFECTS OF THE LENS CAPSULE ON CELLULAR FLATTENING, CELL GROWTH AND EXPRESSION OF THE DIFFERENTIATED TRAITS OF CHONDROCYTES CULTURED IN VITRO

The morphology, growth and differentiation of chondrocytes cultured on the lens capsule were studied. When incubated in Eagle's MEM with fetal serum, chondrocytes on the surface of the lens capsule became flattened with extended pseudopodia, but most cell remained spherical on the surface of a plastic dish. Thus, the lens capsule promoted cellular flattening of chondrocytes. When grown in Ham's FI2 medium, flattening of cells on the lens capsule was greater and the cells developed the features of fibroblasts without any detectable characteristics of chondrocytes, although their growth rate was not enhanced. This inhibitory effect of the lens capsule on differentiation in this medium was reversed when the cells were separated from the lens capsule and grown on a plastic substrate.     

A Comparison Between Melanotic and Amelanotic Retinal Pigment Epithelial Cells In Vitro Concerning the Effects of L-Dopa and Oxygen on Cell Cycle

Melanin precursors and free radicals, cytotoxic substances, are produced during melanin synthesis by tyrosinase. We compared these cytotoxic effects of L-dopa and oxygen on the cell cycle of melanotic retinal pigment epithelial (RPE) cells with amelanotic RPE cells because of the differences of tyrosinase activities between melanotic and amelanotic RPE cells. Flow cytometric DNA analysis of RPE cells exposed to L-dopa (100 μM and 250 μM) were conducted at several oxygen concentrations (20%, 10%, and 5%). The dose-dependent effect of L-dopa to arrest the cell cycle (the S phase) was more pronounced in melanotic than in amelanotic RPE cells, and oxygen caused arrest in the G₁ phase.     

Demonstration of Transdifferentiation of Neural Retina from Pigmented Retina in Culture1

The formation of neural retina (NR) from retinal pigmented epithelium (RPE) of chick embryos in culture was investigated. In cultures of explants of PRE, depigmented, preretinal foci, consisting of 50 to 100 cells appeared in the pigmented central portion of the explant within three days. Then these depigmented cells increased rapidly in number and by about day 14 they formed characteristic spherical bodies, which were identified as a neural retinal-like structure (NR structure) by electron microscopic observations. Culture of explants of RPE from embryos of different stages showed that the capacity of embryonic RPE to form an NR structure decreased steadily with embryonic age from st. 24 to 27. At and after stage 27, no foci leading to the neural retinal differentiation were formed in the explants. Medium conditioned by cell cultures of chicken embryonic NR, RPE or chondrocytes had no effect on the formation of NR structures by explants of RPE.     

ACQUISITION OF COMPETENCE FOR CULMINATION DURING FINGER FORMATION IN DICTYOSTELIUM DISCOIDEUM

Finger-like structures of the cellular slime mold, Dictyostelium discoideum , were disrupted with a fine needle and the resulting cell masses were allowed to develop. When complete fingers formed under overhead lighting were disrupted, the cell masses rapidly became transformed into fruiting bodies. Development of similar cell masses from fingers reared in the dark was affected by the lighting conditions after disruption: under overhead lighting the cell masses rapidly culminated; under unilateral lighting, they formed fingers again and then migrating slugs.
In contrast, the cell masses from mounds with tips formed fingers regardless of the lighting conditions.
It is concluded from these findings that the cells become competent for culmination during finger formation under overhead lighting.     

Measurements of locomotor activity in hatchlings of the migratory locust Locusta migratoria: effects of intrinsic and extrinsic factors

Abstract. The effects of intrinsic and extrinsic factors on locomotor activity in crowd‐reared first‐stadium nymphs of the migratory locust Locusta migratoria are investigated under continuous light conditions using an actograph apparatus. Nymphs show monomodal or bimodal patterns of locomotor activity with respect to the time after the start of measurements, depending on the age. Locomotor activity is suppressed by the presence of grass in nymphs aged 0–2 days old but a peak of activity observed shortly after hatching is not suppressed. The results suggest that newly‐hatched nymphs may try to disperse from the hatching site. Nymphs show higher locomotor activity levels under moist conditions than under dry conditions during the first 5‐h period of measurements. This enhanced locomotor activity may constitute attempts to avoid high humidity. Under dim‐light conditions (2 × 10^?2 Wm^?2), locomotor activity is suppressed during the first half day and increases to a high level thereafter in both grass‐fed and unfed individuals. This increased activity might indicate a possible involvement of circadian rhythms. Background colour has no significant effect on the locomotor activity. The present study provides new aspects of behaviour in nymphs as well as baseline data for behavioural analysis of locust locomotion in relation to phase polyphenism.     

MITOTIC ACTIVITY OF VAGINAL EPITHELIAL CELLS FOLLOWING NEONATAL INJECTIONS OF DIFFERENT DOSES OF ESTROGEN IN MICE

In C57Black/Tw mice given injections of 1 μg estradiol-17β (E) for 5 days beginning on the day of birth, and killed a few days after the treatment, the vaginal epithelium showed estrogen-dependent proliferation and parakeratosis. In contrast, in the mice treated neonatally with 30 μg E for 5 days, the vaginal epithelium exhibited estrogen-independent proliferation and cornification or parakeratosis. Two peaks occurred in the mitotic rate in vaginal epithelial cells in the proximal and middle vaginae of the 1 μgE-treated mice, at 1 and 5 days of age, respectively, while the first peak was lacking in the distal vagina. The mitotic activity in 1 μgE-treated mice declined to the control level at 60 days. In the 30 μgE-treated animals also, 2 peaks were found in the mitotic rate at 1 and 7 days in both the proximal and middle vaginae. In contrast to the 1 μgE-treated mice, although the rate dropped once at 10 days, it increased again at 20 days and remained high thereafter. The second peak at 7 days of age coincided with the active proliferation of nodules appearing in the 30 μgE-treated mice. In the distal vagina, a peak occurred in the mitotic rate at 7 days without a preceding peak like that observed in the other parts of the vagina following the first injection of E on the day of birth.     

Response to nigh interruption in photoperiodic determination of wing form of the ground cricket Dianemobius fascipes

ABSTRACT. In the ground cricket Dianemobius fascipes (Walker), the occurrence of long- or short-winged form is determined by photoperiod during larval development. The pattern of this response is similar to that of diapause induction in other insects with a clearly defined critical nightlength (11.5 h). In symmetric skeleton regimes formed by a pair of 1 h light pulses, the critical nightlength is about 2 h longer than in the complete photoperiod. The long-night (short-wing) effect is eliminated by an interrupting light pulse. This response to night interruption shows only one peak in scotophases of various lengths and can be related to the critical nightlength before or after interruption. The light-reaction time required for the interruption effect changes during the night. In the early scotophase, 1 h of light is enough but 15 min fails to reverse the long-night effect, while a light pulse of only 1 min is effective about 1 h before the critical nightlength is reached. Several possible interpretations of this change are discussed.