Four-cell Embryos Research Articles

Development of mouse embryos with abnormalities induced by parental heat stress.

Summary. Albino ICR mice were used in a factorial experiment to study abnormal embryonic development that was induced by a 24-hr exposure of parent mice to an ambient temperature of 34·5° C and 65% relative humidity. Two-cell embryos recovered from eighty females killed at 48 hr were cultured in vitro to the stage reached 120 hr after HCG. The pattern of embryonic development in vivo was determined by observing embryos recovered from 240 females killed at 64, 72, 88 or 96 hr after HCG. Exposure of females caused an accumulation of two-, three- and four-cell embryos (P<0·01) following development in vivo or in vitro. Complete developmental arrest at the two-cell stage accounted for the major portion of embryonic mortality. In some partially affected two-cell embryos, one blastomere was able to undergo a limited number of divisions, asynchronous cleavage, to form three- or five-cell trophoblastic vesicles, or false blastocysts. Following exposure of males, developmental retardation and/or arrest at the morula stage accounted for a major portion of the embryonic death that had occurred by Day 10 of gestation. Significant male × female treatment interactions in the data on number of morulae, blastocysts and viable fetuses indicated that embryonic mortality due to male and female stress may be operating through similar mechanisms.

Viability and survival of mouse embryos following parental exposure to high temperature.

65% relative humidity for a period of 24 hr. The treatment of males commenced 48 hr before a 6-day mating schedule and of females, at 16.00 hours on the day a copulatory plug was detected. The females were killed 54 hr or 10 days after a plug had been detected. The developmental stages of embryos recovered at 54 hr were recorded and four-cell and eight-cell ova were incubated in [3H]uridine and subjected to autoradiography. Females killed at Day 10 of gestation gave estimates of pre- and postimplantation embryonic mortality. A significant increase in rectal temperatures (approximately 2\s=deg\C) following treatment was taken as indicating stress had occurred. Extensive developmental retardation and/or arrest among embryos recovered from stressed females at 54 hr resulted in an increase in the proportion of two-, three- and four-cell embryos. This retardation was coincident with fewer blastomeres of four-cell (P<0\m=.\01) and eight-cell embryos (P<0\m=.\05)being able to incorporate [3H]uridine in comparison to those from control females. After male stress, developmental retardation was evident as an accumulation (P<0\m=.\05) of four-cell embryos but only the eight-cell embryos exhibited a reduction (P<0\m=.\05) in the number able to incorporate [3H]uridine.

A cytological study of artificial parthenogenesis in the sea urchin Arbacia punctulata.

Eggs of the sea urchin Arbacia punctulata were artificially activated with hypertonic seawater. The artificially activated eggs undergo the cortical reaction which is not distinguished by a wavelike progression as in the case of inseminated eggs. The cortical granules are released at random loci at the surface of the egg and result in spaces separated by large cytoplasmic projections. Unreacted cortical granules and ribosomes are found within the matrix comprising the large cytoplasmic projections. No "fertilization cone" is formed. The subsequent release of additional cortical granules results in the formation of a continuous perivitelline space, 15 min following activation. 85 min postactivation, an organization of annulate lamellae, endoplasmic reticulum of the smooth variety, and microtubules around a centriole is observed prior to nuclear division. Before the breakdown of the nuclear envelope a streak stage is formed. The streak is composed of a central core of annulate lamellae and is encompassed by endoplasmic reticulum and vesicular components. Condensation of chromatin is followed by the establishment of the mitotic apparatus. Centrioles were not found in the mature egg; however, they are present after activation prior to the first nuclear division, in the four-cell embryo, multicellular embryo, and at blastula. Artificially activated eggs have been observed to develop to the pluteus stage in more than 50% of the eggs treated.

Messenger RNA in Early Sea-Urchin Embryos: Size Classes

Rapidly labeled RNA from four-cell embryos and blastulae of sea urchins was analyzed by sedimentation and for ability to form DNA-RNA hybrids. The RNA was derived from polyribosomes and from the "gel interphase," an extraction compartment resulting from treatment of whole embryos with phenol and known to be enriched with nuclei. The RNA from both sources displayed a high degree of structural complementarity to DNA. This DNA-like RNA of the polyribosomes sedimented in discrete classes, rather than in the sedimentation continuum demonstrable for the labeled RNA of the gel interphase. Thus messenger RNA appears to emerge in the cytoplasm in discrete size classes.