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At least 883 records · Page 49Linked to original sources
PubMed1985

Histone messenger RNA synthesis and accumulation during early development in the echiuroid worm, Urechis caupo.

RNA isolated from Urechis caupo mature oocytes and embryos was analyzed for the presence of histone messenger RNAs (mRNAs) by in vitro translation and by filter blot hybridization to determine the contribution of maternal and newly transcribed histone mRNAs to the pattern of histone synthesis during early development. Histone mRNAs were not detected in mature oocyte RNA which suggests that relatively few if any maternal histone mRNAs are sequestered in the mature oocytes. Histone mRNAs were detected in cleavage-stage RNA and increased in amount from midcleavage through late gastrula stages. The in vitro translation analysis also demonstrated that the amount of H1 histone mRNA in late cleavage- and early blastula-stage embryos exceeds that of the individual core histone mRNAs. The disproportionate accumulation of individual histone mRNAs correlates with the noncoordinate synthesis of H1 and core histones which occurs during early embryogenesis.

Animals↗
PubMed1985

Developmental significance of a cortical cytoskeletal domain in Chaetopterus eggs.

The cortex of Chaetopterus eggs contains a cytoskeletal domain (CD) which includes a specific class of dense granular organelles and a large proportion of the maternal mRNA. This CD, along with its constituent dense granular organelles and mRNA, can be displaced to atypical locations in the egg by centrifugation. To investigate the developmental significance of the CD, we have examined the early development of egg and zygote fragments, prepared by centrifugation, which contained the CD, the nucleus, or both. Specifically, we prepared nucleate egg and zygote fragments depleted in the CD, and two-cell embryos in which the CD was present in only one cell. Nucleate centripetal egg fragments were both unable to develop after fertilization and were depleted in the CD, as shown by electron microscopy, acridine orange staining of cortical organelles, and hybridization with poly(U) and cloned DNA probes. In contrast, about 20-35% of the nucleate centripetal fragments derived from one-cell zygotes developed into swimming larva. Correlated with this improved success of development, we found that these zygotic centripetal fragments contained significant levels of the CD, using the same methods listed above. More effective removal of the CD from zygotic centripetal fragments by stratification prior to fragmentation virtually eliminated their ability to develop. The CD and associated components could be displaced into only one of the first two blastomeres by centrifugation of zygotes immediately prior to the first cleavage. Embryos containing the CD in only one blastomere continued to cleave, but formed defective larva. The results suggest that the cortical CD is necessary for normal embryonic development.

Animals↗
PubMed1986

Morphological identification of sperm receptors above egg microvilli in the polychaete, Neanthes japonica.

A fine-structural study of sperm-egg interactions in the polychaete Neanthes japonica was carried out. Unfertilized eggs are surrounded by a chorion 0.6-0.7 micrometers thick. Oocyte microvilli are inserted into the inner layer of the chorion. The outer layers of the chorion are opened just above the tips of the microvilli, where a membrane vesicle (microvillus tip vesicle, about 0.2 micrometers in diameter) plugs the chorion's opening. During fertilization, the acrosomal process of the sperm fuses with an egg microvillus within 1 min of insemination. All the microvillus tip vesicles disappear from the chorion surface within 5 min of insemination. When eggs, which are prefixed with glutaraldehyde, are inseminated, numerous sperm undergoing the acrosome reactions attach to the eggs. In the majority of these sperm, the tip of acrosomal process which is coated with the acrosomal content, adhere to a microvillus tip vesicle. These findings suggest that the microvillus tip vesicle serves as a sperm receptor, which induces the acrosome reactions and adhere to the sperm acrosomal process. The adhesion of the acrosomal process to the microvillus tip vesicle seems to be a prerequisite event for its fusion with the microvillus.

Animals↗
PubMed1991

Peptides from sperm acrosomal protein that initiate egg development.

How sperm initiate egg development is being investigated with gametes of the marine worm Urechis. Sperm acrosomal protein, previously shown to activate eggs (Gould et al., 1986, Dev. Biol. 117, 306-318; Gould and Stephano, 1987, Science 235, 1654-1656), was enzymatically cleaved into soluble peptide fragments. When this mixture was added to eggs they activated, and parthenogenetic cleavage often occurred. An active peptide (P23) was purified from the mixture and its sequence was determined to be Val-Ala-Lys-Lys-Pro-Lys. Synthetic peptide had the same biological activity. P23 induced eggs to undergo the complete sequence of changes that normally follows fertilization, including the fertilization potential, completion of meiosis, and DNA replication. When a sperm centrosome was introduced into eggs by prefertilization without activation, and the eggs were subsequently activated by P23, they developed normally to trochophore larvae (the contribution of another sperm component is not ruled out by this experiment). P23 covalently coupled to bovine serum albumin also activated eggs, showing that it acted on the external surface of the egg. The peptide did not activate sea urchin eggs, but did cause oyster eggs to undergo germinal vesicle breakdown.

Acrosome↗