The development of the early 2‐cell mouse embryo to the late 2‐cell stage is marked by the appearance between 23 and 26 h post‐insemination of a complex of polypeptides of mol. wt. approximately 67 K. Addition of alpha‐amanitin between 18 and 21 h post‐insemination prevents or reduces the subsequent appearance of these polypeptides. Addition of alpha‐amanitin after 21 h does not obviously affect the appearance of the approximately 67 K polypeptides. A major change in synthetic profile occurs between 29 and 32 h post‐insemination involving many polypeptides. Addition of alpha‐amanitin to 2‐cell embryos prior to 29 h post‐insemination prevents the appearance of the new polypeptides observed during this major change but does not prevent the disappearance of the old polypeptides. In contrast, addition of alpha‐amanitin after this time does not affect the appearance of the new polypeptides. This result, together with other evidence presented, suggests that during the 2‐cell stage the embryonic genome shows transcriptional activity in two phases at 18‐21 and 26‐29 h post‐insemination, that these transcripts are utilized soon after their synthesis, and that most maternal transcripts used before the second phase of embryonic transcription become ineffective soon afterwards.

Supplemental Digital Content is Available in the Text. Adding multicolumn spinal cord stimulation to optimal medical management improved pain relief, health-related quality of life, and function in a traditionally difficult to treat population of failed back surgery syndrome patients with predominant low back pain.

Summary The formation of a mouse blastocyst involves the use of genetic information derived from the expression both of maternal genes in the preovulatory oocyte and of embryonic genes from the mid‐2‐cell stage onwards. Evidence is reviewed suggesting that maternal RNA transcripts made up to 20 days prior to ovulation are available for use after fertilization, that no significant KNA synthesis occurs between germinal vesicle breakdown and the mid‐2‐cell stage and that during this interval of transcriptional inactivity production of protein is regulated at a post‐transcriptional level. Embryonic genes first become active at the mid‐2‐cell stage and at, or shortly after, this time most maternal mRNA is inactivated. Thereafter, the available evidence suggests that although embryonic mRNA has considerable stability, much of it is translated immediately after it is transcribed. This tight linkage of mRNA transcription and utilization appears to be crucial for certain key events in development. The cellular interactions operating during early development are described. It is suggested that asymmetry of cell contacts in the 8‐cell embryo imparts a mosaic structure to the embryo, and that this mosaicism is conserved and elaborated with division to the 16‐ and 32‐cell stages. The mechanisms are discussed by which mosaicism is induced and through which the two cell lineages of the blastocyst are founded. Temporal events in preimplantation development show a periodicity of about 27 h. It is proposed that within each period differentiative events are cumulative but reversible, and that the boundaries between each developmental period constitute points of commitment at which reversal of development becomes no longer possible.

Premature rupture of membranes is more common in pregnancies occurring in women with systemic lupus erythematosus than in control pregnancies. Disease activity, prednisone use, and serologic studies are not predictive. Premature rupture of membranes is the major etiology of preterm birth in this cohort.