Cyclin E and Its Associated cdk Activity Do Not Cycle during Early Embryogenesis of the Sea Urchin

Female sea urchins store their gametes as haploid eggs. The zygote enters S-phase 1 h after fertilization, initiating a series of cell cycles that lack gap phases. We have cloned cyclin E from the sea urchin Cyclin E is synthesized during oogenesis, is present in the germinal vesicle, and is released into the egg cytoplasm at oocyte maturation. Cyclin E synthesis is activated at fertilization, although there is no increase in cyclin E protein levels due to continuous turnover of the protein. Cyclin E protein levels decline in morula embryos, while cyclin E mRNA levels remain high. After the blastula stage, cyclin E mRNA and protein levels are very low, and cyclin E expression is predominant only in cells that are actively dividing. These include cells in the left coelomic pouch, which forms the adult rudiment in the embryo. The cyclin E present in the egg is complexed with a protein kinase. Activity of the cyclin E/cdk2 changes little during the initial cell cycles. In particular, cyclin E-cdk2 levels remain high during both S-phase and mitosis. Our results suggest that progression through the early embryonic cell cycles in the sea urchin does not require fluctuations in cyclin E kinase activity

The polyribosomal protein bound to the 3' end of histone mRNA can function in histone pre-mRNA processing.

Cell cycle-regulated histone mRNAs end in a conserved 26-nt sequence that can form a stem-loop with a six-base stem and a four-base loop. The 3' end of histone mRNA has distinct functions in the nucleus and in the cytoplasm. In the nucleus it functions in pre-mRNA processing and transport, whereas in the cytoplasm it functions in translation and regulation of histone mRNA stability. The stem-loop binding protein (SLBP), present in both nuclei and polyribosomes, is likely the trans-acting factor that binds to the 3' end of mature histone mRNA and mediates its function. A nuclear extract that efficiently processes histone pre-mRNA was prepared from mouse myeloma cells. The factor(s) that bind to the 3' end of histone mRNA can be depleted from this extract using a biotinylated oligonucleotide containing the conserved stem-loop sequence. Using this depleted extract which is deficient in histone pre-mRNA processing, we show that SLBP found in polyribosomes can restore processing, suggesting that SLBP associates with histone pre-mRNA in the nucleus, participates in processing, and then accompanies the mature mRNA to the cytoplasm

Determination of Cytokine Protein Levels in Cervical Mucus Samples from Young Women by a Multiplex Immunoassay Method and Assessment of Correlates▿

Cytokines in cervical mucus are likely to play important roles in controlling pathogens. The cervical mucosal environment is complex, however, with many endogenous and exogenous factors that may affect cytokine levels. We used a multiplex, suspension-array-based immunoassay method to measure 10 proinflammatory (interleukin-1β [IL-1β], IL-6, and IL-8) and immunoregulatory (gamma interferon [IFN-γ], IL-2, IL-4, IL-5, IL-10, IL-12, and IL-13) cytokines in cervical mucus specimens collected via ophthalmic sponge from 72 healthy, nonpregnant women and correlate their levels with biologic and behavioral covariates in a cross-sectional design. Proinflammatory and immunoregulatory cytokines were readily detected, although proinflammatory cytokines were present at markedly higher levels than were immunoregulatory cytokines. Among the covariates examined, the most striking finding was the significant (P ≤ 0.05) association between depressed levels of the cytokines IFN-γ, IL-1β, IL-6, and IL-10 and cigarette smoking. Also, nonsignificant trends toward lower cytokine levels were found in the settings of incident and persistent human papillomavirus infection. The ready detection of proinflammatory cytokines may be reflective of the female genital tract as an anatomic site that is constantly exposed to immunogenic stimulation. Cigarette smoking appears to downregulate cytokine responses in the cervical mucosa, which may help explain the implicated role of tobacco use as a cofactor for cervical cancer development

Cyclin D and cdk4 Are Required for Normal Development beyond the Blastula Stage in Sea Urchin Embryos

cdk4 mRNA and protein are constitutively expressed in sea urchin eggs and throughout embryonic development. In contrast, cyclin D mRNA is barely detectable in eggs and early embryos, when the cell cycles consist of alternating S and M phases. Cyclin D mRNA increases dramatically in embryos at the early blastula stage and remains at a constant level throughout embryogenesis. An increase in cdk4 kinase activity occurs concomitantly with the increase in cyclin D mRNA. Ectopic expression of cyclin D mRNA in eggs arrests development before the 16-cell stage and causes eventual embryonic death, suggesting that activation of cyclin D/cdk4 in cleavage cell cycles is lethal to the embryo. In contrast, blocking cyclin D or cdk4 expression with morpholino antisense oligonucleotides results in normal development of early gastrula-stage embryos but abnormal, asymmetric larvae. These results suggest that in sea urchins, cyclin D and cdk4 are required for normal development and perhaps the patterning of the developing embryo, but may not be directly involved in regulating entry into the cell cycle

The sea urchin stem–loop-binding protein: a maternally expressed protein that probably functions in expression of multiple classes of histone mRNA

Following the completion of oogenesis and oocyte maturation, histone mRNAs are synthesized and stored in the sea urchin egg pronucleus. Histone mRNAs are the only mRNAs that are not polyadenylated but instead end in a stem–loop which has been conserved in evolution. The 3′ end binds the stem–loop-binding protein (SLBP), and SLBP is required for histone pre-mRNA processing as well as translation of the histone mRNAs. A cDNA encoding a 59 kDa sea urchin SLBP (suSLBP) has been cloned from an oocyte cDNA library. The suSLBP contains an RNA-binding domain that is similar to the RNA-binding domain found in SLBPs from other species, although there is no similarity between the rest of the suSLBP and other SLBPs. The suSLBP is present at constant levels in eggs and for the first 12 h of development. The levels of suSLBP then decline and remain at a low level for the rest of embryogenesis. The suSLBP is concentrated in the egg pronucleus and is released from the nucleus only when cells enter the first mitosis. SuSLBP expressed by in vitro translation does not bind the stem–loop RNA, suggesting that suSLBP is modified to activate RNA binding in sea urchin embryos