[Potential clinical applications of the sentinel node procedure in oral cancer]. / Toepassingen van de schildwachtklierprocedure bij mondholtecarcinomen.

In cases of oral cavity cancer a reliable diagnostic technique is needed to detect occult regional lymph node metastases and to avoid futile elective neck dissections as well as undertreatment. The first studies revealed a sensitivity of 94%. However, the sentinel node procedure is not yet a routinely performed procedure in oral cancer.

Mechanism of polar body formation in the mouse oocyte: an interaction between the chromosomes, the cytoskeleton and the plasma membrane.

The influence of mouse oocyte chromosomes on their immediate environment has been investigated following their dispersal by dissolution of the metaphase spindle with nocodazole. Small clusters of chromosomes become redistributed around the egg cortex in a microfilament-dependent process. Each cluster has the capacity, on removal from nocodazole, to organize a spindle that rotates to yield a polar body. In this process of spindle formation, the chromosome clusters are able both to promote tubulin polymerization in their vicinity and to recruit microtubule-organizing centres (MTOCs) which organize the polymerized tubulin into spindles. In addition each oocyte chromosome cluster, as well as the non-dispersed sperm-derived haploid group of chromosomes, induces a focal accumulation of subcortical actin (corresponding to a filamentous area devoid of organelles) and a loss of surface Concanavalin A binding activity (corresponding to a loss of surface microvilli) in the overlying cortex. This induction ceases with the formation of pronuclei whether or not the pronuclei migrate centrally. Pronuclear formation is sensitive to the action of nocodazole for up to 2-4 h postinsemination, and pronuclear migration is totally sensitive to the drug. If pronuclei are blocked in a peripheral location by nocodazole they are associated with an elevation in Con A binding activity of the overlying membrane which corresponds to an area of the surface rich in blebby microvilli.

Changes in actin distribution during fertilization of the mouse egg.

Unfertilized mouse oocytes and eggs 1-8 h after fertilization in vitro were examined at the light microscope level for structural changes, distribution of actin (as assessed by both antiactin antibodies and NBD-phallicidin), surface binding of concanavalin A (Con A) and chromosomal distribution and condensation. The influence of cytochalasin D on these events was also assessed. Changes in actin distribution were associated with rotation of the second anaphase spindle, formation of the second polar body, the events following incorporation of the sperm nucleus, and formation and migration of the pronuclei. Cytochalasin D prevented spindle rotation, polar body formation, pronuclear migration and the restoration of Con A binding over the site of sperm entry and the site of polar body formation, but did not affect sperm fusion and entry, the loss of Con A binding at the site of sperm entry and pronuclear formation.

The transition from maternal to embryonic control in the 2-cell mouse embryo.

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.

Post-transcriptional control in the early mouse embryo.

The earliest stages of mouse embryogenesis, from fertilisation to the two-cell stage, are characterised by an extremely low level of RNA synthesis. Indeed, during this period, RNA polymerase II activity and incorporation of labelled precurosrs into heterogeneous RNA are not detectable, and there is no increase in the poly(A) content of the embryo, but rather a slight decrease. The rate of protein synthesis remains low and relatively constant throughout the one- and two-cell stages. However, qualitative analysis of the protein synthetic profile on SDS gels has revealed changes which appear around the late one-cell to early two-cell stage. This early change in the pattern of polypeptide synthesis represents the first major qualitative molecular change found so far in development. We present evidence which suggests that the increased synthesis at the early two-cell stage of a small number of polypeptides of molecular weight 35,000 is not dependent on transcription, but rather represents control at a post-transcriptional level using mRNAs synthesised before fertilisation.