A CpG-rich RNA and an RNA helicase tightly associated with the DNA demethylation complex are present mainly in dividing chick embryo cells.

In the developing chicken embryo, active DNA demethylation requires both RNA and proteins (Nucleic Acids Res. 25, 2375-2380, 1997; ibid. 25, 4545-4550, 1997, FEBS Lett. 449, 251-254, 1999a). In vitro assays indicate that in the 5- and 12-day-old embryos the highest specific activity of 5-methylcytosine DNA glycosylase is found in the brain, the eyes and the skin. In situ hybridization with antisense CpG-rich RNA tightly associated to the DNA demethylation complex shows a restricted expression pattern only in proliferating tissues such as the neuroepithelia of the brain in 5-day-old embryos. The RNA is absent in differentiated tissues like the skeletal and heart muscle, liver and the crystallin-producing cells in the lens. The CpG-rich RNA is transcribed in a developmental stage-specific rather than in a cell-specific manner. In contrast transcripts of DNA methyltransferase are found in dividing and quiescent cells. In situ hybridization with a probe of a RNA helicase which is also associated with the DNA demethylation complex shows a very similar localization in mitotically active tissues as the CpG-rich RNA. The content of 5-methylcytosine in individual cells was determined with a specific monoclonal antibody and cytometric analysis on tissue sections. The results indicate that proliferating cells have on the average 15% more methylated cytosines than non-dividing cells. This represents roughly 3x10(6) more methylation sites per haploid genome.

Implantation of a tissue-binding material in the female genital tract: a preliminary study on oviduct occlusion and the prevention of adhesions in baboons.

Studies conducted in adult female baboons have documented the potential usefulness of a new alloplastic substance, Proplast, when applied to the genital tract of the human female. Two areas of likely application are in the prevention of adhesions in infertility surgery and in reversible or permanent tubal occlusion.

Soft porous PTFE-composite alloplasts: tissue-bonding characteristics.

Experimental and clinical investigations over the past three decades have validated numerous hypotheses about tissue bonding of prostheses. Highly porous PTFE composite has been demonstrated to be an effective, inert, scaffold-like matrix onto which other materials can become physically bonded to achieve a tissue-specific result. Hydrophilic agents such as carbon and aluminum oxide stimulate ingrowth of fibroblasts that secrete collagen. These additives promote a robust and durable alloplast-soft tissue union composed mostly of collagen that is watertight. Bone-growth stimulants-such as hydroxyapatite-when added to highly porous PTFE stimulate tissue ingrowth and maturation that is more bone like.

Proplast leader for use in cruciate ligament reconstruction.

A synthetic leader has been used in 18 cases of medial one-third patellar tendon substitution for the anterior cruciate ligament and in 10 cases of posterior cruciate substitution using the medial head of the gastrocnemius tendon. The device adds length and facilitates manipulation of the transplanted tissues. There have been no problems with biocompatibility and there have been no instances of staple loosening or disruption of the junction between the stabilizer and transplanted tissues. Early results with the anterior cruciate substitutions suggest thet anchoring the transfer in bony tunnels in both the tibia and femur does not allow sufficient flexibility to prevent stretching or disruption of the tendon transfer.

Proplast tracheal prosthesis: a preliminary report.

Proplast, a recently developed biologically acceptable synthetic polymer has been utilized in replacement of the cervical tracheas of five dogs. The results of this initial study are encouraging and, in the opinion of the authors, justify further experimentation with this refined prosthetic model.