Dissecting the role of N-myc in development using a single targeting vector to generate a series of alleles.

The N-myc proto-oncogene is expressed in many organs of the mouse embryo, suggesting that it has multiple functions. A null mutation leads to mid-gestation lethality [1-4], obscuring the later roles of the gene in organogenesis. We have generated a multi-purpose gene alteration by combining the potential for homologous and site-specific recombination in a single targeting vector, and using the selectable marker for neomycin-resistance, neo, to downregulate gene activity. This allowed us to create a series of alleles that led to different levels of N-myc expression. The phenotypes revealed a spectrum of developmental problems. The hypomorphic allele produced can be repaired in situ by Cre-recombinase-mediated DNA excision. We show here for the first time the use of a single targeting vector to generate an allelic series. This, and the possibility of subsequent lineage-specific or conditional allele repair in situ, represent new genome modification strategies that can be used to investigate multiple functions of a single gene.

[CO2-laser surgery of rhinophyma]. / A rhinophyma CO2-laserrel végzett mütéte.

Authors are the first in Hungary to report on a CO2-laser dermabration performed for the treatment of rhinophyma. They describe the mode and results of the laser intervention justifying the application of the CO2-laser.

[Radial forearm and fibula free flap reconstruction after radical resection of head and neck malignancies] / Alkari és fibula értengelyû szabadlebenyek alkalmazásával végzett tapasztalataink a fej-nyaki régióban.

The incidence of head and neck cancer has been rapidly increasing in Hungary during the last decade. Most of these tumors are discovered in advanced stage, consequently, surgical removal of the tumor results in large complex defects in the soft tisses and bone elements of the face and neck. For optimal anatomical and functional reconstruction we perform free flap transfer in increasing number of cases. Between December 1993 and March 2001 in the Head and Neck Surgery Department of the National Institute of Oncology the defects after resection of head and neck tumors were reconstructed with free flaps in 85 cases. Radial forearm flap in 64 cases, fibula osteoseptocutaneous flap in 14 cases were used. In 87% of the patients the postoperative period was uneventful, the surgical complications were not more numerous than following traditional reconstructions. The average duration of operations became shorter by 2.5 hours during the last two years than before. In most of the cases we achieved good functional and esthetic results. The quality of life of the patients was excellent in 14%, almost normal in 73% and bad with serious problems of social life in 13%. It is surprising that there was no significant difference between the survival of neck node positive and negative patients. In our practice the replacement of large defects in the head and neck region with free flaps is a reliable and useful method for reconstruction.

Embryonic stem cells alone are able to support fetal development in the mouse.

The developmental potential of embryonic stem (ES) cells versus 3.5 day inner cell mass (ICM) was compared after aggregation with normal diploid embryos and with developmentally compromised tetraploid embryos. ES cells were capable of colonizing somatic tissues in diploid aggregation chimeras but less efficiently than ICMs of the same genotype. When ICM in equilibrium with tetraploid and ES in equilibrium with tetraploid chimeras were made, the newborns were almost all completely ICM- or ES-derived, as judged by GPI isozyme analysis, but tetraploid cells were found in the yolk sac endoderm and trophectoderm lineage. Investigation of ES contribution in 13.5 day ES in equilibrium with tetraploid chimeras by DNA in situ hybridization confirmed the complete tetraploid origin of the placenta (except the fetal blood and blood vessels) and the yolk sac endoderm. However, the yolk sac mesoderm, amnion and fetus contained only ES-derived cells. ES-derived newborns failed to survive after birth, although they had normal birthweight and anatomically they appeared normal. This phenomenon remains unexplained at the moment. The present results prove that ES cells are able to support complete fetal development, resulting in ES-derived newborns, and suggest a useful route for studying the development of genetically manipulated ES cells in all fetal lineages.