Paraffin Compression Due to the Rotary Microtome

The extent of compression of microtome sections has been studied for blocks with tissue and also blocks of clear paraffin. Thick sections are commonly compressed 15% or more, while in sections below 5 or 10 μ, compression may exceed 50%. Compensatory thickening of sections occurs. The degree of compression for various paraffin samples and for various conditions of knife edge, temperature, etc., is compared. Microscopical work, particularly where quantitative data or reconstructions are involved, is often seriously unpaired by unrecognized artifacts of sectioning. The present work indicates the magnitude of such artifacts. Compensation for distortions of sections is not easy because tissues, particularly dense tissues, may compress less than the paraffin matrix. Section corrugation is due to this inequality in compression. Absorption of water in section flattening causes some tissue readjustment, but this varies with different tissues and different fixations.     

Differential expression and genetic variation of hepatic messenger RNAs from genetically lean and fat chickens

Although excessive adiposity has become a major drawback in meat type chicken production, few of the genes involved in this process have been characterized so far. In order to identify putative genes involved in adiposity, we performed differential display analysis of RNAs extracted from the liver of divergently selected lean and fat chickens. Twenty-six differential products were selected and purified by single strand conformation polymorphism gel electrophoresis before sequencing and Northern blot analyses. An orthologous sequence of a mammalian cytochrome P450 2C subfamily member was proven to be differentially expressed in the liver of lean and fat chickens and could play an important role in the regulation of adiposity. In mammals, these genes are involved in detoxification of xenobiotics and metabolism of some important biological compounds. Four other genes were found differentially expressed to a lower extent. Some unidentified products were shown to be lean or fat specific, with sequence polymorphism and liver specific expression, strongly suggesting that the related gene could be directly involved in adiposity. Our data indicate that differential display can evidence genes with differential expression and with sequence polymorphism, making this strategy more accurate for differential analysis of messenger RNAs.