Evolutionary Origin and Molecular Biology of the Melanoma-Inducing Oncogene of Xiphophorus

Melanoma formation in platyfish/swordtail hybrids of genus Xiphophorus is due to overexpression of the receptor tyrosine kinase oncogene Xmrk. This gene is the molecular equivalent to the Tu-locus of platyfish, formerly identified by Mendelian genetics. The supposed evolutionary origin of the Xmrk oncogene is a nonhomologous recombination event in the 5’region of the corresponding Xmrk protooncogene with an anonymous sequence, D. This event led to a gene duplication of Xmrk, whereby the new copy obtained a novel promoter derived from D. Inactivity of this promoter in parental fish warrants lack of tumorigenicity of the Xmrk oncogene in wild playfish. In hybrids, however, the promoter is active. This leads to the pigment cell transforming overexpression of Xmrk.     

Respiratory and Carbohydrate Changes in Developing Pea (Pisum sativum L.) Seeds in Relation to their Ability to Withstand Desiccation

In the development of garden pea seeds (P. sativum L., cv. ‘KelvedonWonder’) the ability to withstand desiccation was foundto be preceded by a fall in respiration rate and seed moisturecontent, both of which followed a sharp decline in ethanol-solublesugars. When harvested seeds were kept in high humidity conditionsrespiration was found to decline even though the moisture contentwas maintained. The fall in respiration was always associatedwith a fall in the level of sugars. Further experiments showedthat the seeds whose respiration had fallen in humid storagecould be induced to respire more rapidly by the addition ofsucrose. It is suggested that seeds can only withstand rapid desiccationafter a decrease in physiological activity following a fallin the supply of respiratory substrate in the form of sugars.     

Substrates Determine Spatial Distribution of Oxytricha bifaria (Ciliata Hypotrichida)

The extent to which a particular substrate (scratched glass) affects the distribution of a population ( Oxytricha bifaria ) that settled on it was measured, yielding the following results: (1) the species distinguishes among substrates slightly differing in the quality of their superficial scratches (average dimensions of 2, 2.8, 3.5, 6.5, 17 and 25 μm, respectively); (2) it "chooses" the preferred substrate by adopting specific differential behaviors; and (3) population cell density conditions its overall distribution.