Effects of Exogenous Thyroxine on Statolith Synthesis and Resorption in Aurelia

Aurelia ephyrae which were maintained in thyroxine during theirmetamorphosis from the polyp state and another group of ephyraewhich were in thyroxine forfour and eight days of starvation,had significantly reduced numbers of statoliths as comparedwith control ephyrae in equimolar concentrations of iodine andin artificial sea water. We conclude, therefore, that thyroxinesignificantly affects the mineralization and demineralizationof statocytes resulting in changes in statolith numbers. A mineralization role of thyroxine in other invertebrates hasnot been reported in spite of the fact that thyroxine and itsprecursors, monoiodotyrosine and diiodotyrosine, have been locatedin numerous invertebrates, particularly in mineralizing areassuch as developing shells. On the other hand, an important roleof thyroxine in mineralization and demineralization of bonesand teeth of vertebrates including humans, has been known forsome time. The specific role of thyroxine in affecting mineralizationin vertebrates is not known, due perhaps to the presence ofmany other hormones and second messengers which also affectmineralization. The use of the relatively simple Aurelia statolithtest systems and the exploration for other invertebrate mineralizingsystems which respond to thyroxine will hopefully lead to abetter understanding of the basic mechanisms of thyroxine actionin mineralizing systems in the future.     

Gymnodinium chukwanii n. sp. and Other Marine Dinoflagellates Collected in the Vicinity of Zanzibar

Thirty-five species of marine dinoflagellates are described and figured, including one new species, Gymnodinium chukwanii . These were collected by the author during the period February - March 1956. G. chukwanii has affinities to G. splendens and G. nelsoni and their group. The remainder of the paper is concerned with described species.     

The incidence of sweet potato virus disease and virus resistance of sweet potato grown in Uganda

Sweet potato virus disease (SPVD) was common (25–30% average incidences), and farmers recognised it as an important disease, in sweet potato crops in southern Mpigi, Masaka and Rakai Districts in Uganda, but SPVD was rare in Soroti and Tororo Districts. Whiteflies, which are the vector of sweet potato chlorotic stunt crinivirus (SPCSV) a component cause of SPVD, were correspondingly common on sweet potato crops in Mpigi and rare on crops in Tororo. However, aphids, which are the vectors of sweet potato feathery mottle potyvirus (SPFMV), the other component cause of SPVD, were not found colonising sweet potato crops, and itinerant alate aphids may be the means of transmission. Different sweet potato cultivars were predominant in the different districts surveyed and four local cultivars obtained from Kanoni in S. Mpigi, where whiteflies and SPVD were common, were more resistant to SPVD than four cultivars from Busia in Tororo District, where whiteflies and SPVD were rare. However, nationally released cultivars were even more resistant than the local cultivars from Kanoni. Yield results and interviews with farmers indicated that farmers in S. Mpigi were making compromises in their choice of cultivars to grow, some key factors being SPVD susceptibility, and the yield, taste, and marketability, duration of harvest and in-ground storability of the storage roots. These compromises need to be included in an assessment of yield losses attributable to SPVD.     

Archaebacterial Relationships of the Phosphoenolpyruvate Carboxykinase Gene Reveal Mosaicism of Giardia intestinalis Core Metabolism

A gene encoding a putative GTP-specific phosphoenolpyruvate carboxykinase has been cloned and sequenced from the type I amitochondriate protist Giardia intestinalis. The deduced amino acid sequence is related most closely to homologs from hyperthermophilic archaebacteria and only more distantly to homologs from Eubacteria and Metazoa. Most enzymes of Giardia core metabolism, however, are related more closely to eubacterial and metazoan homologs. An archaebacterial relationship has been noted previously for the unusual acetyl-CoA synthetase (ADP-forming) of this organism. The results suggest that phosphoenolpyruvate carboxykinase and acetyl-CoA synthetase have been acquired from different sources than most enzymes of Giardia core metabolism.     

Time-Lapse Filming of Cellular Interactions within Living Tissues

By a further development of the technique for time-lapse filming of organ cultures, it has become possible to observe the internal structure of the living tissues and to study the dynamics of intercellular contacts within the tissue. This method has been applied to a study of the interaction between the tissues of the chick chorioallantoic membrane and non-malignant fibroblasts, polyoma virus-transformed fibroblasts, and Harding-Passey melanoma cells. The behaviour of these cells in the absence and in the presence of colcemid has been investigated. From these studies it is concluded that disturbances in cell shape brought about by colcemid do not affect the invasive properties whereas the surface polypodial activity shown by the malignant cells is a major factor in tumour invasion.     

Mammalian Conception, Sev Differentiation, and Hermaphroditism as Viewed in Historical Perspective

This paper surveys in broad perspective some of the steps inthe development of theones of mammalian sex differentiationfrom antiquity to the present. The questions of why and howmales and females differentnte and why there are intersexeshave been answered by conjectures, speculations, and theones.In antiquity, when the existence of mimimhan egg and sperm wasunknownsex determination was con]ec tuicd to depend upon such factorsas which testis contiibuted the semen or which sideof the uterusreceived it. These fanciful notions peisisted until the middleof the 18th centuiy. Discovery of mammalian sperm in the samecentury and the ovum in the 10th centuiy led to obseivationsof fertilization. With advances in genetics andthe identificationot sex chromosomes, the 20th century was prepared to constructtheories foi normal sev differentiation and inteisexuality basedon experimental observation. The bovine freemartin—a naturalexperiment—prompted the hounonal theory leseaich on frogsled to a coittco medullaiy inductor theory, cellular cmmerismin fteemaitin and co tvun was the basis for a cellular theory.Of these, the hormonal theory in particular, provided some verifiablespeculations. However, there is no completely acceptable theoryand new lines of research are badly needed     

Thyroxine in Early Strobilation in Aurelia aurita

Radiochromatographic studies of ¹³¹I-treated Aurelia polypsrevealed synthesis of three compounds tentatively identifiedas monoiodotyrosine (MIT), diiodotyrosine (DIT), and thyroxine(T₄). One compound, MIT, is found within 8 hr after ¹³¹I administration,before the detection of DIT or T₄ which appear within 24 hr.T₄ is not usually detected after 48 hr although MIT and DITwere found up to the segmentation period. None of the compoundswere detected in ephyrae treated with ¹³¹I for 24 hr. Administration of low dosages of the goitrogens, thiourea,,propylthiouracil, and potassium thiocyanate, in conjunctionwith iodide, prevented strobilation induction. Radiochromatographyof jellyfish given the goitrogens and ¹³¹I revealed a reduceduptake of iodide and an impairment of the synthesis of the iodinatedcompounds. Jellyfish use thyroxine directly for strobilatioa inductionas demonstrated by ¹³¹I - labeled T₄ administration. The T₄was detected in the polyps up to the 48-hr period of strobilationduring which time some of the T₄ was excreted into the medium,as was some ¹³¹I. The fact that T₄, synthesis has thus far been found only instrobilating forms of Aurelia suggests that T₄ is involved primarilywith the differentiation of new structures which occurs duringstrobilation.