Early Morphogenesis of Chick Gonad in the Absence of Mesonephros

The development of the gonads in male and female chick embryos with induced unilateral mesonephric agenesis was studied using grafting, histoenzymology, and electron microscopy. As in embryos with a mesonephros, proliferation of the coelomic epithelium and its interaction with mesenchymal cells to form the medullary cords take place in the amesonephric gonads. In a similar manner, gonadal sexual differentiation and the differentiation of steroidogenic tissue, detectable by the presence of Δ5-3β-hydroxysteroid dehydrogenase, do not appear to be affected by the absence of an organized mesonephros. However, the initiation of gonadal development, further growth, and the onset of meiosis observable in developing ovaries are retarded. This delay appears to be reversible, as was demonstrated by experiments in which ovaries from chicks with complete mesonephric agenesis were transplanted into the coelomic cavity of male and female 3 1/2-day-old embryos. Meiosis finally occurred in the oocytes of all ovaries, regardless of the sex of the host. Therefore, the presence of a differentiated mesonephros in chick embryos is not required for the establishment of an undifferentiated gonad and sexual differentiation, or for initiation of meiosis.     

Selective Expression of PNA-Binding Glycoconjugates by Invasive Human Melanomas: A New Marker of Metastatic Potential

Alterations of cell-surface glycoconjugates have been associated with invasiveness and metastatic capacity in a number of experimental and human tumors (bladder and colon cancer). We have recently shown that human melanoma cells from variants selected for high metastatic potential in an animal model bind the lectin peanut agglutinin (PNA), and that human melanoma cell populations enriched for PNA binding cells generate a higher frequency of metastases when xenografted into immune suppressed neonatal rats. We have therefore sought cells binding PNA in biopsied human melanocytic tumors and compared frequencies of PNA binding by cells from benign nevi, early and late primary melanomas, and metastatic melanomas. Sections of conventionally processed tissues were deparaffinised and exposed to biotinylated PNA; PNA fixation was revealed by the avidine/peroxidase/AEC technique. In 51 specimens tested, PNA appears to react electively with invasive tumors, since only one of the 7 early primary melanomas (Clark III) reacted while 13/23 late primary melanomas (Clark III-V), and 4/21 melanoma metastases were reactive. In addition, only 1/17 benign nevi bound PNA. In primary tumors, the reactive cells were exclusively invasive tumors cells in the dermis. PNA reactive material was observed in the cytoplasm and plasma membrane of reactive cells. Hence, alterations in composition and cellular localisation of glycoconjugates detectable by lectin histochemistry in melanoma cells may be markers of metastatic potential that may be applicable on an individual patient basis.     

Does Aconitum septentrionale chemically protect floral rewards to the advantage of specialist bumblebees?

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