W. Mike Howell

Abnormal Expression of Secondary Sex Characters in a Population of Mosquitofish, Gambusia affinis holbrooki: Evidence for Environmentally-induced Masculinization

Paper mill effluents are discharged into Elevenmile Creek at Cantonment, Escambia County, Florida. The total population of mosquitofish, Gambusia affinis holbrooki, inhabiting the stream below the effluent discharge exhibits abnormal sexuality. All females are strongly masculinized, displaying both physical secondary sex characters and reproductive behavior of males. Males exhibit precocious development of physical secondary sex characters and reproductive behavior. Elevenmile Cr. above the paper-mill effluent, as well as tributaries to this creek, all contain Gambusia with normal secondary sex characters. This evidence strongly suggests that some yet unidentified chemical or combination of chemicals associated with the paper-mill effluent exerts a strong androgenic effect upon this population. This constitutes the first report of possible environmentally-induced masculinization involving a total natural population of vertebrates.

Visualization of ribosomal gene activity: Silver stains proteins associated with rRNA transcribed from oocyte chromosomes

Cricket oocyte chromosomes were stained with silver at pachytene when certain chromosome regions are active in rDNA amplification and rRNA transcription. The silver preferentially stained the known locations of 18S + 28S ribosomal cistrons. Cytochemical tests revealed that the silver binds neither to the rDNA nor transcribed rRNA, but rather to proteins which rapidly associate with the freshly-transcribed rRNA. As rRNA transcription proceeds, the quantity of silver stainable proteins progressively increases. The silver procedure can be used to visualize gene activity at the rDNA sites with conventional light microscopy.

Chromosome core structure revealed by silver staining

Chromosomes were subjected to either prolonged hypotonic solution pretreatment or aging. Both conditions greatly loosened and dispersed the overlying epichrormatin from the central chromosome core structure. This was followed by silver staining and examination with bright-field microscopy. The chromosome core selectively reduced the silver and stained black while the surrounding epichrormatin stained yellow. A single core was seen extending the length of each chromatid. Nucleolus organizer regions appeared to be attached to the core, while kinetochores seemed to be specialized regions of the core itself. Cytochemical tests indicated that the core component(s) responsible for silver staining was non-histone protein(s).

Gonopodial morphogenesis in female mosquitofish,Gambusia affinis affinis, masculinized by exposure to degradation products from plant sterols

SynopsisFemale mosquitofish,Gambusia affinis affinis, were masculinized by exposure to degradation products (presumably steroids) of the plant sterol, stigmastanol. Masculinization was indicated by the induction of a male-like gonopodium in each specimen. The morphogenetic stages of gonopodial development are discussed as are the anatomical specializations produced in the mature gonopodial tip.

A rapid technique for producing silver-stained nucleolus organizer regions and trypsin-giemsa bands on human chromosomes.

SummaryA simple and rapid technique is described whereby the nucleolus organizer regions (NORs) of human chromosomes can be differentially stained with silver. This staining is followed by trypsin-Giemsa banding on the same metaphase chromosomes. The metaphases simultaneously exhibit silverstained NORs and G bands, allowing for the unequivocal identification of all chromosomes and greatly facilitating studies involving the NOR-bearing acrocentrics.

Visualization of centriole-bodies using silver stain

Duplicate staining of human metaphase chromosomes, first with Giemsa followed by silver, revealed the presence of two small silver-stained bodies not seen in the Giemsa stained metaphases. Similar bodies were subsequently found in the metaphases of several animal groups. The size, structure, spatial relationships to the nucleus, behavior throughout the cell cycle, and apparent universal presence of these bodies suggest that they are either centrioles or associated centriolar structures. These centriole-bodies can be seen throughout the cell cycle, even in hypotonically spread C-metaphase chromosome plates. The silver stain procedure allows enough resolution to distinguish parent and daughter centriole-bodies at interphase, thus permitting visualization of the replication, maturation and separation stages of these bodies with the light microscope.

Silver stain reveals nucleolus organizer regions on a satellited Yq chromosome.

SummaryChromosomes from a patient with a satellited Yq were stained with a silver procedure that differentially stains nucleolus organizer regions. The Yqs stained heavily in all cells examined, indicating the presence of ribosomal cistrons at this region. The Yqs also entered into satellite associations with the D and G group chromosomes at a frequency greater than would be expected through chance.