Search PubMed⌕ Search

Biomedical subjects

K C Sadler

Publications and source records attributed to K C Sadler.

6 recordsLinked to original sources
PubMed2001

Postmeiotic unfertilized starfish eggs die by apoptosis.

Fertilization of starfish eggs during meiosis results in rapid progression to embryogenesis as soon as meiosis II is completed. Unfertilized eggs complete meiosis and arrest in postmeiotic interphase for an, until now, indeterminate time. If they remain unfertilized, the mature postmeiotic eggs ultimately die. The aim of this study is to characterize the mechanism of death in postmeiotic unfertilized starfish eggs. We report that, in two species of starfish, in the absence of fertilization, postmeiotic interphase arrest persists for 16-20 h, after which time the cells synchronously and rapidly die. Dying eggs extrude membrane blebs, undergo cytoplasmic contraction and darkening, and fragment into vesicles in a manner reminiscent of apoptotic cells. The DNA of dying eggs is condensed, fragmented, and labeled by the TUNEL assay. Taken together, these data suggest that the default fate of postmeiotic starfish eggs, like their mammalian counterparts, is death by apoptosis. We further report that the onset and execution of apoptosis in this system is dependent on ongoing protein synthesis and is inhibited by a rise in intracellular Ca(2+), an essential component of the fertilization signaling pathway. We propose starfish eggs as a useful model to study developmentally regulated apoptosis.

Animals↗
PubMed2001

Starfish oocytes form intracellular ice at unusually high temperatures.

Starfish oocytes, eggs, and embryos are popular models for studying meiotic maturation, fertilization, and embryonic development. Their large (170- to 200-microm) oocytes are obtainable in copious amounts and are amenable to manipulations that mammalian oocytes are not. The most formidable obstacle to working with marine oocytes is their seasonal availability, yet a successful means of preserving them for use during the nonreproductive season has not been reported. The aim of this study was to investigate the response of starfish oocytes to freezing with rapid and slow cooling rates under a variety of conditions to develop a cryopreservation protocol for these cells. Cryomicroscopic observation revealed that starfish oocytes in isotonic medium undergo intracellular ice formation (IIF) at very high subzero temperatures, such that the mean difference between the temperature of extracellular ice formation (T(EIF)) and IIF (TI(IF)) was less than 3 degrees C and the average T(IIF) was approximately between -4 and -6 degrees C. Neither partial cellular dehydration nor addition of the cryopreservative dimethyl sulfoxide significantly depressed the T(IIF). Under some conditions, we observed ice nucleation at multiple locations within the cytoplasm, suggesting that several factors contribute to the unusually high T(IIF) during controlled-rate freezing and thus vitrification may be a more suitable method for cryopreserving these cells.

Animals↗
PubMed1998

Components of the signaling pathway linking the 1-methyladenine receptor to MPF activation and maturation in starfish oocytes.

Starfish oocytes are arrested at the G2/M-phase border of meiosis I. Exposure to their natural mitogen, 1-methyladenine (1-MA), leads to the activation of MPF and MAP kinase, resumption of the meiotic cell cycle, and fertilization competency. The 1-MA receptor has not yet been identified, but it is known to be linked functionally to a pertussis toxin-sensitive G-protein. G beta gamma appears to be the major effector of the 1-MA receptor, since injection of G beta gamma, but not activated G alpha i, leads to the activation of MPF, entry into meiosis, and oocyte maturation. The components that connect G beta gamma to MPF and MAP kinase activation in oocytes are unknown. In mammalian cells, a novel phosphatidylinositol 3-kinase, PI-3 kinase-gamma, links G beta gamma to the MAP kinase activation pathway. Here we show that PI-3 kinase is required for starfish oocyte maturation. LY294002 and wortmannin, inhibitors of PI-3 kinase, block MPF and MAP kinase activation and entry into meiosis. Inhibition by LY294002 is reversible and limited to the hormone-dependent period. Neither inhibitor, however, blocks the earliest hormone-induced event, formation of actin spikes at the cell membrane. By contrast, pertussis toxin blocks both actin spiking and later events, arguing that PI-3 kinase functions downstream of G beta gamma. Finally, we show that unlike the well-studied case in Xenopus oocytes, where MAP kinase is an essential component of the MPF activation pathway, MAP kinase is not required for either MPF activation or subsequent oocyte maturation in starfish. Instead, its major role appears to be suppression of DNA synthesis in unfertilized, haploid eggs.

Animals↗
PubMed1992

Localization of xenopsin and xenopsin precursor fragment immunoreactivities in the skin and gastrointestinal tract of Xenopus laevis.

Xenopsin (Xp) and xenopsin precursor fragment (XPF) are bioactive peptides derived from a single precursor molecule; both were isolated previously from extracts of Xenopus laevis skin. The present immunohistochemical study was undertaken to determine the specific cellular localization of these two peptides in the skin and also in the gastrointestinal tract of adult Xenopus. We report here that Xp-like and XPF-like immunoreactivities co-exist in the granular glands of the skin and specific granular cells in the lower esophagus and stomach. However, only Xp-like immunoreactivity, not XPF-like immunoreactivity, was detected in tall, thin cells of the duodenum and in club-shaped cells of the large intestine. The immunochemical co-localization of the two peptides in specific cells of the skin, lower esophagus and stomach suggests that the same gene is expressed in each of these cells, and that the precursor molecule undergoes similar post-translational processing. In contrast, the observation that certain cells of the duodenum and large intestine display only one peptide immunoreactivity suggests an alternative phenomenon, possibly involving selective peptide accumulation or expression of a different gene.

Amino Acid Sequence↗
PubMed1975

Composition of cottontail rabbit milk from stomachs of young and directly from gland.

Milk samples were from stomachs of 27 nursing cottontail rabbits (Sylvilagus floridanus) within 5 min after cessation of nursing. Four milk samples were directly from mammary glands by hand milking aided by tranquilizer and oxytocin. Means and standard errors for 27 stomach samples for total solids, fat, protein, lactose, and ash were 33.6 +/- .8%, 13.9 +/- 1.7%, 14.6 +/- .5%, 2.22 +/- .05%, and 2.06 +/- .07%. Those values of 4 samples directly from the gland were 35.2 +/- .4%, 14.4 +/- .4%, 15.8 +/- .6%, 2.67 +/- .26%, and 2.07 +/- .06%. Fatty acid compositions were similar for the groups, except linoleic acid was 30.0% of fatty acids from stomach milk and 24.7% in milk obtained directly. Differences between sampling methods in palmitoleate, stearate, and oleate may have been from differences in season of sampling. Minerals were more concentrated in milk obtained directly, except potassium. Differences between milks of domesticated and cottontail rabbits are discussed.

Animals↗