Susan Daniels-McQueen

In Vitro Colony Assay for a New Class of Megakaryocyte Precursor: Colony-Forming Unit Megakaryocyte (CFU-M)

Summary A plasma culture system has been used successfully to grow and quanti-tate megakaryocyte colonies from mouse bone marrow following their staining for acetylcholinesterase activity in situ. Colonies averaging about six acetylcholinester-ase-positive cells appear with a peak incidence after 4 days in culture with a plating efficiency of one colony formed for every 104 nucleated cells plated.

Specificity of the induction of ferritin synthesis by hemin

We have previously reported that hemin derepresses ferritin mRNA translation in vitro. As noted earlier, pre-incubation of a 90 kDa ferritin repressor protein (FRP) with hemin prevented subsequent repression of ferritin synthesis in a wheat germ extract. The significance of this observation has been investigated further. Evidence is presented here that this inactivation of FRP is temperature dependent. Neither FeCl3, Fe3+ chelated with EDTA, nor protoporphyrin IX caused significant inactivation of FRP under comparable conditions, whereas Zn2(+)-protoporphyrin IX produced an intermediate degree of inhibition. The presence of a glutathione redox buffer (GSB), which was previously shown to minimize non-specific side-effects of hemin, was not necessary for the derepression reaction. Inclusion of mannitol, a free radical scavenger, did not alter the inactivation caused by hemin. Calculation of the expected ratio of hemin monomers to dimers suggests that the active species is the monomer.

Isolation and Characterization of Human Cytotrophoblast Cells

One of the unique features of the placenta is its continued differentiation during gestation. We have previously shown by in situ hybridization, that human choriogonadotropin (hCG) α and β subunit mRNAs are expressed in both the cytotrophoblast and syncytiotrophoblast regions of the placenta whereas human placental lactogen (hPL) mRNA was expressed only in the syncytium. HCGα mRNA is reduced 6-fold between first trimester and term, and hCGβ mRNA falls to undetectable levels (Boothby et al., 1983). HPL, on the other hand, attains maximal levels at term although the amount of mRNA per gram of tissue is not greatly altered (Hoshina et al., 1982). Based on these data we proposed that the hormonal genes are activated at different stages of placental differentiation (Hoshina et al., 1982, 1983, 1985). We also suggested that hCG α and β subunit expression is dependent on the presence of proliferating cytotrophoblasts whereas hPL expression is sustained in differentiated syncytium.

Human Chorionic Gonadotropin Alpha and Beta Subunit mRNAs: Translatable Levels During Pregnancy and Molecular Cloning of DNA Sequences Complementary to hCG

One of the important functions of the human placenta is to produce peptide hormones during pregnancy. The major ones elaborated by the trophoblast are human chorionic gonadotropin (hCG) and human placental lactogen (hPL). The appearance of the hormones in maternal serum during pregnancy is quite different. Whereas hCG peaks in the first trimester, hPL reaches maximal levels near term. Since the levels of these hormones differ during the course of gestation, it is apparent that the factors controlling their synthesis are not the same. Thus the human placenta represents a convenient and unique tissue for studying expression of human hormonal genes during development.

Modular organization of the multipartite central pattern generator for turtle rostral scratch: knee-related interneurons during deletions

Central pattern generators (CPGs) are neuronal networks in the spinal cord that generate rhythmic patterns of motor activity in the absence of movement-related sensory feedback. For many vertebrate rhythmic behaviors, CPGs generate normal patterns of motor neuron activities as well as variations of the normal patterns, termed deletions, in which bursts in one or more motor nerves are absent from one or more cycles of the rhythm. Prior work with hip-extensor deletions during turtle rostral scratch supports hypotheses of hip-extensor interneurons in a hip-extensor module and of hip-flexor interneurons in a hip-flexor module. We present here single-unit interneuronal recording data that support hypotheses of knee-extensor interneurons in a knee-extensor module and of knee-flexor interneurons in a knee-flexor module. Members of knee-related modules are not members of hip-related modules and vice versa. These results in turtle provide experimental support at the single-unit interneuronal level for the organizational concept that the rostral-scratch CPG for the turtle hindlimb is multipartite, that is, composed of more than two modules. This work, when combined with experimental and computational work in other vertebrates, does not support the classical view that the vertebrate limb CPG is bipartite with only two modules, one controlling all the flexors of the limb and the other controlling all the extensors of the limb. Instead, these results support the general principle that spinal CPGs are multipartite.