Role of Centriolar Matrix and Striated Rootlets in Centriolar Pairing and Orientation During Spermatogenesis in Hydractina echinata

Transmission electron microscopy of the spermatogenic stages of the hydroid, Hydractinia echinata, reveals a series of complex structural and positional changes in the centrioles of spermatocytes and spermatids. The newly generated centriolar pairs of spermatocytes form an unusual four-centriole aggregate that persists until cell division. The distal centrioles of this aggregate are shrouded with a very dense matrix that accumulates after centriolar replication. This matrix facilitates the mechanical attachment between distal centrioles and microtubular nucleating satellites, striated rootlets and pericentriolar processes. The association of these accessory structures occurs sequentially and is repeated in spermatocytes and spermatids. An electron dense plaque, which is an extension of distal centriolar matrix, is interposed between centriolar pairs of the aggregate. The plaque structurally maintains the centriolar aggregate and apparently facilitates the orientation of centrioles to prevent spacial interference while satellites, rootlets and pericentriolar processes associate with the distal centrioles. Striated rootlets are also involved in maintaining precise spacing and orientation between centriolar pairs. A single striated rootlet emanates from the base of each distal centriole of the aggregate and attaches with the opposite distal centriole. The attachment of rootlets to distal centrioles changes the spacing and orientation of centriolar pairs during the process of precocial flagellar development seen in Hydractinia spermatogenesis

Mathematics teachers' beliefs about teaching and learning mathematics and constraints influencing their teaching practice

In my doctoral work I studied three mathematics teachers in lower secondary school in Norway and how they interpreted a curriculum reform, L97 (Kleve, 2007). This was an ethnographic study which included methods as focus groups, conversations with teachers, teachers’ self estimations and classroom observations. In this paper I point out constraints influencing mathematics teachers’ teaching practice and discuss the relation between the three teachers’ beliefs about teaching and learning mathematics and their teaching practices relating to the research literature more widely. Finally I emphasise the importance of identifying such constraints

Isolation of Nuclei from Physarum flavicomum: Demonstration of Nuclear Cyclic Acid AMP Phosphodiesterase

Cyclic AMP phosphodiesterase activity in the nucleus of the myxomycete Physarum flavicomum was demonstrated by cytochemical staining utilizing electron microscopy and by enzymatic assays with tritiated cyclic AMP as the substrate. Cytochemical staining showed Physarum\u27s plasmodial phosphodiesterase activity to be located in the nucleus, along the plasma membrane, in vesicles, and free in the cytoplasm. Nuclear phosphodiesterase, which may be cell cycle dependent, was primarily located in the nucleolus. Nuclei from three to five day old microplasmodial cultures were isolated by the method of Henney and Yee. Whole cells were collected through centrifugation and washed. Pellets were homogenized in a medium composed of 0.01 MTris-HC1 (pH 7.2 at 4 °C), 0.25 M sucrose, 0.01% Triton X-100, and 5mM CaC1₂. Nuclei were collected through double filtration and two 1.0 M sucrose density gradient centrifugations. After the nuclei were washed, microscopic examination revealed a purity of over 90%. Radioactive assays of the nuclear preparations demonstrated phosphodiesterase activity consistant with that indicated by cytochemical localization. The specific activity of the nuclear enzyme was 15 nMole of cyclic AMP hydrolyzed /min/mg. of protein

Planning Experience in Tunisia, Burundi and Syria

In a 1975 CRED Discussion Paper (#46), the present author analyzed the financing of investments in Tunisia during the period 1961-1971. Since then, the author has gained further planning experience in Burundi and Syria. This paper will describe the planning tools developed in these three countries and will discuss their general applicability. In Tunisia, a system of interlocking capital accounts was developed in order to analyse past investments. In Burundi, this system of interlocking capital accounts was computerized and used for macroeconomic forecasts. Over the years, other elements were added to the macroeconomic framework, in order to provide detailed forecasts in various fields: production, requirements of skilled personnel, etc. Moreover, a computerized list of projects and an educational model were established. Finally, in Syria, the production element was further developed into an industrial development model. This model was based on balance equations of individual commodities and on input-output relations between them. Such a computerized commodity model corresponds very closely to Syrian planning methods, applied manually.Center for Research on Economic Development, University of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/100813/1/ECON272.pd

What about me? : the final question of a suicidal teen

Adolescents need access to vital information on how to help a friend who is contemplating suicide. They need to be able to identify the signs and seek assistance from an understanding adult. This research project, What About Me? The final question of a suicidal teen, was designed to determine whether reading an adolescent novel can educate teens about depression and suicide awareness. I wrote the adolescent novel so young adolescents would be able to relate to the main character and learn from her mistakes

A look at administrative qualities for success : a reflective essay

It is not just having a degree, and a few classes that help to make a person a good administrator. It is having an understanding and passion about ones own personal beliefs and core values that will help to make the difference between a good administrator and a great administrator. In the following paper professionalism, leadership, morality, and learning will be discussed further. Examining how each of these areas are important qualities for an administrator to develop and maintain as a leader in a school

The Control of Annual Plans: The Experience of Tunisia

Tunisia has been preparing annual economic plans since 1966. Monthly data began to be collected in 1968 in order to assess whether things are moving as foreseen in the annual plan. Three examples of monthly data are discussed in this paper: government capital budget, industrial output, and private investment, to show how their progress is studied in relation to changes in other sectors of the economy.Center for Research on Economic Development, University of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/100815/1/ECON274.pd

What I believe about leadership and education

Educational leadership should focus on excellence much like that found in the military, medicine, professional athletics, and business. With current educational focus on student achievement and proficiency educational leaders must strive for encompassing excellence throughout the school. Leadership directing this excellence must include designing effective professional development, have a clear vision, and implement programs towards standards-based instruction. To drive towards this excellence educational leaders must be effective communicators, reflective thinkers, and be willing to share leadership