A novel mode of asymmetric division identifies the fly neuroglioblast 6-4T.

Asymmetric cell divisions and segregation of fate determinants are crucial events in the generation of cell diversity. Fly neuroblasts, the precursors that self-reproduce and generate neurons, represent a clear example of asymmetrically dividing cells. Less is known about how neurons and glial cells are generated by multipotent precursors. Flies provide the ideal model system to study this process. Indeed, neuroglioblasts (NGBs) can be specifically identified and have been shown to require the glide/gcm fate determinant to produce glial cells, which otherwise would become neurons. Here, we follow the division of a specific NGB (NGB6-4T), which produces a neuroblast (NB) and a glioblast (GB). We show that, to generate the glioblast, glide/gcm RNA becomes progressively unequally distributed during NGB division and preferentially segregates. Subsequently, a GB-specific factor is required to maintain glide/gcm expression. Both processes are necessary for gliogenesis, showing that the glial vs. neuronal fate choice is a two-step process. This feature, together with glide/gcm subcellular RNA distribution and the behavior of the NGB mitotic apparatus identify a novel type of division generating cell diversity.

Gliogenesis depends on glide/gcm through asymmetric division of neuroglioblasts.

Some neurons and glial cells originate from neuroblasts and glioblasts, stem cells that delaminate from the ectoderm of developing fly embryos. A second class of glial cells and neurons differentiates from multipotent precursors, the neuroglioblasts. The differentiation of both glial cell types depends on glial cell deficient/glial cell missing (glide/gcm). Although it has been shown that this transcription factor promotes gliogenesis at the expense of neurogenesis, the cellular mechanisms underlying this fate choice are poorly understood. Using loss and gain of function glide/gcm mutations here we show that the cell fate choice takes place in the neuroglioblast, which divides and produces a glioblast and a neuroblast. Such choice requires the asymmetric distribution of glide/gcm RNA, which accumulates preferentially on one side of the neuroglioblast and is inherited by one cell, the presumptive glioblast. Interestingly, glial cells can differentiate from cells that delaminate as neuroglioblasts or they can arise from cells that start expressing glide/gcm several hours after delamination of a neuroblast. Altogether, these findings identify a novel type of asymmetric cell division and disclose the lineage relationships between glia and neurons. They also reveal the mode of action of the glide/gcm promoting factor.

Positive autoregulation of the glial promoting factor glide/gcm.

Fly gliogenesis depends on the glial-cell-deficient/glial-cell-missing (glide/gcm) transcription factor. glide/gcm expression is necessary and sufficient to induce the glial fate within and outside the nervous system, indicating that the activity of this gene must be tightly regulated. The current model is that glide/gcm activates the glial fate by inducing the expression of glial-specific genes that are required to maintain such a fate. Previous observations on the null glide/gcmN7-4 allele evoked the possibility that another role of glide/gcm might be to maintain and/or amplify its own expression. Here we show that glide/gcm does positively autoregulate in vitro and in vivo, and that the glide/gcmN7-4 protein is not able to do so. We thereby provide the first direct evidence of both a target and a regulator of glide/gcm. Our data also demonstrate that glide/gcm transcription is regulated at two distinct steps: initiation, which is glide/gcm-independent, and maintenance, which requires glide/gcm. Interestingly, we have found that autoregulation requires the activity of additional cell-specific cofactors. The present results suggest transcriptional autoregulation is a mechanism for glial fate induction.

Glial differentiation does not require a neural ground state.

Glial cells differentiate from the neuroepithelium. In flies, gliogenesis depends on the expression of glial cell deficient/glial cell missing (glide/gcm). The phenotype of glide/gcm loss- and gain-of-function mutations suggested that gliogenesis occurs in cells that, by default, would differentiate into neurons. Here we show that glide/gcm is able to induce cells even from a distinct germ layer, the mesoderm, to activate the glial developmental program, which demonstrates that gliogenesis does not require a ground neural state. These findings challenge the common view on the establishment of cell diversity in the nervous system. Strikingly, ectopic glide/gcm overrides positional information by repressing the endogenous developmental program. These findings also indicate that glial differentiation tightly depends on glide/gcm transcriptional regulation. It is likely that glide/gcm homologs act similarly during vertebrate gliogenesis.

glide/gcm is expressed and required in the scavenger cell lineage.

Glial cell differentiation in Drosophila melanogaster requires the activity of glide/gcm (glial cell deficient/glial cell missing). The role of this gene is to direct the cell fate switch between neurons and glial cells by activating the glial developmental program in multipotent precursor cells of the nervous system. In this paper, we show that glide/gcm is also expressed and required in the lineage of hemocytes/macrophages, scavenger cells that phagocytose cells undergoing programmed cell death. In addition, we show that, as for glial cells, glide/gcm plays an instructive role in hemocyte differentiation. Interestingly, it has been shown that in the development of the fly adult nervous system the role of scavenger cells is played by glial cells. These data and our findings on the dual role of glide/gcm indicate that glial cells and hemocytes/macrophages are functionally and molecularly related.

[Predictive significance of reticulocyte count (interpretative methodologic approach)]. / Significato predittivo del conteggio dei reticolociti (approccio metodologico interpretativo).

This study concerns the comparison of two methodologies for reticulocyte count on two groups of 100 subjects. The evaluation of the results achieved with the two colorants (brilliant cresyl blue and pre-colored glasses with crystal acetate violet and methylene blue) suggests the application of more reliable parameters (reticulocyte index, reticulocyte production index) for the interpretation of reticulocyte counting. It seems desirable to correct the absolute reticulocyte number with the degree of anemia of the patient and to calculate the medullary production index to identify the effective reticulocytosis.

[Macro-CK type 1: a methodological study approach and its clinical significance]. / Macro-CK tipo 1: approccio metodologico di indagine e suo significato clinico.

Description of an analytical procedure in order to show the atypical-CK carriers that simulate an abnormal raising of CK-MB circulating levels in dosages for immune inhibition. This procedure was applied to two samples taken from patients of such a type, immune form neoplastic and cardiac pathology. A systematic dosage of a "real" MB isoenzyme is desirable in all the cases of very raised CK-MB activity.

[The significance of antipolysaccharide C antibodies from Streptococcus group A. Their importance in the diagnosis of streptococcal infections]. / Sul significato degli anticorpi antipolisaccaride C dello streptococco di gruppo A. La loro importanza nella diagnosi di infezione streptococcica.

Here is underlined the role of quantitative determination of streptococcus A polysaccharide C antibody for the diagnosis of streptococcal infection. The Authors suggest to associate this determination with antistreptolysin titer and/or bacterial esoenzyme antibody titer, in order to achieve a wider spectrum of streptococcus induced antibodies for therapeutic and prophylactic applications.

[Value of various hematologic indexes proposed for identifying healthy carriers of the beta-thalassemic trait]. / Considerazioni sul valore di alcuni indici ematologici proposti per identificare il portatore sano del trait beta-talassemico.

The results of a screening for beta-heterozygous thalassemia conducted on 999 school-boys aged from 11 to 13 are the following: 7.5% of the subjects were taker of the thalassemia trait; 74 subjects over 75 with beta-heterozygous thalassemia had "Mean Corpuscolar Volume" (MCV) values below 70 fl. The results of the subjects with globular volume less than or equal to 79 fl (with or without beta-thalassemia) were used to compare the diagnostic accuracy of beta-thalassemia for the hematological indexes of England-Fraser, Mentzer, Shine-Lal and the MCV estimations. This comparison has shown better results in terms of sensibility and specificity for MCV with respect to the other indexes. A more extensive application of the study could be convenient in order to evaluate if the MCV level of 70 fl is effective to discriminate between beta-thalassemia and non thalassemic microcytosis.

Some biochemical platelet patterns in stable coronary patients.

Patients affected by stable angina pectoris whose platelets were characterized by ultrastructural alterations, were investigated in some biochemical changes of their platelets. A decrease of P.A.R. (platelet aggregate ratio), an increase of MDA production in particular conditions, nevertheless a stability of cAMP content in platelets, even after thrombin stimulation, were found.