Un nuevo modelo para el estudio de la diferenciación de las células madre (stem cells)los nidos de regeneración de locusta

Resumen

UN NUEVO MODELO PARA EL ESTUDIO DE LA DIFERENCIACIÓN DE LAS CÉLULAS MADRE (STEM CELLS): LOS NIDOS DE REGENERACIÓN DE LOCUSTA RESUMEN: THE REGENERATIVE NIDI OF THE LOCUST MIDGUT AS a MODEL TO STUDY EPITHELIAL CELL Differentiation FROM STEM CELLS A better knowledge of the regulatory mechanisms involved in stem cell proliferation and/or differentiation could open new ways for the treatment of some diseases. Most studies in the field of stem cell biology have been carried out on cultured isolated cells. in the case of adult tissue stem cells, mostly mesenchymal bone marrow derived cells have been studied, while the undifferentiated stem cells present in the epithelial tissues are less characterized. ln order to further advance our understanding on epithelial tissue stem cells, new in vivo models are required. The present study is focused on the dynamics of a new and simple model of intestinal epithelial regeneration found in the midgut of the desert locust Locusta migratoria (Linnaeus, 1758). The locust midgut consist on three cell types: columnar cells, endocrine cells and undifferentiated regenerative clustered cells. The midgut undifferentiated cells are the origin of the other two cell types, and are located in a nest of regenerative cells called regenerative niche. we have performed single and continuous Bromodeoxyuridine (Brdu) administration experiments to study the regeneration ni ches and their cellular dynamics. Immunocytochemistry and immunofluorescence techniques were used to detect Brdu incorporation in the regenerative niches and the expression of tetrapeptide FMRFa, as a marker for endocrine cell differentiation. At the niche base some isolated (0,15 cells per mm) BrdU-labelled cells (labelling retaining cells (lrc)) were observed 10-15 days after the last Brdu administration. We propose that these cells are the stem cells of this epithelial tissue. We all so calculated the length of the cell cycle phases for a subpopulation of transient amplification cells within the regenerative niche which will give rise to the columnar epithelial non endocrine lineage: Gl 2,5 ± 0,5 hours, S 5,5 ± 0,5 hours, G2 0,75 ± 0,25 hour and M 2,5 ± 0,5 hours. The differentiation of an endocrine cell from a niche stem cell is a less frequent event, which leads to a lower proportion of endocrine cells as compared to epithelial columnar digestive cells (up to 3 endocrine cells per niche). Endocrine cell commitment seems to occur very early in the differentiation process within the niche, as double labelled Brdu and fmrf positive endocrine cell have never been found in the present study, except in the case of the ampullar region through which Malpighian tubules drain to the midgut, where a higher activity of endocrine cell generation is found. In this area of the midgut 10% of the FMRFa-immunoreactive cells are also Brdu positive after a continuous (4 days) administration of the S-phase marker. In summary, we have characterized a new and simple animal model of epithelial regeneration from stem cells that may be useful to understand the complex biology that drives the renewal of epithelial tissues from progenitor undifferentiated and uncommitted cells