Jaime Gómez-Márquez

Prothymosin α is a nuclear protein

Prothymosin α, a protein first isolated from rat thymus and widely distributed in animal tissues, has an attributed role in the stimulation of the immune system. Its structure contains thymosin α1, a Glu‐rich domain and a putative nuclear location signal. Furthermore, the amount of this protein seems to be associated with the relative size of the nucleus and is inducible during cell growth. We postulate that prothymosin α is located inside the cell nucleus and that its activity might be to organize some protein complexes.

High levels of mouse thymosin β4 mRNA in differentiating P19 embryonic cells and during development of cardiovascular tissues

The self assembly of actin and the large number of actin-binding proteins are important in the establishment of cell shape and function during embryogenesis. Thymosin beta4 (Tbeta4) is a small acidic peptide that participates in the regulation of actin polymerization in mammalian cells. In the present work, we report the presence of the mRNA encoding for Tbeta4 in mouse embryonic stem cells and its induction in P1 9 embryonal cells stimulated to differentiate into ectodermal-like (neurons and glia) or mesodermal-like cells (cardiac and skeletal muscle). The induction of Tbeta4, mRNA in P19 cells was confirmed by in situ hybridization analysis of early mouse postimplantation embryos. Noteworthy, we observed an important hybridization signal in several areas of the embryo specially in blood vessels and in heart tissues, suggesting a role for this peptide in angiogenesis. In conclusion, the results presented here demonstrate the expression of Tbeta4 gene during early embryogenesis which immediately suggests an important role for this peptide in developmental processes requiring actin-based functions such as the formation of cardiovascular system.

Expression of thymosin β4 messenger RNA in normal and kainate-treated rat forebrain

Thymosin beta4 is a major actin-sequestering peptide widely distributed in mammalian tissues, including the nervous system. In the present study, we analyse the expression of thymosin beta4 in normal and kainate-treated rat forebrain. In untreated animals, thymosin beta4 messenger RNA is mainly expressed in neurons of the hippocampal formation, neocortex and amygdaloid complex, as well as in oligodendrocytes. Other high-expressing areas are the tanycytic ependyma of the infundibulum, the substantia nigra pars compacta, and the supraoptic and premammillary nuclei. In rats treated with kainate, an excitotoxin that induces synaptic activation in the CA1-CA3 pyramidal neurons of the hippocampus, the levels of thymosin beta4 were clearly increased in the hippocampus and neocortex during the first 2-3 h after injection. In the long term, kainate causes neuronal degeneration in the CA1-CA3 regions of the hippocampus and functionally related structures, provoking a depletion of thymosin beta4 messenger RNA in these areas; however, the levels of this transcript are restored two weeks after kainate injection. Moreover, we have found that, in these degenerating zones, gliosis is accompanied by an elevation of the levels of thymosin beta4 messenger RNA, particularly in the CA1-CA3 region of the hippocampus, the lateral geniculate nucleus and the mammillothalamic tract. The present results demonstrate the existence of relatively high levels of thymosin beta4 messenger RNA in several areas of the rat forebrain, indicating that this peptide plays an important role in the regulation of actin polymerization in these regions of the brain. Moreover, the elevation of this messenger RNA after kainate treatment suggests a function of thymosin beta4 in the production and remodelling of neuronal processes. Finally, our findings provide evidence for a participation of this actin-sequestering molecule in the reactivity of certain types of glial cell that follows kainate lesions.

Differential expression of thymosins β4 and β10 during rat cerebellum postnatal development

The β-thymosins are a family of actin monomer-sequestering proteins widely distributed among vertebrate classes. The most abundant β-thymosins in mammalian species are thymosin β4 (Tβ4) and thymosin β10 (Tβ10), two small peptides (43 amino acids) sharing a high degree of sequence homology. In the present work, we have analyzed the distribution of Tβ4 and Tβ10 in the developing and adult rat cerebellum using in situ hybridization and immunohistochemistry techniques. Our results show that the temporal and cellular patterns of expression of both β-thymosins are different. In the young (7 and 18 postnatal days) and adult (1 and 4 months old) rat cerebellum, Tβ4 was mainly expressed in the glia (microglia, Golgi epithelial cells and oligodendrocytes), neurons (granule cells and Purkinje cells), and in the capillaries. In 14-month-old rats, the Tβ4 immunoreactivity was only detected in some microglia cells. In young and adult animals, most of the Tβ10 immunoreactivity was localized in several types of neuronal cells including granule cells, Golgi neurons and Purkinje cells. In old animals, a faint Tβ10 signal could be detected in a few Purkinje cells. Our results suggest that each β-thymosin could play a different function in the control of actin dynamics.

The beta-thymosins, small actin-binding peptides widely expressed in the developing and adult cerebellum.

The beta-thymosins are a highly conserved family of small polar peptides known to bind monomeric actin and inhibit its polymerization. The beta-thymosins show a high degree of sequence conservation among all vertebrate classes and they have been also identified in some invertebrate phyla. The most abundant beta-thymosins in mammals are thymosin beta4 (Tbeta4) and thymosin beta10 (Tbeta10), two ubiquitous small (43 amino acids) peptides sharing a high degree of sequence homology. Both beta-thymosins are present in virtually all mammalian tissues and cells studied, showing distinct patterns of expression in several tissues. The beta-thymosins are expressed in the developing and mature nervous system, indicating their participation with other actin-binding peptides in the control of actin polymerization. In the rat cerebellum the temporal and cellular patterns of expression of Tbeta4 and Tbeta10 are different, suggesting that each beta-thymosin could play a specific physiological function during cerebellum development. The possible roles of beta-thymosins in the developing mammalian cerebellum are discussed.

Thymosin β10 mRNA expression during early postimplantation mouse development

The β‐thymosins are a family of monomeric actin sequestering peptides that regulate actin dynamics within the cells. During embryogenesis the control of actin polymerization is essential in processes such as cell migration, angiogenesis and neurogenesis. Here we report that the levels of thymosin β 10 (Tβ 10) mRNA strongly increase during early postimplantation mouse embryogenesis as well as during in vitro P19 cell differentiation, indicating that this peptide plays an important role in early development. Moreover, analysis of the spatial distribution of Tβ 10 mRNA in 9.5–12.5 days postcoitum mouse embryos showed a remarkable presence of this transcript in mesenchymal structures as well as in the mantle layer of spinal cord. Interestingly, we observed differences in the distribution of the mRNAs encoding Tβ 10 and Tβ 4, another member of the β‐thymosin family, suggesting different roles for these peptides during mouse embryogenesis.

The thymosin β4 gene is strongly activated in neural tissues during early postimplantation mouse development

We studied the temporal and spatial distribution of the mRNA encoding for thymosin beta 4 (T beta 4), a small acidic actin-sequestering peptide, during the early postimplantation mouse development. Analysis of total embryo RNA demonstrated a strong activation of T beta 4 gene after gastrulation and coincident with neurulation. In situ hybridization showed that T beta 4 mRNA was strongly expressed in the central nervous system and peripheral ganglia, paralleling the gradient of neuronal differentiation. An intense signal was also observed in intraventricular macrophages and blood vessels. The role of T beta 4 in mammalian neuroembryogenesis is discussed.

Inhibition of DNA synthesis by K + -stabilised G-quadruplex promotes allelic preferential amplification

PCR preferential amplification consists of the inefficient amplification of one allele in a heterozygous sample. Here, we report the isolation of a GC‐rich human minisatellite, MsH43, that undergoes allelic preferential amplification during PCR. This effect requires the existence of a (TGGGGC)4 motif that is able to form a G‐quadruplex in the presence of K+. This structure interferes with the DNA synthesis of the alleles harbouring this motif during PCR The present results are the first demonstration that the formation of G‐quadruplex can be one of the mechanisms involved in some kinds of preferential amplification.

Transcript levels of thymosin β4, an actin-sequestering peptide, in cell proliferation

Thymosin beta 4 (beta 4) is an ubiquitous 5-kDa peptide that has been identified as an actin-sequestering peptide. In this work, Northern blot analysis was used to study the beta 4 mRNA levels during the cell cycle of rat thymocytes and hepatocytes as well as in human lymphocytes from patients with leukemia. beta 4 mRNA was found in all the stages of thymocyte and hepatocyte cell cycle, showing an increase in the S-phase which was maintained during the G2 and M phases. Incubation of splenic T-cells with concanavalin A, phorbol myristate acetate or the ionophore A23187 lead to a similar increase of beta 4 transcript during the S-phase. The increase in beta 4 mRNA observed in the G2/M boundary of the cell cycle, together with its ability to inhibit actin polymerization, suggests a possible role of beta 4 in the the morphological changes and actin redistribution occurring during the cytokinesis.

Function of Prothymosin α in Chromatin Decondensation and Expression of Thymosin β-4 Linked to Angiogenesis and Synaptic Plasticity

Abstract:  Prothymosin α (ProTα) is an abundant highly acidic protein found in the nuclei of virtually all mammalian cells. The expression of this protein is increased in proliferating mammalian cells. However, the function of this molecule is still controversial. Here I present a model explaining the role of this protein in chromatin decondensation through its interaction with histone H1. β‐thymosins are a family of small actin‐binding peptides widely distributed in eukaryotic cells. Here I will focus on thymosin β‐4, the most abundant member of this family. In particular, I will discuss its expression in the mammalian development of cardiovascular and nervous systems as well as its implications in neuronal plasticity.