Biomedical subjects

Michael Schebesta

Publications and source records attributed to Michael Schebesta.

7 recordsLinked to original sources

PubMed2006

Anillin localization defect in cardiomyocyte binucleation.

Heart growth is augmented during early development by cardiomyocyte proliferation. In contrast, heart growth during postnatal life occurs by increasing cell size. Postnatal cardiomyocytes can undergo DNA synthesis, mitosis and binucleation. However, they lose the ability to complete cytokinesis. The underlying mechanism is poorly understood. It has been suggested that incomplete disassembly of contractile elements prohibits cytokinesis. Here, we show that serum-induced binucleation results in the normal disassembly of the contractile apparatus. In contrast, analysis of Aurora B and Anillin localization demonstrates that binucleation is characterized by asymmetric constriction, delay of furrow constriction and defective mid-body formation. Anillin fails to focus at the cortex in anaphase and shows an expanded localization around the mid-body during cytokinesis. p38 inhibition rescues the mid-body formation defect. We show that p38 accumulates during cytokinesis at the mid-body and suggest that p38 activity has a regulatory role in cytokinesis. Microarray analysis reveals that p38 inhibition upregulates core components of the central spindle. Taken together, our results demonstrate that postnatal cardiomyocytes form a cleavage furrow and that binucleation is associated with an Anillin localization defect.

Animals↗

PubMed2006

Transcriptional profiling of caudal fin regeneration in zebrafish.

Regeneration of severed limbs in adult animals is restricted to urodele amphibians. Mammals, including humans, have very limited regenerative capabilities and even with proper treatment, only the tips of our digits can grow back. Teleost fish can regenerate amputated fins, the evolutionary ancestors of limbs. To elucidate the principles of limb-fin regeneration, we performed an Affymetrix microarray screen on regenerating caudal fins 12, 24, 48, and 72 h post amputation. Approximately 15,000 zebrafish transcripts were analyzed, identifying 829 transcripts as differentially expressed during regeneration. Of those, 563 were up-regulated and 266 were down-regulated. We constructed a comprehensive database containing expression data, functional assignment, and background information from the literature for each differentially expressed transcript. In order to validate our findings, we employed three approaches: (1) microarray expression analysis of genes previously implicated in fin regeneration, (2) RT-PCR analysis of genes newly identified as differentially expressed during regeneration, and (3) in situ hybridization of the up-regulated genes bambi, dlx5A, and her6. Moreover, we show that Smad 1/5/8 proteins, effector molecules of Bmp signaling, are phosphorylated during fin regeneration. Taken together, we provide a comprehensive database of fin regeneration that will serve as an important tool for understanding the molecular mechanisms of regeneration.

Animals↗

PubMed2006

Gene expression analysis of zebrafish heart regeneration.

Mammalian hearts cannot regenerate. In contrast, zebrafish hearts regenerate even when up to 20% of the ventricle is amputated. The mechanism of zebrafish heart regeneration is not understood. To systematically characterize this process at the molecular level, we generated transcriptional profiles of zebrafish cardiac regeneration by microarray analyses. Distinct gene clusters were identified based on temporal expression patterns. Genes coding for wound response/inflammatory factors, secreted molecules, and matrix metalloproteinases are expressed in regenerating heart in sequential patterns. Comparisons of gene expression profiles between heart and fin regeneration revealed a set of regeneration core molecules as well as tissue-specific factors. The expression patterns of several secreted molecules around the wound suggest that they play important roles in heart regeneration. We found that both platelet-derived growth factor-a and -b (pdgf-a and pdgf-b) are upregulated in regenerating zebrafish hearts. PDGF-B homodimers induce DNA synthesis in adult zebrafish cardiomyocytes. In addition, we demonstrate that a chemical inhibitor of PDGF receptor decreases DNA synthesis of cardiomyocytes both in vitro and in vivo during regeneration. Our data indicate that zebrafish heart regeneration is associated with sequentially upregulated wound healing genes and growth factors and suggest that PDGF signaling is required.

Animals↗

PubMed2005

p38 MAP kinase inhibition enables proliferation of adult mammalian cardiomyocytes.

Adult mammalian cardiomyocytes are considered terminally differentiated and incapable of proliferation. Consequently, acutely injured mammalian hearts do not regenerate, they scar. Here, we show that adult mammalian cardiomyocytes can divide. One important mechanism used by mammalian cardiomyocytes to control cell cycle is p38 MAP kinase activity. p38 regulates expression of genes required for mitosis in cardiomyocytes, including cyclin A and cyclin B. p38 activity is inversely correlated with cardiac growth during development, and its overexpression blocks fetal cardiomyocyte proliferation. Activation of p38 in vivo by MKK3bE reduces BrdU incorporation in fetal cardiomyocytes by 17.6%. In contrast, cardiac-specific p38alpha knockout mice show a 92.3% increase in neonatal cardiomyocyte mitoses. Furthermore, inhibition of p38 in adult cardiomyocytes promotes cytokinesis. Finally, mitosis in adult cardiomyocytes is associated with transient dedifferentiation of the contractile apparatus. Our findings establish p38 as a key negative regulator of cardiomyocyte proliferation and indicate that adult cardiomyocytes can divide.

Animals↗

PubMed2002

Transcriptional control of B-cell development.

Significant progress has recently been made in our understanding of how transcription factors such as PU.1, Notch1, E2A, EBF, Pax5, Bcl6, Blimp1 and XBP1 control different developmental decisions during the onset and terminal phase of B-lymphopoiesis. One emerging theme is that negative regulatory networks play an important role in suppressing alternative gene programs and their corresponding cell fates throughout B-cell development.

Animals↗

PubMed2002

Control of pre-BCR signaling by Pax5-dependent activation of the BLNK gene.

The developmental progression from pro-B to pre-B cells is controlled by pre-B cell receptor (pre-BCR) signaling which depends on BLNK (SLP-65) for coupling the Syk kinase to its downstream effector pathways. Here we identified BLNK as a direct target of the transcription factor Pax5 (BSAP). Restoration of BLNK expression in Ig(mu) transgenic Pax5(-/-) pro-B cells resulted in constitutive pre-BCR signaling and increased cell proliferation without inducing progression to the pre-B cell stage. Ig(mu)(+) Pax5(-/-) pro-B cells expressing a BLNK-estrogen receptor fusion protein initiated signaling immediately upon hormone addition, which facilitated analysis of pre-BCR-induced gene expression changes. The pre-BCR was shown to execute its checkpoint function by regulating genes involved in cell proliferation, intracellular signaling, growth factor responsiveness, and V(D)J recombination.

Adaptor Proteins, Signal Transducing↗

PubMed2002

Pax5 promotes B lymphopoiesis and blocks T cell development by repressing Notch1.

The B lineage commitment factor Pax5 (BSAP) is exclusively expressed in B lymphocytes of the blood system. To study the effect of Pax5 on the development of other hematopoietic lineages, we generated a heterozygous knockin mouse carrying a Pax5 minigene under the control of the Ikaros locus. Conditional and constitutive activation of the Ik(Pax5) allele demonstrated that precocious Pax5 expression in hematopoietic stem cells and progenitors failed to interfere with myeloid development and only weakly affected erythroblast formation. Instead, pan-hematopoietic Pax5 expression strongly promoted B cell development at the expense of T lymphopoiesis. Pax5 thereby interfered with T lineage commitment and early thymocyte development by repressing the transcription of the T cell specification gene Notch1.

Animals↗