No abstract

-The effect of caponisation on carcass composition by parts and tissues was examined. Twenty-eight castrated and twenty male Penedesenca Negra chicks reared under free-range conditions were slaughtered at 28 weeks of age. The birds were castrated at 4 or 8 weeks. The left sides of the carcasses were quartered (wing, breast, thigh and drumstick), and the parts dissected into the tissue components (skin, subcutaneous fat, intermuscular fat, muscle, bone and tendons). Capons showed more abdominal, intermuscular and subcutaneous fat than the cocks, both at the same slaughter age and at the same weight. The breast and thigh were heavier in the capons than in the cocks. However, the whole muscle mass in the breast was increased by caponisation. This favourable effect was achieved at the expense of decreasing the carcass yield. The age of castration up to 8 weeks did not affect the carcass composition of the parts and tissues. chicken / capon / carcass / tissue composition Résumé -Comparaison du rendement à la découpe et de la composition tissulaire des carcasses de coqs et de chapons. Vingt huit chapons et vingt coqs de la race Penedesenca Negra ont été élevés sur parcours et abattus à l'âge de 28 semaines. Le chaponnage des poulets a été réalisé à deux âges différents : 4 ou 8 semaines. Après l'abattage, les morceaux (aile, pilon, cuisse et filet) correspondant à la moitié gauche de la carcasse ont été prélevés et disséqués en séparant la peau, le tissu adipeux sous-cutané, le tissu adipeux intermusculaire, les muscles, les os et les tendons. Par comparaison avec les coqs abattus au même âge ou de même poids, les chapons présentent une quantité de gras abdominal sous-cutané et intermusculaire plus élevée. Le poids de leur filet est également supérieur. En revanche, leur rendement en carcasse est inférieur. L'âge au chaponnage n'a pas d'effet sur le rendement à la découpe, ni sur la composition tissulaire de la carcasse.coq / chapon / carcasse / composition tissulaire 421

Cell cycle stimulation is a major transforming mechanism of Myc oncoprotein. This is achieved through at least three concomitant mechanisms: upregulation of cyclins and Cdks, downregulation of the Cdk inhibitors p15 and p21 and the degradation of p27. The Myc-p27 antagonism has been shown to be relevant in human cancer. To be degraded, p27 must be phosphorylated at Thr-187 to be recognized by Skp2, a component of the ubiquitination complex. We previously described that Myc induces Skp2 expression. Here we show that not only Cdk2 but Cdk1 phosphorylates p27 at the Thr-187. Moreover, Myc induced p27 degradation in murine fibroblasts through Cdk1 activation, which was achieved by Myc-dependent cyclin A and B induction. In the absence of Cdk2, p27 phosphorylation at Thr-187 was mainly carried out by cyclin A2-Cdk1 and cyclin B1-Cdk1. We also show that Cdk1 inhibition was enough for the synthetic lethal interaction with Myc. This result is relevant because Cdk1 is the only Cdk strictly required for cell cycle and the reported synthetic lethal interaction between Cdk1 and Myc.

The MAX network transcriptional repressor (MNT) is an MXD family transcription factor of the basic helix-loop-helix (bHLH) family. MNT dimerizes with another transcriptional regulator, MYC-associated factor X (MAX), and down-regulates genes by binding to E-boxes. MAX also dimerizes with MYC, an oncogenic bHLH transcription factor. Upon E-box binding, the MYC–MAX dimer activates gene expression. MNT also binds to the MAX dimerization protein MLX (MLX), and MNT–MLX and MNT–MAX dimers co-exist. However, all MNT functions have been attributed to MNT–MAX dimers, and no functions of the MNT–MLX dimer have been described. MNT's biological role has been linked to its function as a MYC oncogene modulator, but little is known about its regulation. We show here that MNT localizes to the nucleus of MAX-expressing cells and that MNT–MAX dimers bind and repress the MNT promoter, an effect that depends on one of the two E-boxes on this promoter. In MAX-deficient cells, MNT was overexpressed and redistributed to the cytoplasm. Interestingly, MNT was required for cell proliferation even in the absence of MAX. We show that in MAX-deficient cells, MNT binds to MLX, but also forms homodimers. RNA-sequencing experiments revealed that MNT regulates the expression of several genes even in the absence of MAX, with many of these genes being involved in cell cycle regulation and DNA repair. Of note, MNT–MNT homodimers regulated the transcription of some genes involved in cell proliferation. The tight regulation of MNT and its functionality even without MAX suggest a major role for MNT in cell proliferation.