Joana Santos

ESCs Require PRC2 to Direct the Successful Reprogramming of Differentiated Cells toward Pluripotency

Embryonic stem cells (ESCs) are pluripotent, self-renewing, and have the ability to reprogram differentiated cell types to pluripotency upon cellular fusion. Polycomb-group (PcG) proteins are important for restraining the inappropriate expression of lineage-specifying factors in ESCs. To investigate whether PcG proteins are required for establishing, rather than maintaining, the pluripotent state, we compared the ability of wild-type, PRC1-, and PRC2-depleted ESCs to reprogram human lymphocytes. We show that ESCs lacking either PRC1 or PRC2 are unable to successfully reprogram B cells toward pluripotency. This defect is a direct consequence of the lack of PcG activity because it could be efficiently rescued by reconstituting PRC2 activity in PRC2-deficient ESCs. Surprisingly, the failure of PRC2-deficient ESCs to reprogram somatic cells is functionally dominant, demonstrating a critical requirement for PcG proteins in the chromatin-remodeling events required for the direct conversion of differentiated cells toward pluripotency.

Heterokaryon-based reprogramming of human B lymphocytes for pluripotency requires Oct4 but not Sox2.

Differentiated cells can be reprogrammed through the formation of heterokaryons and hybrid cells when fused with embryonic stem (ES) cells. Here, we provide evidence that conversion of human B-lymphocytes towards a multipotent state is initiated much more rapidly than previously thought, occurring in transient heterokaryons before nuclear fusion and cell division. Interestingly, reprogramming of human lymphocytes by mouse ES cells elicits the expression of a human ES-specific gene profile, in which markers of human ES cells are expressed (hSSEA4, hFGF receptors and ligands), but markers that are specific to mouse ES cells are not (e.g., Bmp4 and LIF receptor). Using genetically engineered mouse ES cells, we demonstrate that successful reprogramming of human lymphocytes is independent of Sox2, a factor thought to be required for induced pluripotent stem (iPS) cells. In contrast, there is a distinct requirement for Oct4 in the establishment but not the maintenance of the reprogrammed state. Experimental heterokaryons, therefore, offer a powerful approach to trace the contribution of individual factors to the reprogramming of human somatic cells towards a multipotent state.

TRIM28/KAP1 regulates senescence

Senescence is a highly stable cell cycle arrest which limits the replication of cells with damaged genomes. The senescence program is activated during aging or in response to insults like DNA damage or oncogenic signaling. Upon induction of senescence, cells undergo profound changes on their transcription program, chromatin organization, and they secrete a complex mixture of mainly pro-inflammatory components termed the senescence-associated secretory phenotype (SASP). The SASP mediates multiple effects, including reinforcing senescence and activating immune surveillance responses. Given the important role that senescence has in aging, cancer and other pathologies, identifying mechanisms regulating senescence has therapeutic potential. Here we describe a role for TRIM28 (also known as KRAB-associated protein 1, KAP1) on mediating oncogene-induced senescence (OIS). TRIM28 accumulates during OIS becoming phosphorylated on serine 824. To investigate the role of TRIM28, we knocked down its expression and observed that the depletion of TRIM28 partially prevented cell arrest during OIS. While induction of p53 and p21 during OIS, was not affected by TRIM28 depletion, p16(INK4a) induction was partially prevented. Finally, we observed that the induction of IL8, IL6 and other SASP components were strongly suppressed upon TRIM28 depletion. In conclusion, the above-described results show that TRIM28 regulates senescence and affects the induction of the senescence-associated secretory phenotype.

Ecologia da polinização de Ipomoea longistaminea O?Donell (Convolvulaceae) na região semiárida da Bahia.

Ipomoea longistaminea se destaca entre as especies do genero por ser considerada como endemica da Caatinga e de distribuicao restrita nos Estados de Pernambuco e da Bahia. Neste trabalho, foi estudada a biologia da e produtiva e os visitantes florais dessa especie em area de Caatinga, na Fazenda Sao Luiz, em Juazeiro-BA. As atividades foram desenvolvidas nos anos de 2009 a 2012, no periodo de maio a agosto, entre 05h00 e 18h00, com 20 individuos de I. longistaminea. Para o estudo da biologia floral, flores foram marcadas e acompanhadas, sendo anotadas a antese e os visitantes florais. Experimentos de polinizacao foram feitos para determinar a estrategia reprodutiva. Ipomoea longistaminea e uma liana anual, como floracao observada de maio a julho, caracterizada como do tipo cornucopia. As inflorescencias sao do tipo cimeira apresentando, em media, 10,6 ± 2,88 botoes. As flores sao infundibuliformes, com corola de cor vermelha e comprimento medio de 40,9 ± 3,68mm. O androceu e composto por cinco estames que, juntamente com estilete e estigma, fica exposto fora da corola. A antese e diurna, ocorrendo por volta das 05h00 e, nesta fase, o estigma esta receptivo, o polen esta viavel (93,4%) e disponivel e o nectar e produzido em pequena quantidade (7,1 ± 2,1μL). Por volta das 15h00, as flores encontram-se com as petalas desidratadas, fechando a fauce da corola. Ao longo da floracao, foram registradas visitas de cinco especies de beija-flores e tres especies de abelhas. Ipomoea longistaminea e uma especie autocompativel e que apresenta atributos florais caracteristicos da sindrome de ornitofilia, sendo Chlorostilbon sp., Eupetomena macroura e o beija-flor nao identificado seus polinizadores potenciais no local do presente estudo.