Shafiq, T. | bioRxiv Science

bioRxiv2023

Three rules for epigenetic inheritance of human Polycomb silencing

Heritable expression of developmental genes is mediated by autoregulating transcription factor networks (TFNs) and Polycomb repressive chromatin silencing complexes (PRCs). Whether the mammalian Polycomb pathway mediates DNA sequence-independent epigenetic memory at genes being activated by TFNs remains unknown. Here, we show that, in human cells, newly induced Polycomb silencing at initially active developmental genes can be inherited for many cell divisions. However, when Polycomb silencing is similarly induced near ubiquitously expressed housekeeping genes, it is not heritable. Inheritance requires the recognition of CG-rich DNA by a Polycomb accessory protein, MTF2/PCL2, the histone H3 lysine 27 trimethylation (H3K27me3) and histone H2A lysine 119 mono-ubiquitination (H2AK119ub1) activities of PRC1 and PRC2, and their associated positive feedback (read-write). In the absence of H3K27me3, H2AK119ub1 can mediate inheritance of silencing by a mechanism that requires the recognition of H2AK119ub1 by the variant Polycomb Repressive Complex 1. These findings indicate that inheritance of Polycomb silencing in human cells (1) depends on sequence features of developmental gene loci (2) requires PRC1 and H2AK119ub1, and (3) can be mediated by PRC1-H2AK119ub1 independently of H3K27me3.

developmental biology↗

bioRxiv2022

Anatomical and Palynological Investigation within flora of Family Asteraceae

A comprehensive microscopic investigation of the leaf epidermis, as well as anatomical and palynological research of selected Asteraceae species from the flora of Havali (Kahutta) Azad Jammu and Kashmir (AJK) Pakistan, was carried out. This study includes 11 plant species comprising of Senecio jacobea, Leucanthemum vulgare, Halianthus annuus, Erigeron bonariensis, Achillea millifolium, Halianthus Linnaeus, Taraxacum officinale, Anaphalius nepalensis, Erigeron Canadensis, and Tagetes erecta. All the species studied were amphistomatic, with four different forms of stomata i.e tetracytic, anomocytic, anisocytic, and tricytic. The main stomatal type was tetracytic, followed by anomocytic. The abaxial epidermis has a higher stomatal density than the adaxial epidermis. Highest stomatal density was present Tagetes erecta while lowest is present in Conyza canadensis. In lower epidermis stomatal index was higher in Taraxacum officinale followed by Halianthus annuus and Tagetes erecta while in upper epidermis highest index was shown by Halianthus annuus. For this study species of family Acteraceae were properly collected. Furthermore, variation in pollen can be seen. List of palynomorph which includes family name, botanical name, local name, English name, flower colour, season and pollen description for the logical arrangement of these species. The logical ordering of these species was guided by dust characteristics such as form and pollen morphology. Palynological data has been found to be too big for taxonomists to calculate and make appropriate observations on their findings.

plant biology↗