sup], With regard to the downstream signals of p16 (INK4a), p16 activates the pRB tumor suppressor, which silence certain pro-proliferative genes by heterochromatinization
, thereby instituting a stringent arrest of cell proliferation.
The first approach on the probable origin of this chromosome was performed by Salvador and Moreira-Filho (1992), who considered that a non-disjunction, followed by heterochromatinization
, could be associated with its emergence.
Changed genome heterochromatinization
upon prolonged activation of the Raf/ERK signaling pathway.
, chromatin elimination and haploidization in the parahaploid mite Metaseiulus occidentalis (Nesbitt) (Acarina: Phytoseiidae).
Today we know that such differential heteropycnosis is due to facultative heterochromatinization
, due to epigenetic changes of the X chromosome chromatin.
In one species, Schizocosa malitiosa, only one X chromosome was notable in that it exhibited complete heterochromatinization
(Brum-Zorrilla & Cazenave 1974; Brum-Zorrilla & Postiglioni 1980; Rowell 1985; Datta & Chatterjee 1988; Rowell 1991b).
However, White's contribution to the origin and evolution of sex chromosomes was substantial, in his identification of processes of differentiation between neo-sex XY systems involving chromosomal rearrangements, heterochromatinization and loss of crossing-over potential, a problem also addressed by the great South American cytologist Francisco A.
Of course, now we know that changes other than structural aid the differentiation of the neo-Y, such as accumulation of noncoding sequences and heterochromatinization (see below).
1959), by gradual heterochromatinization
and erosion of the Y sex chromosome.
After Robertsonian fusions take place (Saez 1963, White 1973), agradual process of heterochromatinization in the exhomologues begins.
Gradient of the heterochromatinization in the evolution of the sexual system neoX-neoY.
In spite of the fact that we used conventional stain, no progressive heterochromatinization
was observed in the neo-Y, indicating that this mechanism has been acquired recently and contrasting with what happened in the neo-X system of certain orthopterans (Saez 1963; White 1973a, 1973b, 1973c; Ferreira 1975; Ferreira & Mesa 1979; Mesa 1973; Mesa & Mesa 1967) that are at the end of the neo-XY evolutionary process, with both X and Y wholly heterochromatic during first prophase.