Toxoplasma gondii has two lineages of histones 2b (H2B) with different expression profiles

DALMASSO, MC; ECHEVERRIA, PC; ZAPPIA, MP; HELLMAN, U; DUBREMETZ, JF; ANGEL, SO

MOLECULAR AND BIOCHEMICAL PARASITOLOGY

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2006 vol. 148 p. 103 - 107

0166-6851

Apicomplexa are obligate intracellular parasite that invade and develop within host cells. Toxoplasma gondii shares these characteristics but is unusual in its ability to infect a wide range of intermediate hosts. A hallmark of the asexual cycle is the equilibrium between the rapidly dividing tachyzoite and the more slowly dividing bradyzoite, which is essential for disease propagation and causation. Tachyzoites are responsible for dissemination of infection during the acute phase of disease and congenital neurological birth defects; whereas bradyzoites forms dormant cysts that can remain latent within the tissues for many years, representing a threat to immunocompromised patients. Interconversion between tachyzoites and bradyzoites not only plays a pivotal role in establishing a chronic infection, but it is also responsible for disease reactivation. Thus, understanding the mechanism(s) that regulates development in this parasite is of critical importance. The induction of bradyzoite development in vitro has been associated with changes in temperature, pH, and other stress inducers but the mechanisms that regulate the transition between these two stages are not clearly understood. Differentiation does not occur if tachyzoite growth is blocked and thus cell cycle progression appears to be a prerequisite for development. Tachyzoite division cycle consists primarily of G1 and S phases with mitosis following immediately upon the conclusion of DNA replication. Under stress conditions division cycle slows, a unique late-S/G2 population appears and the onset of bradyzoite development becomes evident. Histones constitute the fundamental component of chromatin and play a fundamental role in packaging DNA into nucleosomes. The nucleosome core consists of an octamer of four histones, H2A, H2B, H3 and H4 around which a 146 base pairs stretch of DNA is wrapped. They are responsible of the chromatin state during DNA replication and cell cycle progression, spatially and temporally coordinated gene expression, as well as DNA repair and recombination events. In higher eukaryotes histone biosynthesis is restricted to the S-phase, occurring simultaneously with DNA synthesis and chromosome replication. In the Apicomplexa Plasmodium falciparum H2B mRNA are differentially regulated during the life-cycle as well as during differentiation. Recently, a correlation between H3 and H4 acetylation status and stage-specific gene expression in T. gondii was observed. In this article, two Toxoplasma gondii histones H2B (TgH2Bv1 and TgH2Bv2) were identified and characterized. It was demonstrated that their expression were differentially regulated in both tachzyoite and bradyzoite stages.