An international team of scientists coordinated by Drs. Kim Worley and Jeffrey Rogers of the Baylor Human Genome Sequencing Center of Houston (USA) have completed the sequencing of the genome of the common titi. This is the first sequencing of a primate native to the American continent (New World monkeys). Two Spanish groups have participated in this research: one directed by Carlos López-Otín, at the Institute of Oncology of the University of Oviedo, with David Rodríguez, Xose S. Puente and Víctor Quesada, and one led by Tomás Marqués-Bonet, of the Institute of Evolutionary Biology (CSIC-UPF) of Barcelona, with Belén Lorente-Galdós.

The research has analyzed the genetic features of the farthest branch to humans of the evolutionary tree of the primates and complements the studies conducted in other closer branches, such as that of the orangutan or the chimpanzee, to which research groups of the University of Oviedo and the Institute of Evolutionary Biology have already contributed.

The research, which is being published today by the Nature Genetics journal, provides new information on the physiology of the titi, including peculiarities such as its reduced size and its particular reproductive system. Thus, this research reveals genetic features only seen in the titi, such as variants in the different genes that may be related to the fact that titis are the smallest of all the primates. "It is widely known that a reduced body size demands higher metabolic requirements. According to this biological principle, we have found genetic variants in the titi related with the metabolic rate and the regulation of body temperature, as well as different hormones and growth factors", said Dr. Kim Worley.

The analysis of the different genes of proteases of the titi by the group of Dr. López-Otín led to the discovery of a variation of the gene MMP19 that may affect the system that controls growth. This discovery is joined by others whose consequences may influence both in the reproductive features and in the immune response of these minute primates. "Apart from finding these variants", explains David Rodríguez, "we have seen a genomic mechanism, called retrotransposition, that seems to have notably influenced the evolution of the titi".

Carlos López-Otín relates these discoveries to one of the key goals of his groups. "The development of cancer is related to the number of cells that an individual has: the higher the number of cells, the higher the chance that one of them becomes a tumor", he explains. "The titi, being the primate with the fewest number of cells, probably has a relaxed set of antitumoral mechanisms in comparison to humans".

In turn, the group of Dr. Marqués-Bonet has identified the duplicated regions of the genome of the titi, and points out that "the results obtained by our group seem to be related with another distinctive feature of this primate: twin titis exchange cells while their are in the uterus of their mother". This characteristic is not naturally found in any other mammal, and, when it occurs, it leads to medical issues.

Another of the important aspects of this research has been the association of certain genetic variants with a particular reproductive feature of the titi. "In comparison to human beings, titis give birth to twins very frequently, which seems to be related to concrete variants of the gene WFIKKN1", indicated Dr. Worley. This gene may act as a sort of interruptor between multiple and unique births, although it is not the only gene involved. This discovery may be applied to research on multiple births in humans.