viernes, 3 de junio de 2005

La orientación sexual en la mosca de la fruta, tomo I

Es difícil hablar de esto sin remitir a la fuente. Y como sé que es engorroso -y aburrido- pasar todas las aduanas para llegar al texto, transcribo el original. Por esta vez, al menos. Otras veces habrá que aburrirse, qué remedio.

El artículo de hoy en The New York Times se titula For Fruit Flies, Gene Shift Tilts Sex Orientation y lo redactó Elisabeth Rosenthal, del International Herald Tribune.

Se trata de la divulgación de estilo de experimentos sobre la sexualidad de la mosca de la fruta.
When the genetically altered fruit fly was released into the observation chamber, it did what these breeders par excellence tend to do. It pursued a waiting virgin female. It gently tapped the girl with its leg, played her a song (using wings as instruments) and, only then, dared to lick her - all part of standard fruit fly seduction.

The observing scientist looked with disbelief at the show, for the suitor in this case was not a male, but a female that researchers had artificially endowed with a single male-type gene.

That one gene, the researchers are announcing today in the journal Cell, is apparently by itself enough to create patterns of sexual behavior - a kind of master sexual gene that normally exists in two distinct male and female variants.

In a series of experiments, the researchers found that females given the male variant of the gene acted exactly like males in courtship, madly pursuing other females. Males that were artificially given the female version of the gene became more passive and turned their sexual attention to other males.

"We have shown that a single gene in the fruit fly is sufficient to determine all aspects of the flies' sexual orientation and behavior," said the paper's lead author, Dr. Barry Dickson, senior scientist at the Institute of Molecular Biotechnology at the Austrian Academy of Sciences in Vienna. "It's very surprising."

"What it tells us is that instinctive behaviors can be specified by genetic programs, just like the morphologic development of an organ or a nose."

The results are certain to prove influential in debates about whether genes or environment determine who we are, how we act and, especially, our sexual orientation, although it is not clear now if there is a similar master sexual gene for humans.

Still, experts said they were both awed and shocked by the findings. "The results are so clean and compelling, the whole field of the genetic roots of behavior is moved forward tremendously by this work," said Dr. Michael Weiss, chairman of the department of biochemistry at Case Western Reserve University. "Hopefully this will take the discussion about sexual preferences out of the realm of morality and put it in the realm of science."

He added: "I never chose to be heterosexual; it just happened. But humans are complicated. With the flies we can see in a simple and elegant way how a gene can influence and determine behavior."

The finding supports scientific evidence accumulating over the past decade that sexual orientation may be innately programmed into the brains of men and women. Equally intriguing, the researchers say, is the possibility that a number of behaviors - hitting back when feeling threatened, fleeing when scared or laughing when amused - may also be programmed into human brains, a product of genetic heritage.

"This is a first - a superb demonstration that a single gene can serve as a switch for complex behaviors," said Dr. Gero Miesenboeck, a professor of cell biology at Yale.

Dr. Dickson, the lead author, said he ran into the laboratory when an assistant called him on a Sunday night with the results. "This really makes you think about how much of our behavior, perhaps especially sexual behaviors, has a strong genetic component," he said.

All the researchers cautioned that any of these wired behaviors set by master genes will probably be modified by experience. Though male fruit flies are programmed to pursue females, Dr. Dickson said, those that are frequently rejected over time become less aggressive in their mating behavior.

When a normal male fruit fly is introduced to a virgin female, they almost immediately begin foreplay and then copulate for 20 minutes. In fact, Dr. Dickson and his co-author, Dr. Ebru Demir of the Institute of Molecular Biotechnology, specifically chose to look for the genetic basis of fly sexual behavior precisely because it seemed so strong and instinctive and, therefore, predictable.

Scientists have known for several years that the master sexual gene, known as fru, was central to mating, coordinating a network of neurons that were involved in the male fly's courtship ritual. Last year, Dr. Bruce Baker of Stanford University discovered that the mating circuit controlled by the gene involved 60 nerve cells and that if any of these were damaged or destroyed by the scientists, the animal could not mate properly. Both male and female flies have the same genetic material as well as the neural circuitry required for the mating ritual, but different parts of the genes are turned on in the two sexes. But no one dreamed that simply activating the normally dormant male portion of the gene in a female fly could cause a genetic female to display the whole elaborate panoply of male fruit fly foreplay.

¿Llegaron hasta aquí? Bien. Habrán visto que, para poder leer de corrido, la cuestión es admitir algunos puntos.

1. Que hay signos materiales y corpóreos que indican el sexo. Unos para lo masculino y otros para lo femenino. Concretamente, según dicen aquí de la mosca de la fruta, una especie de gen maestro con dos variantes: masculina y femenina.
2. Este gen maestro, conocido por el nombre de fru, y presente en los ejemplares de cada sexo en sus respectivas variantes, influye y determina la conducta sexual específica de cada ejemplar según su respectivo sexo.
3. Si se modifica este gen -tal como por ejemplo los investigadores lo 'tocaron' artificialmente-, las conductas sexuales específicas del sexo respectivo cambian.
4. Finalmente, tal como se afirma, ambos sexos tienen el mismo material genético, y el mismo circuito neuronal requerido para los encuentros sexuales. Simplemente, una parte de ello se activa en los ejemplares masculinos y otra en los femeninos. Si se daña o destruye algunas células, o se activan las partes normalmente dormidas del sexo opuesto, sus conductas sexuales varían.

Ahora bien, en medio de esta explicación divulgadora sobre el experimento, se dicen varias otras cosas. A saber,

1. Que todo esto les parece sorprendente a los científicos.
2. Que -y se dice con cierta insistencia en el artículo- aunque no se sabe si esto es así en los humanos como en las moscas de la fruta, lo que se dice de ellas se aplica a ellos, sin más trámite.
3. Que los genes determinan nuestras conductas, incluso nuestras conductas complejas, por ejemplo nuestra 'orientación' sexual.
4. "Hopefully this will take the discussion about sexual preferences out of the realm of morality and put it in the realm of science", es decir, repito, pese a que no se puede afirmar lo mismo para los humanos, el supuesto descubrimiento sacará la discusión acerca de las 'preferencias' sexuales del ámbito moral y lo pondrá en el ámbito que se considera el debido: el de la ciencia.
5. Finalmente, aunque hay más afirmaciones de este tipo: "I never chose to be heterosexual; it just happened. But humans are complicated. With the flies we can see in a simple and elegant way how a gene can influence and determine behavior." Otra vez: 'it just happened', aunque 'humans are complicated'.

(Ay, con esa cosa de haberse robado el adjetivo 'elegante'...)

Por hoy, siendo viernes -y fiesta grande del Sagrado Corazón de Jesús- se me hace suficiente.

Pero, nada me librará de una segunda parte. Esto no es todo.

Mucho más breve, claro. Eso espero.