Ayam Lokal Tahan Banting

Rabu, 23 Januari 2008 | 14:21 WIB

TEMPO Interaktif, Jakarta:

Ayam yang satu ini memang istimewa. Bulu, kaki, jengger, paruh, dan lidahnya berwarna hitam pekat. Bahkan daging dan darahnya pun hitam. Karena itu, ayam cemani dipercaya memiliki kekuatan mistis. Ternyata ayam dari Jawa Tengah ini juga punya kekuatan lain, yaitu tahan terhadap serangan virus flu burung.

Begitulah hasil penelitian Sri Sulandari dan M. Syamsul Arifin Zein, dua peneliti genetika zoologi di Pusat Penelitian Biologi, Lembaga Ilmu Pengetahuan Indonesia (LIPI). Mereka telah meneliti sampel darah dari 15 galur ayam lokal Indonesia dan ayam kampung yang selamat dari wabah flu burung di beberapa daerah.

Hasil analisis terhadap gen Mx terhadap populasi ayam Indonesia itu menunjukkan ayam cemani memiliki resistensi terhadap virus flu burung yang paling tinggi, 0,89 persen, dibanding galur ayam lainnya. Adapun ayam kapas memiliki resistensi terendah, hanya 0,35 persen.

Namun, bukan berarti semua ayam cemani resisten terhadap virus itu. Zein menekankan bahwa hasil penelitian ini tidak berlaku untuk semua populasi ayam cemani yang tidak ditelitinya. "Dalam penelitian ini, ayam cemani yang kami ambil darahnya berasal dari Kedu, Temanggung," kata Zein. "Riset menunjukkan 88 persen dari populasi cemani yang diteliti memiliki protein yang resisten virus flu burung. Kalau ada populasi ayam cemani lain yang bertentangan dengan penelitian ini, bisa saja. Kebetulan yang kita ambil di pusat Cemani, kondisinya bagus."

Ketahanan ayam cemani itu ternyata ditentukan oleh gen Mx. Para ilmuwan telah mengetahui fungsi gen itu sebagai penentu kemampuan ayam untuk resisten atau justru rentan terhadap serangan virus avian influenza. Gen ini ditemukan pada beberapa hewan vertebrata, seperti mamalia, unggas, dan ikan, bahkan beberapa avertebrata.

Mutasi pada gen yang berada dalam kromosom 1 dengan 14 exon itulah yang menentukan resistensi ayam terhadap flu burung. Mutasi alel A (genotipe AA) menjadi G (genotipe GG) pada nukleotida ke-1.892 pada exon ke-13 itu menyebabkan adanya perubahan asam amino dari serin (AGT) menjadi asparagin (AAT).

Perubahan alel A menjadi G ini membuat unggas rentan terhadap flu burung, karena membentuk protein yang seharusnya mampu melawan. Alel A resisten terhadap serangan virus avian influenza, alel G rentan terhadap serangan virus itu, sedangkan alel R (genotipe AG) bisa resisten tapi juga bisa rentan.

Sulandari mengatakan hasil analisis terhadap fenomena mutasi alel G/A terhadap populasi ayam lokal di Indonesia itu menunjukkan bahwa ketahanan ayam lokal Indonesia terhadap virus tersebut cukup tinggi. "Rata-rata frekuensi alel A di atas 50 persen itu bagus," katanya. "Kalau kurang dari itu rentan karena, dalam populasinya, umumnya (ayam) memiliki alel GG, sedangkan alel AA tahan banting."

Selain cemani, ayam merawang dari Kepulauan Bangka Belitung yang diteliti dalam riset sejak 2007 itu menunjukkan frekuensi alel A yang tinggi. Begitu pula ayam pelung yang mereka teliti dari daerah Ciamis.

Sri Sulandari menyatakan penelitian gen Mx dari 877 sampel ini juga menghasilkan temuan penting, yaitu ayam yang selamat dari wabah avian influenza di Banten, Lampung, dan Sumatera Utara memiliki daya resisten cukup tinggi. "Frekuensi alel A ayam kampung di daerah itu cukup tinggi, antara 0,60 dan 0,73," katanya.

Ayam hutan merah, yang merupakan nenek moyang dari ayam domestikasi, mempunyai frekuensi alel A 0,49 persen. Angka yang diperlihatkan ini masih dalam kisaran frekuensi alel A yang dimiliki ayam lokal Indonesia. "Selain ayam hutan hijau (Gallus varius), secara keseluruhan ayam-ayam yang digunakan dalam penelitian ini, ayam kampung dan ayam hutan merah, mempunyai frekuensi alel resisten cukup tinggi," ujarnya.

Faktor daya tahan terhadap serangan flu burung ini, kata Zein, bisa dimanfaatkan dalam program pemuliaan. Secara alamiah, ayam dengan alel genotipe AA mampu melakukan perlawanan terhadap serangan flu burung. "Ayam dengan alel A akan memiliki keturunan dengan alel A pula, maka data ini penting sekali untuk keperluan breeding," ujarnya. "Kami tidak terlalu concern dengan ayam cemani resisten atau tidak, tapi sistem ini bisa digunakan untuk breeding."

Zein menyatakan bahwa dengan sistem ini dia bisa menciptakan populasi ayam yang 100 persen tahan serangan virus mematikan itu. Bila ada orang yang ingin membuat peternakan ayam kampung, bisa bekerja sama dengan laboratorium dengan menyeleksi induk sehingga menghasilkan keturunan yang tahan virus. "Yang tahan dikembangkan, yang jelek dibuang," katanya.

Cara membuat keturunan tahan virus flu burung sebenarnya sederhana, dengan memeriksa gen Mx ayam yang hendak dikembangbiakkan. "Misalnya kita ambil ayam jantan dan betina beralel AA," ujarnya. "Kalau beralel AA bertemu dengan AA, anaknya pasti AA. Kalau AG dengan AG, kadang alel bergenotipe GG keluar."

Selain menciptakan generasi ayam tahan flu burung, penelitian ini bisa digunakan bagi pengambil kebijakan dalam mengatasi wabah flu burung. "Setelah serangan (flu burung), kita maunya menjelaskan kepada pemerintah bahwa yang hidup itu adalah yang tahan, tapi akhirnya dibunuh," kata Zein. "Jadi yang nggak resisten mati karena penyakit, tapi yang resisten mati dibunuh."

Langkah membumihanguskan peternakan yang terkena wabah itu, kata Zein, kurang tepat. Jika kebijakan depopulasi--membunuh semua unggas yang hidup berbagi tempat dengan unggas mati--itu diteruskan, genetic resource Indonesia terancam bahaya. "Kalau ayam yang tahan virus dibunuh, sumber daya genetik kita habis, akhirnya kita punya ayam berkualitas lembek," ujarnya. "Sehingga bisa terjadi seperti kasus kedelai, bergantung pada Amerika terus. Kita tidak menanam, impor mahal."

TJANDRA DEWI

from here

Mixing Mammals

By outfitting mice with a chunk of DNA that directs wing development in bats, scientists have created rodents with abnormally long forelimbs, mimicking one of the steps in the evolution of the bat wing. Their work gives weight to the idea that variations in how genes are controlled, and not just mutations in the coding regions of genes, are a driving force in evolution.

The slightly longer forelimbs of the transgenic mice "make them more batlike," says Nipam Patel, a professor of molecular and cell biology and integrative biology at the University of California, Berkeley, who was not involved in the work. "It seems like a subtle difference, but evolution works by these subtle differences."

The researchers focused on a gene, Prx1, that plays a part in the elongation of limb bones in mammals. The gene's expression is regulated by another sequence of DNA, called a Prx1 enhancer. To investigate how the enhancer shapes limb development, Richard Behringer, a professor of molecular genetics at the University of Texas MD Anderson Cancer Center, and his colleagues around the country put the bat version of the Prx1 enhancer into mice so that it controlled the mouse Prx1 gene. These transgenic animals developed forelimbs that were on average 6 percent longer than normal by the time they were born. It was a significant difference, although "the mice look like mice," Behringer says. "They're not going to fly out of the cage." The researchers report their work in the latest issue of Genes and Development.

To have any chance of flying, mice would have to develop very different forelimbs, like those of bats, which are longer and have membranes stretched between the bones. Behringer says that he'd like to try replacing the limb enhancers in mice with those from other animals, such as whales or wallabies.

Charles Darwin contemplated the evolution of different kinds of limbs in On the Origin of Species. Starting with a basic limb pattern, "successive slight modifications," he wrote, eventually produce the various mammal limbs we see today: human hands, bat wings, whale fins.

"We think what we've done is made one of those slight modifications," Behringer says. "Maybe during evolution you'd have a lot of those and the limb would get a lot longer, and maybe some of the tissue would be retained between digits, ultimately leading to the structures that would allow a bat to fly."

"It's a very nice demonstration of something that people have been suspecting now for some time: that regulatory sequences rather than changes in protein sequences sort of drive evolution," says Susan Mackem, who heads the Developmental Biology Unit at the National Cancer Institute's Center for Cancer Research. Mackem was not involved in Behringer's research.

Behringer's team also found something unexpected. When the researchers created mutant mice that lacked the mouse Prx1 enhancer, the animals developed forelegs of a normal length. That suggests that more than one enhancer controls the expression of the Prx-1 gene in mice, ensuring what Behringer calls a "regulatory redundancy."

"As long as there is one copy to do the work, the other copy can be creative," says Ann Burke, an associate professor of biology at Wesleyan University.

from here

US approves animal clones as food

By Richard Black
Environment correspondent, BBC News website

The US government has given the green light to the production and marketing of foods derived from cloned animals.

After six years of study, the Food and Drug Administration (FDA) ruled that meat and milk from cloned pigs, cattle and goats and their offspring is safe.

Lack of data meant the agency could not reach a decision on sheep products.

The FDA does not expect to see a lot of products from cloned animals being sold now, because of cost. It expects clones would first be used for breeding.

The agency released almost identical draft conclusions in December 2006. Since then, new scientific information has strengthened its central view.

Just because something was created in a lab, doesn't mean we should have to eat it Senator Barbara Mikulski

"After reviewing additional data and the public comments in the intervening year since the release of our draft documents on cloning, we conclude that meat and milk from cattle, swine, and goat clones are as safe as the food we eat every day," said Stephen Sundlof, director of the FDA's Center for Food Safety and Applied Nutrition.

The FDA will not require food derived from cloned animals to be labelled as such.

Low confidence

The agency was criticised by activist groups and by US politicians who were not convinced that enough scientific data was available to justify a decision.

"The FDA has acted recklessly, and I am profoundly disappointed in their rush to approve cloned foods," said Maryland Senator Barbara Mikulski, co-sponsor of a bill amendment passed by the US Senate which asked the FDA not to rule until further research was available.

"Just because something was created in a lab, doesn't mean we should have to eat it."

Her criticisms were echoed by Andrew Kimbrell of the Center for Food Safety, a prominent US pressure group.

"The FDA's bull-headed action disregards the will of the public and the Senate and opens a literal Pandora's Box," he said.

Observers do not anticipate a rush to market cloned milk and meat

"The FDA based their decision on an incomplete and flawed review that relies on studies supplied by cloning companies that want to force cloning technology on American consumers."

A survey in 2005 by the Pew Charitable Trusts found that two-thirds of US consumers were "uncomfortable" with animal cloning; nearly half believed food from clones would be unsafe to eat.

Some US food companies have indicated they do not plan to stock products derived from cloned animals.

But Smithfields, which claims to be the biggest producer of pigs and pork products in the country, left the door open to a change of tack, saying it would "continue to monitor further scientific research on this technology" and was committed to improving its products "through careful selective breeding and genetic research".

Breeders themselves expressed their approval.

"The biotechnology industry applauds the FDA for its comprehensive scientific review of this new assisted reproductive technology," said Jim Greenwood, president and CEO of the Biotechnology Industry Organization (Bio), which represents companies and institutions in the biotech field.

"Cloning... can effectively help livestock producers deliver what consumers want: high-quality, safe, abundant and nutritious foods in a consistent manner."

Delayed action

US authorities do not expect to see a wave of products derived from cloned animals on the shelves immediately.

Creating a clone is far more expensive than breeding animals conventionally. The US Department of Agriculture (USDA) believes it is more likely that companies will produce clones with "desirable" traits, breed them, and bring products from the offspring into the food chain.

The USDA is asking companies not to market products immediately, but to continue observing the moratorium they agreed to in 2001 when the FDA began its deliberations.

"USDA encourages the cloning industry continue its voluntary moratorium for a sufficient period of time to prepare so that a smooth and seamless transition into the marketplace can occur," it said in a statement.

The US developments will be watched closely in Europe, where evaulation of cloned animals is at an earlier stage.

Last week the European Food Safety Authority (Efsa) initiated a public consultation on its draft guidance.

The draft concluded, among other things, that:

• foods from cloned pigs and cattle are essentially identical to those from conventionally bred animals
• animal cloning is unlikely to have environmental impacts
• there are health and welfare issues, but these are likely to diminish as technology progresses

The EU has indicated that if products from cloned animals were approved, they would have to be labelled.

This contrasts directly with the US position, opening up the possibility of trade disputes similar to the lengthy and costly row between the EU and US over genetically modified foods.

Richard.Black-INTERNET@bbc.co.uk

From here