Healthy mice born to same-sex par­ents

China Daily (Hong Kong) - - FRONT PAGE - By ZHANG ZHIHAO zhangzhi­hao@chi­

Chi­nese sci­en­tists have pushed the boundaries of re­pro­duc­tive science by breed­ing healthy mice us­ing ge­netic ma­te­ri­als from same-sex par­ents, with­out the need for males to fer­til­ize eggs as re­quired for mam­mal re­pro­duc­tion.

The re­search can shed light on why mam­mals can only re­pro­duce sex­u­ally, as well as pro­vide a bet­ter un­der­stand­ing of and pos­si­ble cure for some forms of in­fer­til­ity and birth de­fects, sci­en­tists said. Such tech­niques might also be used to pre­serve crit­i­cally en­dan­gered an­i­mals that can­not find a mate.

Some hope this new work could lead to the pos­si­bil­ity that ho­mo­sex­ual cou­ples would be able to have their own bi­o­log­i­cal chil­dren, but such an ap­pli­ca­tion faces mon­u­men­tal tech­ni­cal and eth­i­cal ob­sta­cles that would be ex­tremely dif­fi­cult to over­come, the sci­en­tists said.

Us­ing gene edit­ing and stem cells, re­searchers from the In­sti­tute of Zool­ogy of the Chi­nese Academy of Sci­ences cre­ated 29 healthy mice pups born to pairs of fe­male mice. The pups lived to adult­hood and had ba­bies of their own, ac­cord­ing to the

study pub­lished on Thurs­day in the jour­nal Cell Stem Cell.

In 2004, sci­en­tists in Ja­pan pro­duced the first mice from two moth­ers us­ing com­plex ge­netic ma­nip­u­la­tions, but the mice that were born ex­hib­ited se­ri­ous birth de­fects, such as growth re­tar­da­tion and poor mo­tor skills.

The new study said it also marks the first time that pups from pairs of male mice were born. How­ever, most of them died soon af­ter birth, with just two out of the 12 male pups sur­viv­ing more than 48 hours. Sci­en­tists are plan­ning to im­prove the process so that the male mice can live to adult­hood.

Zhou Qi, the pa­per’s co-se­nior au­thor and the direc­tor of the in­sti­tute, said in a news re­lease on Thurs­day that the main pur­pose of the re­search was to probe why mam­mals can only un­dergo sex­ual re­pro­duc­tion.

In the nat­u­ral world, cer­tain types of rep­tiles, am­phib­ians and fish can re­pro­duce with­out two par­ents of the op­po­site sex, but this is ex­tremely chal­leng­ing for mam­mals, even with ad­vanced science, he said.

Same-sex re­pro­duc­tion is dif­fi­cult for mam­mals due to a mech­a­nism called ge­nomic im­print­ing, whereby cer­tain genes are turned on or off de­pend­ing on whether they come from the mother or fa­ther, Teresa Holm, a re­searcher from New Zealand’s Uni­ver­sity of Auck­land, said in the study’s re­view. The re­view was pub­lished on Scimex, an on­line science news por­tal, by the Aus­tralian Science Me­dia Cen­tre.

If these im­prints and the pat­tern they form are not tightly con­trolled, it can be cat­a­strophic for the em­bryo, re­sult­ing in birth de­fects or death, Holm said.

The study demon­strates how this bar­rier could be over­come by delet­ing prob­lem­atic im­print­ing from hap­loid em­bry­onic stem cells, which have just a sin­gle set of chro­mo­somes and are cul­tured from sperm or egg cells. These edited stem cells are then in­jected into eggs from the other par­ent.

“The ma­jor im­pact of this work fur­ther ex­pands our fun­da­men­tal un­der­stand­ing of how im­print­ing op­er­ates in mam­mals and how it acts as a bar­rier to uni­parental re­pro­duc­tion,” Holm added.

In the long term, the knowl­edge may help in­fer­tile cou­ples due to im­print­ing is­sues, and even lead to the de­vel­op­ment of ways for same-sex cou­ples to re­pro­duce healthy chil­dren of their own, she said.

But Holm stressed that the cur­rent work is only ap­pli­ca­ble to mice, and fu­ture ap­pli­ca­tions in hu­mans still carry sig­nif­i­cant tech­ni­cal, eth­i­cal and safety con­cerns.

Li Wei, an­other of the study’s au­thors, said in a news re­lease that the Chi­nese team is hop­ing to ex­plore these tech­niques in other re­search an­i­mals in the fu­ture, such as in non­hu­man pri­mates.

How­ever, Li said ma­jor tech­ni­cal ob­sta­cles re­main, such as mod­i­fy­ing im­printed genes of more ge­net­i­cally com­plex or­gan­isms and con­cerns for the off­spring’s health af­ter birth.

Robert Nor­man, a pro­fes­sor of re­pro­duc­tive medicine at the Uni­ver­sity of Ade­laide in Aus­tralia, said in the re­view that the new tech­nique might help save crit­i­cally en­dan­gered an­i­mal species, but there are far too many un­cer­tain­ties for it to be used in hu­man re­pro­duc­tion.

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