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Cellular Cowboys: How the Cell Rounds Up Chromosomes Before Dividing

first_imgTwo cancer researchers from UC San Diego describe mitosis (cell division) in the Mar. 4 issue of Nature.1  Pulling together the latest findings about this elaborate and important process, they begin by describing the puzzle that the cell needs to solve:At the beginning of mitosis, the process of cell division, chromosomes are organized randomly – like jigsaw puzzle pieces spread out on the floor.  Their constituent two ‘sister chromatids’, each of which contains one of the two identical DNA molecules produced by replication, must be oriented such that they will be pulled in opposite directions into the two newly forming cells.  Like a jigsaw, the solution for correctly orienting all chromosomes comes partly through trial and error.  Mechanisms must exist to eliminate wrong configurations while selecting the right ones.In the article, they describe how cables (microtubules) connect to handles (kinetochores) on the chromosomes and start pulling them in opposite directions.  Another enzyme dissolves the molecular “glue” in the centrosomes that hold the sister chromatids together, so that the opposite poles of the spindle can pull them apart into the daughter cells.    A newly-described “highly-conserved enzyme” (i.e., identical in yeast and vertebrates), named Aurora B kinase, somehow finds chromosomes that lack an attachment to the other pole of the spindle, and fixes them.  Apparently this enzyme is able to identify chromosomes that are incorrectly lassoed to the same pole (syntelic attachment) and therefore are not under tension.  Only when there is tension on each chromosome, pulling the sister chromatids toward opposite poles, will the process continue.  “Finding out how Aurora B identifies and corrects them is an obvious next step,” the authors say.Ian M. Cheeseman and Arshad Desai, “Cell division: Feeling tense enough?”, Nature 428, 32 – 33 (04 March 2004); doi:10.1038/428032b.First of all, think of how many parts are involved in this process.  Then realize that without high fidelity duplication and segregation during cell division, an organism would be subject to cancer, genetic disease or death.  Furthermore, any alleged evolution would quickly come to a grinding halt, because natural selection is highly dependent on accurate replication for selected traits to be preserved.    To visualize what goes on in mitosis, think of the following analogy.  (Analogies, though never precise, and inadequate as proofs, can help make complex processes approachable.)  Let’s head out West and picture a team of cowboys who need to split a herd of cattle for market.  The cattle in our hypothetical herd all have identical twins that are yoked together.  They are wandering aimlessly in a corral, and two teams of cowboys are standing at opposite ends of the corral with lassos in hand.  On cue, the corral fence (the nuclear membrane) drops.  The cowboys immediately go into action, lassoing every cow in sight.    Their goal is to split the herd into identical halves.  To accomplish this, each team has to catch one of each pair: Bob, on the north team, lassos one of the twins, and Joe, on the south team, lassos the other.  As soon as a cow is caught, the cowboy starts pulling.  Sometimes, however, two guys on the same team catch both twins.  That’s when wrangler Chuck (Aurora B kinase) rides through the herd, looking at ropes that aren’t taut, indicating pairs hitched to the same team.  Chuck removes one of the ropes and lets the other team lasso the twin.  As the ropers keep applying tension, the boss makes sure all the pairs are lined up, each with one rope pulling a cow north and another rope pulling its twin south.  Then another wrangler breaks the yokes, and the cowboys wind in their ropes, pulling their half of the herd into the new north and south corrals.    The difference in cells is that they don’t have sentient cowboys with eyes and ears doing the work by using their brains and roping skills.  Instead, cables called microtubules extend outward blindly at random from the spindle poles, looking for attachment points on the kinetochores at the middle of the chromosomes.  Tension is applied by molecular motors (see 02/25/2003 headline), like winches, that pull the chromatids into the daughter cells.  How can a cell make sure one and only one cable gets attached to each chromatid?  This is awesome.  Consider also that all the machinery, all the ropes, all the winches, all the corrals, all the procedures and everything else is produced by the DNA in the chromosomes, as if the cattle were the master controller and supplier for the cowboys!  For photomicrographs of mitosis, see the illustrations at the Florida State University and the University of Maryland websites.    Mitosis is a coordinated team project that is done exactly right by the cell every time it divides.  Mistakes by cowboys might mean a lawsuit or the loss of business, but in the cell, a mistake can mean death.  The process is amazing enough as described, but then the authors throw in “the rest of the story” to boggle Darwinian minds beyond all hope of recovery.  What they described was for yeast – a “primitive” form of life.  What happens in vertebrates, like us humans?  Get ready:In contrast to budding yeast, kinetochores of other eukaryotes bind multiple microtubules (about 20 in humans).  These larger kinetochores must coordinate all these microtubules and also deal with incorrect attachments in which microtubules from opposite spindle poles connect to a single kinetochore (termed ‘merotely’).  Another study, in this month’s Nature Cell Biology, found that Aurora B does not merely detach syntelic kinetochores from microtubules in vertebrates – it orchestrates the coordinated disassembly of all the microtubules that are bound to each kinetochore, so that the syntelically oriented chromosomes move towards the spindle poles before they are bi-oriented.    Although sister kinetochore geometry seems to be dispensable in budding yeasts with their single-microtubule-connected kinetochores, it could contribute to reducing merotely, as implied by the conservation of this aspect of chromosome architecture throughout eukaryotic evolution.  Tackling the extra dimension that the multiplicity of microtubule-binding sites at kinetochores introduces will undoubtedly be another brain-teaser – and a particularly important one, too, because the loss of a single chromosome can be lethal, and aberrant numbers of chromosomes can contribute to birth defects and cancer.Isn’t evolution wonderful.  It blindly found a way to solve multi-dimensional jigsaw puzzles correctly every time, and hung onto its invention for millions of years.  It started a successful cattle ranching business, employing blind cowboys.  Its advertisement boasts, “Satisfying customers since 2 billion years B.C.”  Would you trust such hype?    One last thought.  Remember the 02/13/2003 headline last year?  It reported that meiosis (cell division for sexual reproduction) is even “much more complex” than mitosis, but there was no evidence it had evolved from the “simpler” process of mitosis.  These are bad days to work for Charlie on the Lazy E Ranch.  Better quit the outfit while you can and join up with the Boss who knows the business.(Visited 9 times, 1 visits today)FacebookTwitterPinterestSave分享0last_img read more

Ntataise helps to give children the best start

first_imgThe benefits of early childhood development include greater physical, social, emotional and cognitive development and can have a telling effect on the child’s development into adulthood. (Image: Ntataise)Across the world people are waking up to the importance of making sure that the children in their care are equipped as best as possible, as soon as possible through early childhood development (ECD).ECD can mean closing the gaps between different classes and working to fight inequality in the long run by levelling the playing field. It can ensure that no class has an advantage over the next as a result of their upbringing.Ntataise, meaning “to lead a young child by the hand”, looks to use the benefits of ECD to foster a generation of children who are given the best possible start in life. Founded in 1980, the organisation was created with the aim of helping women living in underprivileged areas in Free State to establish their own ECD programmes.Since inception, the organisation has spread its influence from Free State to all corners of the country. It has been dedicated to improving the development of young children for the better part of the past three-and-a-half decades.Jane Evans, the founder and director of Ntataise, says the organisation is “one of the oldest and, I also like to think, one of the leading mental health organisations that works with communities in developing early childhood development for children who would otherwise not have access to this early intervention”.According to a report compiled by Ntataise, the organisation has empowered thousands of women across the country who have used the skills and knowledge acquired to benefit some 500 000 children. They have also helped to improve the standard of the programmes on offer nationwide. ECD can mean closing the gaps between different classes and working to fight inequality in the long run by levelling the playing field.NTATAISE NETWORKChief among the organisation’s successes is its ever-growing network, which includes some of the country’s leading ECD training organisations. The network has been in the making for more than 20 years and continues to swell its numbers as more and more people become aware of what ECD can offer.Today, the Ntataise network consists of 18 ECD programmes, spreading its influence to seven of South Africa’s nine provinces. Members of the network have access to:Accredited training programmes;Resources and learning materials;Moderation and assessment systems;Programme development; and,Mentoring, support and capacity building programmes for facilitators of ECD programmes.Angelina Mashio, the director of Siyathuthuka Nursery School Project, said the project had been “getting assistance from Ntataise since 2002”.“We also got training and more development, especially as new directors of organisations and programmes that offer this training,” she said. “Ntataise tries its best to improve our working conditions by capacitating us and developing our trainers.”The strength of the Ntataise programme lies in the fact that, through the network, it receives constant feedback from many sources. This allows it to continuously improve its programmes and ensure they are implemented properly and remain relevant.Its reports indicate that, through its network, Ntataise reaches about 3 000 practitioners and more than 100 000 children countrywide each year.GET INVOLVEDEvans believes it is vital that the public, the government and ECD organisations such as Ntataise work together to ensure the poorer sectors of society aren’t left behind.The sustainability of Ntataise’s programmes and its expansive network is dependent on the generosity of people who believe in the cause.To help ensure its longevity, visit the Ntataise website for more information regarding the part you can play in helping it deliver ECD programmes in future.last_img read more

Farm Bureau policy committee begins work

first_imgShare Facebook Twitter Google + LinkedIn Pinterest  Leave a CommentTwenty Ohio Farm Bureau leaders are serving on the Ohio Farm Bureau Federation Policy Development Committee. The committee collects and organizes public policy recommendations from county Farm Bureaus and presents the final policy suggestions to be voted on by Ohio Farm Bureau’s delegates during the state annual meeting in December.  In its initial session, the committee heard from government leaders, subject matter experts and Farm Bureau staff on topics such as the shortage of large animal veterinarians, Ohio’s fertilizer guidelines, managing nutrient loss, education policy, infrastructure funding, engagement in the Ohio Power Siting evaluation process, deer and wildlife management, abandoned railways and trails, land conservation programs and industrial hemp. The policy committee consists of 10 members from Ohio Farm Bureau’s board of trustees and 10 representatives of county Farm Bureaus.   The committee is chaired by Ohio Farm Bureau First Vice President Bill Patterson of Chesterland and includes OFBF President Frank Burkett of Massillon and Treasurer Cy Prettyman of New Bloomington. State trustees on the committee are Roger Baker of Wooster, Nathan Brown of Hillsboro, Paul Davidson of Newark, Bill Waddle of Springfield, Al Miller of Marietta, Lane Osswald of Eldorado and Kyle Smith of South Vienna.County Farm Bureau representatives are Adele Flynn of Lorain County, John Grafton of Jefferson County, Rebekah Headings of Madison County, Rachel Heimerl of Licking County, Kent McGovern of Ashland County, Jamie Pursell of Seneca County, Jamey Rauch of Washington County,  Robert Sinn of Paulding County, Robert Suver of Clark County and Cindy Wilson of Morgan County. This is a news release for use by journalists. Questions should be directed to Joe Cornely, 614-246-8230.  Leave a Commentlast_img read more

Discover the creatures of the oceans

first_img SharePrint RelatedFrom Sketch to Souvenir: the artist behind Hidden CreaturesJune 19, 2018In “News”Uncover a new world of Hidden CreaturesJune 5, 2018In “News”The world wide search for Hidden Creatures continuesJuly 10, 2018In “News” Centuries of exploring uncharted waters resulted in legends describing fantastic creatures, almost too strange to be true. Though the ocean may be vast, there’s still time to search for the giant Kraken, the elusive Hippocamp, and the mysterious Mermaid. Now it’s your turn to confirm the tales! Now through July 25, find geocaches or attend events to find Hidden Creatures earning up to 13 new souvenirs.View your progressShare with your Friends:Morelast_img

Heads Up: The IDF Is Live-Blogging Its Attack On Hamas

first_imgAfter providing the background info, the account announced that “the IDF has embarked on Operation Pillar of Defense,” insisting that “all options are on the table,” including a ground operation “if necessary.”The next tweet shared this intense, 10-second aerial video of a pinpoint strike on a vehicle reportedly carrying Ahmed Jabari, head of what the IDF calls the “Hamas Military Wing.” This operation has driven Egypt to call for an emergency meeting of the UN security council. Ahram Online is reporting that Egypt’s newly appointed ambassador to Israel, Atef Mohamed Salem, has been recalled by President Mohamed Morsi.It’s a strange new world.We’ve reached out to Twitter for comment on how this whole thing looks from their perspective, and we’ll update the post if we hear back. Tags:#War jon mitchell A Comprehensive Guide to a Content Audit This carefully planned social media campaign around a military operation is an amazing kind of PR that we at ReadWrite don’t know of a precedent for. If you do, please share it with us, and we’ll be glad to update with more info.UPDATE 12:51 Pacific: My friend Eugene has pointed me to the Twitter feed of the Kenya Defense Forces (@kdfinfo), which has posted ongoing updates about military campaigns. It’s surely an interesting stream of information, but it’s far from the cross-media PR war machine the IDF is running right now.The Other Side Of The StoryThe Twitter account @AlqassamBrigade representing Hamas-affiliated brigades in Palestine took to Twitter to respond to the IDF campaign. It continues to report on the operation as well as retaliatory Hamas attacks.As he is beloved for doing, Andy Carvin is curating all sides of the story by retweeting reports from the ground on both the Israeli and Palestinian side. We’ve never seen anything quite like this. The verified social media accounts of the Israeli Defense Forces are providing live updates on a concerted military effort against Hamas. Using the hashtag #PillarOfDefense, the verified Twitter account @IDFSpokesperson is posting ominous messages, headline-style updates, and YouTube videos of strikes.It’s brilliant in its way. By controlling the messaging so tightly, the IDF ensures that the media coverage of the operation is framed the way Israel wants it. Why dig deeper when the information is so carefully presented right there? That’s a rhetorical question, of course. The PR move here is as devastating as the operation.The stream of tweets began with background information on the operation, explaining that Operation Pillar of Defense is in retaliation against Hamas rocket attacks.center_img Facebook is Becoming Less Personal and More Pro… The Dos and Don’ts of Brand Awareness Videos Immediately following that post, the IDF followed up with a blog post profiling Jabari. Jabari was in charge of the well-known operation that captured Israeli soldier Gilad Shalit in 2006 outside of the Gaza Strip. Jabari personally escorted Shalit to the Rafah Crossing with Egypt when Shalit was released in a prisoner exchange.The IDF then offered this statement in an image engineered to go viral:The IDF is also posting maps and other images to an official Flickr account.And in response to the operation, retaliatory strikes have already begun. Related Posts Guide to Performing Bulk Email Verificationlast_img read more