 |
|
Researchers discover mechanism that prevents two species from reproducing
October 27, 2009Cornell researchers have discovered a genetic mechanism in fruit flies that prevents two closely related species from reproducing, a finding that offers clues to how species evolve.
When two populations of a species become geographically isolated from each other, their genes diverge from one another over time.
Eventually, when a male from one group mates with a female from the other group, the offspring will die or be born sterile, as crosses between horses and donkeys produce sterile mules. At this point, they have become two distinct species.
Now, Cornell researchers report in the October issue of Public Library of Science Biology (Vol. 7, No. 10) that rapidly evolving "junk" DNA may create incompatibilities between two related species, preventing them from reproducing. In this case, the researchers studied crosses between closely related fruit flies, Drosophila melanogaster and D. simulans. Nearly 100 years ago, scientists discovered that when male D. melanogasters mate with female D. simulans, normal males survive, but the female embryos die.
"It has remained an unsolved problem," said Patrick Ferree, the paper's lead author and a postdoctoral researcher in the lab of co-author Daniel Barbash, an assistant professor of molecular biology and genetics. "The question is, what are the elements that are killing these female hybrids and how are they doing that?"
The researchers found that the female hybrid embryos died very early in development. In most species, when the male's sperm (carrying either an X or Y chromosome) fertilizes the female's egg (containing an X chromosome), a new cell forms with a single nucleus containing a sex chromosome from each parent. If the offspring inherits its father's X chromosome, it becomes female; if it inherits a Y chromosome, it becomes male. Ferree and Barbash found that a unique segment of DNA in the father's X chromosome leads to embryo death of hybrid females.
The segment of DNA was found in the chromosome's heterochromatin, a densely packed region of highly repetitive sequences of junk DNA near the chromosome's center.
During the embryo's initial divisions, the researchers found, a specific segment of heterochromatin gets "sticky" and halts the process, preventing the entire X chromosome from separating properly; the result is that the early embryo dies.
Researchers have known that DNA in heterochromatin evolves faster than in other parts of the genome. Also, during early development, the proteins required for cell division come from the mother. The researchers speculate that the heterochromatin of the male D. melanogaster's X chromosome has rapidly evolved, such that after mating, the machinery involved in DNA packaging from a D. simulans mother no longer recognizes the D. melanogaster father's "junk" DNA, Ferree said.
The problematic region of D. melanogaster's X chromosome contains about 5 million base pairs of DNA, while the same region of D. simulans' X chromosome contains only about 100,000 base pairs, a 50-fold difference, said Ferree.
"It points to a species-specific difference in heterochromatin between these two species," he added. "This could explain other instances when you have female hybrid lethality," Ferree said.
Cornell University
Now, Cornell researchers report in the October issue of Public Library of Science Biology (Vol. 7, No. 10) that rapidly evolving "junk" DNA may create incompatibilities between two related species, preventing them from reproducing. In this case, the researchers studied crosses between closely related fruit flies, Drosophila melanogaster and D. simulans. Nearly 100 years ago, scientists discovered that when male D. melanogasters mate with female D. simulans, normal males survive, but the female embryos die.
"It has remained an unsolved problem," said Patrick Ferree, the paper's lead author and a postdoctoral researcher in the lab of co-author Daniel Barbash, an assistant professor of molecular biology and genetics. "The question is, what are the elements that are killing these female hybrids and how are they doing that?"
The researchers found that the female hybrid embryos died very early in development. In most species, when the male's sperm (carrying either an X or Y chromosome) fertilizes the female's egg (containing an X chromosome), a new cell forms with a single nucleus containing a sex chromosome from each parent. If the offspring inherits its father's X chromosome, it becomes female; if it inherits a Y chromosome, it becomes male. Ferree and Barbash found that a unique segment of DNA in the father's X chromosome leads to embryo death of hybrid females.
The segment of DNA was found in the chromosome's heterochromatin, a densely packed region of highly repetitive sequences of junk DNA near the chromosome's center.
During the embryo's initial divisions, the researchers found, a specific segment of heterochromatin gets "sticky" and halts the process, preventing the entire X chromosome from separating properly; the result is that the early embryo dies.
Researchers have known that DNA in heterochromatin evolves faster than in other parts of the genome. Also, during early development, the proteins required for cell division come from the mother. The researchers speculate that the heterochromatin of the male D. melanogaster's X chromosome has rapidly evolved, such that after mating, the machinery involved in DNA packaging from a D. simulans mother no longer recognizes the D. melanogaster father's "junk" DNA, Ferree said.
The problematic region of D. melanogaster's X chromosome contains about 5 million base pairs of DNA, while the same region of D. simulans' X chromosome contains only about 100,000 base pairs, a 50-fold difference, said Ferree.
"It points to a species-specific difference in heterochromatin between these two species," he added. "This could explain other instances when you have female hybrid lethality," Ferree said.
Cornell University
Heterochromatin Current Events and Heterochromatin News RSSA solution to Darwin's 'mystery of the mysteries' emerges from the dark matter of the genome
Biological species are often defined on the basis of reproductive isolation. Ever since Darwin pointed out his difficulty in explaining why crosses between two species often yield sterile or inviable progeny (for instance, mules emerging from a cross between a horse and a donkey), biologists have struggled with this question.
NYU School of Medicine pathology researchers solve another mystery in B lymphocyte development
A new study published online in Nature Immunology ahead of the June 2009 print issue has found that homologous immunoglobulin (lg) alleles pair up in the nucleus at stages that coincide with V(D)J recombination of the heavy and light chain (Igh and Igk) loci.
When every photon counts
The eyes of nocturnal mammals have very large numbers of highly-sensitive rod photoreceptors (the cell type responsible for night vision). They have to perceive light which is less than a millionth of the intensity of daylight.
CSHL researchers explain process by which cells 'hide' potentially dangerous DNA segments
The DNA in the 23 pairs of chromosomes in each of the billions of cells of the human body is so tightly packed that it would measure six feet in length if stretched end to end. A genome of this size can squeeze into a cell's tiny nucleus because it is compressed into highly condensed chromatin fibers by proteins called histones.
Roles of DNA packaging protein revealed by Einstein scientists
Scientists at Albert Einstein College of Medicine of Yeshiva University have found that a class of chromatin proteins is crucial for maintaining the structure and function of chromosomes and the normal development of eukaryotic organisms.
CSHL researchers map changing epigenetic modifications that enable transposons to run amok
Much like cancer cells, plant cells grown for a long time outside of their normal milieu, in culture dishes, have highly unstable genomes.
Stowers Institute's Workman Lab discovers novel histone demethylase protein complex
The Stowers Institute's Workman Lab has discovered a novel histone demethylase protein complex characterized in work published today in Molecular Cell.
Scientists Clarify a Mechanism of Epigenetic Inheritance
Although letters representing the three billion pairs of molecules that form the "rungs" of the helical DNA "ladder" are routinely called the human "genetic code," the DNA they comprise transmits traits across generations in a variety of ways, not all of which depend on the sequence of letters in the code.
Massive project reveals shortcomings of modern genome analysis
The sequencing and comparison of 12 fruit fly genomes -- the result of a massive collaboration of hundreds of scientists from more than 100 institutions in 16 countries -- has thrust forward researchers' understanding of fruit flies, a popular animal model in science.
Where Broken DNA is Repaired
Ionizing radiation, toxic chemicals, and other agents continually damage the body's DNA, threatening life and health: unrepaired DNA can lead to mutations, which in turn can lead to diseases like cancer.
More Heterochromatin Current Events and Heterochromatin News Articles
 |
Heterochromatin: Webster's Timeline History, 1952 - 2007 by Icon Group International (Author) Webster's bibliographic and event-based timelines are comprehensive in scope, covering virtually all topics, geographic locations and people. They do so from a linguistic point of view, and in the case of this book, the focus is on "Heterochromatin," including when used in literature (e.g. all authors that might have Heterochromatin in their name). As such, this book represents the largest compilation of timeline events associated with Heterochromatin when it is used in proper noun form. Webster's timelines cover bibliographic citations, patented inventions, as well as non-conventional and alternative meanings which capture ambiguities in usage. These furthermore cover all parts of speech (possessive, institutional usage, geographic usage) and contexts, including pop culture, the arts,... |
|
CHROMOSOMES OF ANTELOPE SQUIRRELS (GENUS AMMOSPERMOPHILUS): A SYSTEMATIC BANDING ANALYSIS OF FOUR SPECIES WITH UNUSUAL CONSTITUTIVE HETEROCHROMATIN. by J. & J. Mazrimas Mascarello (Author), Plates (Illustrator) | |
 |
Silencing, Heterochromatin and DNA Double Strand Break Repair by Kevin D. Mills (Author) The field of DNA repair is vast and advancing rapidly. Silencing, Heterochromatin and DNA Double Strand Break Repair probes the relationship of DNA break repair and silent heterochromatin, using budding yeast as a model. The primary research presented in this book represents some of the most important work in this new field of inquiry. |
 |
Heterochromatin: Molecular and Structural Aspects by Ram Sagar Verma (Editor) Ram Verma has assembled ten distinguished contributors to survey what is currently known about the relationship of the structure of DNA to its role in the function and expression of genes. The crucial role of heterochromatin in the organization of chromosomes is thoroughly explored in this resulting landmark edited volume. Cytogeneticists and other geneticists, molecular biologists, cytologists, biochemists and their advanced students will also find this an invaluable reference source. |
 |
RNA Interference (Current Topics in Microbiology and Immunology) by Patrick J. Paddison (Author), Patrick J. Paddison (Editor), Peter K. Vogt (Editor) In the last few years the major effect that RNAi has had in invertebrate systems like C.elegans and drosophila is beginning to take hold in mammalian systems through both single gene knockdown experiments and genome-scale screens. In the next decade, there will no doubt be both notable successes and failures as we attempt to apply this genetic tool to various biological problems for the first time in academia and industry. Through the introduction of RNAi, mammalian systems have finally gained admittance to the pantheon of model genetic systems. |
 |
Protein Complexes that Modify Chromatin. Current Topics in Microbiology and Immunology, No. 274 by Jerry L. Workman (Editor) This book provides timely reviews of several protein complexes that regulate gene expression and chromatin dynamics. Examples of such complexes include: nucleosome assembly complexes, ATP-dependent chromatin remodeling complexes, histone acetyltransferase complexes, histone deacetylase complexes, heterochromatin complexes, SMC complexes and transcription elongation complexes. These chapters will bring experts in the field up to date on several aspects of chromosome biology and will provide an exiting introduction to the field for new chromatin researchers. |
|
Can variants in the constitutive heterochromatin of human chromosomes be detected consistently? by Michelle F Browner (Author) | |
|
Polytene chromosomes, heterochromatin, and position effect variegation (Advances in genetics) by I. F Zhimulëv (Author) |
| © 2009 BrightSurf.com |