Cool look at the life cycle of a mysterious sea drifter. Imagine the untold millions that never make it to the final stage. Poor little polyps. But them’s the facts of evolution. Some organisms have to send out armies of their young in order to have enough adults survive to carry on the population.
Want some even cooler jelly science? Check out the Turriptopsis jelly, the so-called “immortal jellyfish”. It can go all the way to the adult stage up there, then revert some of its cells back into polyps, sending them off to grow into an entirely new jellyfish! It’s not immortal in the true sense, since no one has proof of multiple generations actually surviving (see “the untold millions” note above), but that’s amazing!!
Anatomy Lesson - The Ribs
Humans have 24 ribs (12 pairs). The first seven sets of ribs, known as “true ribs”, are directly attached to the sternum through the costal cartilage. Rib 1 is unique and harder to distinguish than other ribs. It is a short, flat, C-shaped bone. The vertebral attachment can be found just below the neck and the majority of this bone can be found above the level of the clavicle. Ribs 2 through 7 have a more traditional appearance. The following five sets are known as “false ribs”, three of these sharing a common cartilaginous connection to the sternum, while the last two (eleventh and twelfth ribs) are termed floating ribs (costae fluitantes) or vertebral ribs. They are attached to the vertebrae only, and not to the sternum or cartilage coming off of the sternum. Some people are missing one of the two pairs of floating ribs, while others have a third pair. Rib removal is the surgical excision of ribs for therapeutic or cosmetic reasons.
In general, human ribs increase in length from ribs 1 through 7 and decrease in length again through rib 12. Along with this change in size, the ribs become progressively oblique (slanted) from ribs 1 through 9, then less slanted through rib 12.
Scanning electron micrographs of an embryo at Carnegie stage 10 (approximately week 4)
Purkinje neurons play an essential role in motor function. Here the Purkinje neurons reach their arbor-like dendrites into the molecular layer of the developing cerebellum of a mouse. The mostly green cells at the bottom left are cerebellar granule cells, which relay information from the nervous system to the Purkinje neurons.
Scars are formed by the collagen produced by fibroblasts in the area of the injury. Initially scars may have a raised or bumpy appearance, but over time tend to diminish in size and flatten. Sometimes, however, fibroblasts do not cease to produce collagen at the proper time, and the resultant scar swells with the fibrous protein to unusual proportions. If this growth remains restricted to the original location of the wound then it is referred to as a hypertrophic scar, but if it extends past the boundaries of the injured area, then the overgrown scar is called a keloid.
White Blood Cell chasing and consuming a Bacterial Organism through a process called Phagocytosis
A scanning electron micrograph of a human blastocyst (5 days after fertilization of the egg), revealing the inner cell mass that will become the embryo. Image courtesy of Yorgos Nikas, Wellcome Images
Life. Bits. Self.
The development of human life is an indisputable marvel of choreographed complexity: A single fertilized egg divides and multiplies, the resulting cells differentiating into the roughly 300 cell types required to build a human being.
Among the great and enduring questions of developmental biology is how exactly embryogenesis occurs. What process or plan directs differentiating cells to do what they do, to choose their pathways to becoming neurons, fat cells, hair cells or various hormone secreting cells?
In a paper published today in Cell, a multi-institutional team of scientists, including Bing Ren, PhD, head of the Laboratory of Gene Regulation at the Ludwig Institute for Cancer Research at UC San Diego and professor in the UCSD School of Medicine’s Department of Cellular and Cellular Medicine, describe how genes are turned on and off to direct early human development – and report novel genetic mechanisms that play key roles not just in normal development but perhaps in diseases like cancer as well.
Using large-scale genomics technologies, the researchers focused on two key processes in unprecedented detail. The first involves the tacking of methyl molecules to cytosine, one of the four DNA bases that comprise the genetic code; the second involves chemical modifications to proteins called histones, which provide the scaffolding used by winding DNA in cell nuclei.
Histone modification, the researchers found, is more commonly used to regulate genes in early embryonic development, switching them on and off as needed. “DNA methylation” tends to be used in the later stages of development when cells are increasingly locked into specific fates and functions.
“You can sort of glean the logic of animal development in this difference,” said Ren in a news release issued by the Ludwig Institute. “Histone methylation is relatively easy to reverse. But reversing DNA methylation is a complex process, one that requires more resources and is much more likely to result in potentially deleterious mutations.
“So it makes sense that histone methylation is largely used to silence master genes that may be needed at multiple points during development, while DNA methylation is mostly used to switch off genes at later stages, when cells have already been tailored to specific functions, and those genes are less likely to be needed again.”
The scientists also noted two other significant findings:
- The human genome is pocked with more than 1,200 regions kept consistently free of DNA methylation throughout development. Many master regulator genes reside in these regions, dubbed “DNA methylation valleys.” Interestingly, these regions were found to be abnormally methylated in colon cancer tissues.
- The identification of more than 103,000 “enhancers” or sequences of DNA that can boost the expression and suppression of genes.
Ren said the work creates a new information resource for biomedical research, not just for better understanding of early human development, but also of the many diseases that trace their roots to our own.