March 2013 Archives

Telomeres and Caloric Restriction

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I came across a paper that was published at the beginning of this year that discusses how restricting calorie intake can protect chromosomes. I consider this topic part of developmental biology because I think that aging is still part of development. This type of development is just less positive because it has negative effects.

Telomeres are known to be the judgement of aging. They are located at the ends of chromosomes, and the more humans age, the shorter the telomeres get due to DNA replication. Reduced telomeres can increase the risk of cancer and other age-related illnesses. Vera and colleagues studied adult mice and found that lowering the mice caloric intake over time results in a delay of telomere shortening.

Literature Cited:

Elsa Vera, Bruno Bernardes de Jesus, Miguel Foronda, Juana M. Flores, Maria A. Blasco. Telomerase Reverse Transcriptase Synergizes with Calorie Restriction to Increase Health Span and Extend Mouse Longevity. PLoS ONE, 2013; 8 (1): e53760 DOI: 10.1371/journal.pone.0053760

Melanin

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Melanin is present in human's skin, hair, and eyes. It is also important in protecting the skin from UV radiation. Melanoblasts rise from the neural crest in the developing embryo; in particular, the second month of development. The destination of these melanoblasts include the dermis, epidermis, uveal tract of eye, hair follicles, the stria vasculare, the vestibular organ and endolymphatic sac of the ear, and leptomeninges of the brain. Migration and development in the dermis takes 10-12 weeks and 12-14 weeks for the epidermis. Upon reach of destination, the melanoblasts differentiate into melanocytes, which typically occurs at six months in the developing fetus. Melanocytes in the epidermis continue to replicate and produce melanin; whereas, the dermal melanocytes decrease in number during gestation, and eventually disappear at birth.

Melanin synthesis occurs in membrane bound organelles called the melanosomes, which are produced by the melanocytes. The differences in skin color between people is based on cutaneous pigmentation. After production of melanin by melanocytes, the melanosomes must be transferred to surrounding keratinocytes. The abundance of melanocytes relatively constant in all skin types; however, the size and distribution differs within keratinocytes. The difference between dark and light skin color is that darker skinned people have many large and dense melanosomal particles; whereas, light skin color has smaller particles and are less dense. The melanosome type and distribution is present at birth.

The mechanism for how melanin helps to protect the skin from UV radiation is melanin accumulates above the nucleus and absorbs the UV-rays before they reach the nucleus and damage the DNA.

Literature Cited:

Costin, G.E., Hearing, V.J. 2007. Human skin pigmentation: melanocytes modulate skin color in response to stress. The FASEB Journal. 21(4): 976-994.

An article was published a few days ago (March 21) that is going to cause textbooks to be re-written because of what they found. Thompson and Tucker used transgenic mice to track the developmental process of the middle ear. The mechanism that they found gives a reason why the ear is prone to infection. Two types of tissues are used when developing the middle ear, which are the neural crest and the endoderm. The difference between these two types of tissues is that the endoderm gives rise to the tissue lining that is covered with cilia; whereas, the neural crest gives rise to he tissue lining with absence of the cilia. The purpose of cilia is to remove debris from the ear. Therefore, the tissue that originate from the neural tube are not efficient at removing debris due to the lack of cilia.

The middle ear is a air filled space, something that is unique to mammals. Reptiles and birds do not have this air filled space, probably because they only have one ear bone, while mammals have three. It is suggested that the evolved air filled spaced was needed to proved room for the additional two bones. Thus, the two types of tissue lining in the middle ear might have evolved due to the air filled space. Even though the evolution of these two types of tissues was to make space for the additional two bones needed for hearing in the mammals ear, it allowed the chances of infection to increase. The lining with no cilia cannot efficiently remove debris from the ear, leading it to be more prone to infection. This was discussed in the review as an "evolutionary glitch".

Literature Cited:

Hannah Thompson and Abigail S. Tucker. Dual Origin of the Epithelium of the Mammalian Middle Ear. Science, 2013; 339 (6126): 1453-1456 DOI: 10.1126/science.1232862

http://www.sciencedaily.com/releases/2013/03/130321141453.htm

Review of Mile's Blog on Gynandromorphy

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For our class blog assignment this week, professor Myers wanted us to read a blog from another student, comment, and then write our own blow review it.

Miles' blog on gynandromorphy!

Going over the different entries, the half red half white bird caught my eye. This blog written by Miles is on gynandromorphy. Gynandromorphy is a condition where an organism has both male and female parts. The picture in this blog is of a cardinal. This occurs when the sex chromosomes do not separate equally in mitosis, and this causes a cell to contain both male and female sex chromosomes. An example is for a male (XY) to produce a cell with X and the other with XYY. The XYY cell then can develop into an organism that has bilateral symmetry of male and female structures.

I asked on his blog which color represents which sex. With some of my own research. It turns out that the male would be red reflecting the idea of sexual selection where the brighter color would attract females. The female would be a mix of a dull grey/white/red. I also asked if the organism is hermaphroditic. It turns out that hermaphrodites have reproductive organs or male and female, but the exterior characteristics are normal. An example is that there may be a butterfly that is a female, but has a male wing.

This condition is unique to cardinals because it does not occur in other birds. However, it does happen to other organisms like the butterfly shown below:
Tiger swallowtail.jpg
Tiger swallowtail: Males are yellow with black stripes, while females appear a dark blue.

Picture was from: http://e11e-k.deviantart.com/art/Gynandromorph-208458484

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