Category: Physiology

Molecular Basis of Temperature-Dependent Gender of Red-Eared Slider Turtle

Imagine a child inside a womb with a sex yet to be decided not by the pair of sex chromosomes but by the ambient temperature – well, that is how the sex of red-eared slider turtle (Trachemys scripta elegans) and other reptile species is determined. Whether the baby red-eared slider turtle develops into a male or female will depend on the ambient temperature of the nest. The eggs hatching from a cooler nest will be males whereas those in a warmer nest will be females. Nevertheless, scientists recently identified the molecular basis associated with the temperature-dependent sex determination in red-eared slider turtle.
 
 
 

Temperature-dependent sex determination in red-eared slider turtle

Red-eared slider turtle.

Photo by Greg Hume, WikiMedia Commons under CC BY-SA 3.0 license.


In humans, the sex of the offspring is determined by the pair of chromosomes inherited from the parents. At fertilization, the sex of the embryo is already determined. A female embryo would have two X chromosomes whereas a male embryo would have X and Y chromosomes. This mechanism of sex-determination is referred to as genotypic sex determination (GSD). This is also how the sex of many animals, including certain reptiles, is determined. Another mechanism is temperature-dependent sex-determination (TSD). It is when the temperature predicts the sex of the developing embryo. This is observed in many reptiles, such as crocodiles, alligators, and turtles. In red-eared slider turtle, for instance, their sex can be predicted depending on the incubation temperature. There is a critical period during which the embryonic development is thermosensitive. Red-eared slider turtle eggs hatching from cooler nests will all be males whereas those hatching from warmer nests will all be females.1
 
 
 

Molecular basis of sex-determination in red-eared slider turtle

Red-eared slider turtle laying egg.

Photo by Nephets, WikiMedia Commons under CC BY-SA 3.0 license.


How the temperature causes the baby red-eared slider turtle to turn into male or female is a long-time enigma. The phenomenon of TSD was observed for more than 50 years ago and since then scientists have attempted to dig further into the molecular level of TSD. Are there genes involved in the process, and if there are, which genes? Researchers from Duke University and Zhejiang Wanli University in China published their study on red-eared slider turtle.2 Eggs incubated at 32 °C hatched as females while those incubated at coolertemperature (26 °C) hatched as males. When they silenced the Kdm6b gene the eggs that suppossedly would develop into males at cooler temperature (26 °C) hatched as females. Knockdown of Kdm6b red-eared slider turtle babies developed ovaries rather than testes.
 
 
 

The molecular role of red-eared slider turtle Kdm6b gene

Kdm6b gene appears to be the key gene essential to turning on the switch of “maleness” in red-eared slider turtle. The activity of this gene is vital during the critical period of gonad development. It became more active at cooler incubation temperature and then “silent” at warmer temperature. 1 The gene promotes directly the transcription of the male sex-determining gene, Dmrt1. It does so by coding for a protein that removes the trimethylation of the histone, H3K27, near the promoter region of Dmrt1. 2 The methyl tags of the histone repress DNA activity and therefore removing them would allow expression of the genes along the DNA molecule.
 
 
 
This study was unable to identify the temperature-sensing trigger since the Kdm6b and its protein were not inherently sensing temperature changes. 1 For now, the molecular basis of the temperature-dependent sex-determination in the red-eared slider turtle as described above has not reached completion. Nonetheless, what was currently discovered in the red-eared slider turtle may serve as a model to understand the underlying mechanism in other reptile species where temperature is a major sex-determining factor.
 
 
 
— written by Maria Victoria Gonzaga
 
 
 
References:
1 Duke University. (2018). How turning down the heat makes a baby turtle male: Scientists start to crack 50-year puzzle of how temperature influences a hatchling’s sex. ScienceDaily. Retrieved from www.sciencedaily.com/releases/2018/05/180510203722.htm
2 Ge, C., Ye, J., Weber, C., Sun, W., Zhang, H., Zhou, Y., Cai, C., Qian, G., & Capel, B. (2018). The histone demethylase KDM6B regulates temperature-dependent sex determination in a turtle species. Science 360 (6389): 645.

Maternal and neonatal outcomes of respiratory failure during pregnancy

Respiratory failure is an outcome from inadequate gas exchange wherein arterial oxygen and carbon dioxide not at normal levels. A drop of oxygen is called hypoxemia while the rise in arterial carbon dioxide is hypercapnia. Respiratory failure includes abnormal blood gases, increased of breathing and increased respiratory rate. In obstetric patients a complicated conditions occurs resulting to various complications and several physiological changes.  That is why risk of complication in pregnancy with respiratory failure considered challenge for positive maternal and neonatal outcomes.

 

Causes in Maternal Respiratory failure

The main causes of respiratory failure were postpartum hemorrhage, peripartum period, preeclampsia and pneumonia during pregnancy. In which the oxygen reserve impairment during pregnancy causes fast desaturation leading to fetal hypoxia. Many of the patients showed improvement after delivery in partial pressure of arterial oxygen. But some exhibited high incidence of neonatal respiratory distress syndrome. Neonatal complications were commonly caused by sepsis and meconium aspiration syndrome as well as impairment in neurological development.

 

Acute respiratory distress syndrome is classified as mild to severe injuries from aspiration, trauma and multiple transfusions. It is also a condition of newborn having dyspnea with cyanosis that is often related to surfactant deficiency. However, preterm infant retinas showed incomplete retinal vascularization. On the other hand obstetric patients showed 74% having maternal respiratory failure complications while 25.4% to non-obstetric patients.

 

Indeed, early delivery might improve maternal oxygenation and reduce mortality rate. However maternal respiratory failure may not always improve after the delivery wherein deleterious sepsis and lung injury persist after delivery. Additionally a detailed examination is needed to follow up the neonates in the future. Using the risk categories whether normal, questionable and abnormal, if the mental developmental index is <70 then the neonates are suspected to have mental retardation.

 

Source: Prepared by Joan Tura from    Journal of the Formosan Medical  Association

Volume 117, Issue 5, May 2018, Pages 413-420

Epstein-Barr Virus – It’s More Than Just The Kiss

Epstein-Barr virus — the virus causing the kissing disease or mononucleosis — is eyed as a risk factor for contracting seven other major diseases. This is what the research team at Cincinnati Children’s Hospital Medical Center reported. Epstein-Barr virus is contracted by kissing or by the oral transfer of saliva. Apparently, once the Epstein-Barr virus infects the body it stays there forever.
 
 
 

Epstein-Barr virus and mononucleosis

Epstein-Barr virus illustration.
(Credit: Vix Maria, ©Biology-Online.org)

Epstein-Barr virus belongs to the herpes family, Herpesviridae. It contains DNA that bears 85 genes and is surrounded by a nucleocapsid. Apart from the nucleocapsid, the virus is further bounded by a protein tegument and an outermost layer of a lipid envelope. The envelope has glycoprotein projections, which are crucial for the virus during its infection of the host cell.1 B cells, the immune cells producing antibodies, are ought to destroy them. However, the Epstein-Barr virus can outwin them by a slick mechanism. The virus invades the B cell, reprograms it, and makes it “follow” its “commands”. The virus is known for causing mononucleosis or the kissing disease. The common symptoms include fever, fatigue, sore throat, rash, and swollen lymph nodes, especially in the neck.
 
 
 

Epstein-Barr virus and the seven major diseases

According to the study led by three scientists, John Harley, Leah Kottyan, and Matthew Weirauch, the Epstein-Barr virus infection has been implicated to seven unrelated serious diseases.2 Previous studies by Dr. Harley and his team have already connected Epstein-Barr virus with the increased risk of developing systemic lupus erythematosus years ago. Recently, however, they found that the virus could also augment the risk of developing other serious diseases, such as multiple sclerosis, type 1 diabetes, inflammatory bowel disease, celiac disease, rheumatoid arthritis, and juvenile idiopathic arthritis.3 A person contracting the Epstein-Barr virus has a greater risk of developing them. This is because the virus produces a protein, Epstein–Barr virus nuclear antigen 2 (EBNA-2), that interacts with the human DNA, especially at genetic risk variants. 2 A genetic risk variant pertains to a variant in the DNA genome that has a potential to cause disease(s).
 
 
 

Epstein-Barr virus and future research

Epstein-Barr virus, known for causing kissing disease or mononucleosis, is linked to other serious diseases.

Dr. Harley and his team suspect that the EBNA2 protein from the Epstein-Barr affects a set of transcription factors. Accordingly, what the seven seemingly unrelated diseases share in common is a set of dysfunctional transcription factors, each affected by the EBNA2 protein.2 When the activity of transcription factors deviate from what they are supposed to do, the host cell (such as B cell) would not be able to carry out its normal function. This, in turn, could progress to certain diseases. With their recent finding, Dr. Harley and his team is optimistic that further intensive research could direct to finding better therapies and preventive methods such as vaccines against Epstein-Barr virus infection.
 
 
 
This recent finding suggests that contracting Epstein-Barr virus can lead to multiple diseases apart from mononucleosis. Therefore, this calls for more studies that aim at finding better cures and preventive measures. Currently, there is no vaccine against Epstein-Barr virus; being able to boost our immunity against the virus may help mitigate the risk to many other diseases, such as those mentioned above.
 
 
 
— written by Maria Victoria Gonzaga
 
 
 
References:
1Odumade, O.A., Hogquist, K.A., & Balfour Jr., H.H. (2011). “Progress and Problems in Understanding and Managing Primary Epstein–Barr Virus Infections”. American Society for Microbiology. 24 (1): 193–209. doi:10.1128/CMR.00044-10
2 Harley, J.B., Chen, X., Pujato, M., Miller, D., Maddox, A., Forney, C., Magnusen, A.F., Lynch, A., Chetal, K., Yukawa, M., Barski, A., Salomonis, N., Kaufman, K.M., Kottyan, L.C., & Weirauch, M.T. (2018). “Transcription factors operate across disease loci, with EBNA2 implicated in autoimmunity.” Nature Genetics. DOI: 10.1038/s41588-018-0102-3
3 Cincinnati Children’s Hospital Medical Center. (2018). ‘Mono’ Virus Linked to Seven Serious Diseases. Retrieved from https://www.cincinnatichildrens.org/news/release/2018/mono-virus.

How Celiac Disease Affects The Digestive System

Celiac disease is a condition that affects the digestive systems of many individuals all over the world, and in this article, the goal is to explain it in a way that anyone can understand what’s really happening. We might even include some intense action (like in the movies).

The digestive system is a beautiful thing. We start breaking down that tasty food in our mouths by chewing it, and enzymes in our saliva even starts to break down the carbohydrates that are present in our food. It then takes the journey down your pharynx to your esophagus and ends up in the stomach. (more…)