AR Highlights, February 2013
Correspondence to: Dr. Ellen C. Jensen; 35 Southern Cross Rd., Kohimarama, Auckland 1071, New Zealand. E-mail: email@example.com
Migration of Resident Cardiac Stem Cells in Myocardial Infarction by Simon X. Liang and William D. Phillips. Anat Rec 296:184–191
The discovery of resident cardiac stem cells has changed the view that the heart is a terminally differentiated organ. Loss of cardiomyocytes caused by ischemic necrosis and apoptosis leads to myocardial infarction. Therefore, being able to repair or regenerate myocardium by stem cell therapy is desirable. This can be achieved through resident cardiac stem cells. Their effectiveness depends on their migration from surrounding tissue to the infarct area where they proliferate, differentiate, and subsequently repair the damaged myocardium. The authors discuss several pathways that regulate this migration of different populations of cardiac stem cells. These pathways include the stromal cell-derived factor 1/C-X-C chemokine receptor type 4 pathway, which appears to play an important role in migration of cardiac side population cells, stem cell antigen 1+ cells, and cardiosphere-derived cells. Migration of cytokine receptor c-kit (c-kit+) cardiac stem cells (unable to undergo self-renewal and differentiation into cardiomyocytes) is mediated by hepatocyte growth factor/c-met, stem cell factor/c-kit, and EphrinA1/EphA2 pathways. Hypoxia-inducible transcription factors may be involved in regulating cardiac stem cell migration and proliferation because they are upstream regulators of many genes involved in these processes. Therefore, hypoxic preconditioning treatment may be a good strategy to enhance the efficiency of stem cell therapy for repairing the heart. The authors conclude that understanding of the pathways involved in the migration of resident cardiac stem cells could be important for developing new strategies for treating ischemic myocardium.
Steep Increase in Myonuclear Domain Size During Infancy by Tammo Delhaas, Sander F.T. Van Der Meer, Gert Schaart, Hans Degens, and Maarten R. Drost. Anat Rec 296:192–197
Muscle cells, or myofibers, are multinucleated. This aspect of skeletal muscle has led to the concept of the myonuclear domain. The myonuclear domain is defined as the theoretical amount of cytoplasm in a muscle fiber controlled by a single myonucleus. According to this concept, muscle fiber atrophy is associated with a proportional loss of myonuclei, whereas hypertrophy involves a proportional increase in the number of myonuclei. Little is known regarding development of human myonuclear domain size. The authors examined the time course of the myonuclear domain area and satellite cell density from 1 week after birth until adolescence in humans. They found that satellite cell density declined in early infancy, and this was not accompanied by a corresponding increase in the number of myonuclei per muscle fiber. As a result, myonuclear domain size rapidly increased in the first months following birth, with a reduced rate of increase thereafter, reaching adult values by the young adolescent phase. The authors' data provide some reference values for normal muscle growth. In muscular diseases, loss of muscle mass and function are caused by failure of proliferation and differentiation of satellite cells, which repair ongoing damage to the muscle under the disease state. The authors' reference values may be useful for evaluating therapies for muscle diseases in children.
Forelimb to Hindlimb Shape Covariance in Extant Hominoids and Fossil Hominins by Melissa Tallman. Anat Rec 296:296–304
Examination of the postcranium is usually performed using body proportions. Limb proportions are important for determining locomotor modes in the fossil record because locomotor modes are strongly correlated with positional behavior. However, few skeletons are available in the fossil record that has preservation of both a full forelimb and hindlimb. Therefore, large errors are often associated with estimates of full limb lengths. The author aimed to investigate the postcranium in an integrated manner to avoid having to estimate limb proportions. The author obtained three-dimensional geometric morphometrics that allow for retention of shape information. Two-block partial least squares analyses were performed to investigate covariation between forelimb and hindlimb components in present-day hominoids and fossil hominins. Shape covariation can be used to investigate how multiple bones in the postcranium can function as a unit. The author found a strong correlation between shape covariance in the forelimb and hindlimb. Correlation between these data could be an important proxy for inferring locomotor pattern in incomplete specimens that often are found in the fossil record. Overall, the author's results suggest that fossils have morphological patterns that are most similar to Homo (modern humans), except for when the distal femur was used in the analyses. The author concludes that some fossil hominins may have had locomotor capabilities similar to humans, whereas others had a unique compromise between terrestrial bipedality and other positional behavior not observed in living hominoids.
Ellen C. Jensen*
The Anatomical Record