Early transverse tubule development begins in utero in the sheep heart.
Journal of Muscle Research and Cell Motility
© Springer International Publishing Switzerland 2017
Reason for embargo
The ventricular cardiomyocytes of adult mammals contain invaginations of the plasma membrane known as transverse (t)-tubules. These regular structures are essential for the synchronisation of excitation-contraction (EC) coupling throughout the cell, which is a vital process for cardiac function. T-tubules form a close association with the sarcoplasmic reticulum (SR) to form junctions, where several key proteins involved in EC coupling are localised, including the SR calcium release channels-the ryanodine receptors (RyR). The lipophilic SR protein junctophilin-2 (JPH2) has been implicated in the development of both the junctions and t-tubules. Several studies have identified that t-tubules develop only postnatally in rodents, while historical electron microscopy data indicate that this is not the case in larger mammals, including humans. We have performed, to our knowledge, the first fluorescent, target-specific study to characterise t-tubule development in the large mammalian fetal heart, focussing on the sheep. T-tubules were present in fetal sheep hearts from 114 days gestation (with term being 145 days), with occurrence progressively increasing with gestational age, and further maturation after birth. This was accompanied by an increasing intracellular localisation of JPH2, which progressively increased its association with RyR within the cardiomyocytes as they undergo hypertrophy. These findings indicate that large mammalian hearts exhibit a significantly different temporal pattern of development compared to that of the rodent. Our findings have potential implications for human cardiac development, including the future investigation of congenital heart disease.
This research was supported by a Health Research Council of New Zealand grant (#12/240) awarded to CS. We wish to thank Prof Laura Bennet, Dr Joanne Davidson and the Fetal Physiology & Neuroscience group, Department of Physiology, University of Auckland for supplying the tissue used in this study, with original projects supported by Health Research Council of New Zealand research grants (#14/216 and #12/613).
This is the author accepted manuscript. The final version is available from Springer Verlag via the DOI in this record.
First Online: 06 January 2017
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