Patterns of Expression of Sarcoplasmic Reticulum Ca ²⁺ -ATPase and Phospholamban mRNAs During Rat Heart Development

Abstract

This study reports the clonal analysis and sequence of rat phospholamban (PLB) cDNA clones and the temporal appearance and patterns of distribution of the mRNAs encoding sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPase (SERCA2) and PLB in the developing rat heart determined by in situ hybridization. Both proteins play a critical role in the contraction-relaxation cycle of the heart. SERCA2 mRNA is already abundantly present in the first stage studied, in the cardiogenic plate of the 9-day-old presomite embryo, before the occurrence of the first contractions. This very early expression makes it an excellent marker for the study of early heart development. Subsequently, SERCA2 mRNA becomes expressed in a craniocaudal gradient, being highest at the venous pole and decreasing in concentration toward the arterial pole of the heart. PLB mRNA can be detected in hearts from 12 days of development onward in a virtually opposite gradient. In essence, these patterns do not change during further development. PLB mRNA levels remain highest in the ventricle and outflow tract, whereas SERCA2 mRNA prevails in the inflow tract and atrium, although the difference between atrium and ventricle becomes less pronounced. These observations are compatible with a model in which the upstream part of the heart (inflow tract and atrium) would have a greater capacity to clear calcium and hence would have a longer duration of the diastole than the downstream compartments (atrioventricular canal, ventricle, and outflow tract), similar to the observed pattern of contraction of the embryonic heart. The sinoatrial and atrioventricular nodes do not reveal an expression pattern of SERCA2 and PLB mRNA that allows one to distinguish them from the surrounding atrial working myocardium. However, the ventricular part of the conduction system, comprising atrioventricular bundle and bundle branches, are almost devoid of SERCA2 mRNA.

Atrial Chamber-specific Expression of Sarcolipin Is Regulated during Development and Hypertrophic Remodeling

“…These changes are similar to those of PLN in the ventricles (21) (22). No ventricular SLN expression was detected at any stage of development or cardiac hypertrophy.…”

Expression pattern and ontogenesis of thyroid hormone receptor isoforms in the mouse heart

“…TR 1 was also ubiquitously expressed at E 9·5, but later in development, namely, E 11·5, E 13·5 and E 15·5, it was progressively confined to the atria, SAN and ventricular trabecular structures that will become the peripheral ventricular conduction system. Our findings could be of great importance for understanding the specific actions of the TR isoforms, because the TR-dependent genes are heterogeneously expressed in distinct cardiac components, and they could be regulated specifically by TR 1, TR 1 or both isoforms (Moorman et al 1995, Franco & Icardo 2001. Moreover, the pleiotropic effect of the mutation in TR 1 is consistent with the wide distribution of TR 1, whereas the more limited alterations generated by the ablation of the TR 1 gene agree with the more restricted pattern of expression observed for TR 1 (Gloss et al 2001).…”

“…Again, in order to identify the distinct cardiac components, we performed in situ hybridization staining for Cx40 and SERCA2a (Moorman et al 1995(Moorman et al , 1998 ). The SAN is identified by the absence of connexin 43 staining (a).…”

“…The regional expression of the TRs can also explain why phospholamban and SERCA2a are predominantly TR 1, but not TR 1, regulated in vivo (Gloss et al 2001, Klein & Ojamaa 2001, Dillmann 2002. Both proteins are highly expressed in the compact myocardium but significantly lower or absent in the trabeculae (Moorman et al 1995). Therefore, the fact that TR 1 is present only in these trabecular structures goes a long way to explain the lack of TR 1 regulation of phospholamban and SERCA2 in vivo.…”

“…Therefore, both Cx40 and Cx43 can be used as negative markers of the SAN, whereas Cx40 can be used as a positive marker for the AVB and PVCS. Since SERCA2a is less expressed in the PVCS of embryonic and fetal heart than in the working, compact myocardium, it has also been used to distinguish these two components of the heart (Moorman et al 1995(Moorman et al , 1998). …”