CIC-2: a developmentally dependent chloride channel expressed in the fetal lung and downregulated after birth.

Abstract

Growth and differentiation of the fetal lung are dependent on chloride and fluid secretion, yet the specific molecular identities of fetal chloride channels have not been fully determined. In this study, we demonstrate mRNA expression of the volume-activated chloride channel, CIC-2, in fetal rat lung using reverse-transcriptase polymerase chain reaction (RT-PCR) and ribonuclease (RNase) protection assay. By RNase protection assay, CIC-2 mRNA expression is most abundant in fetal lung and diminishes after birth until it is almost undetectable in adult rat lung. To confirm this result at the protein level, a C-terminal fragment of CIC-2 cDNA derived from 19-day fetal rat lung was cloned into an expression plasmid. The truncated 33-kD CIC-2 protein was expressed in Escherichia coli and purified by column chromatography. Polyclonal antibodies to this antigen were raised in chickens, and the antisera detected a 94-kD protein in fetal rat lung homogenates by Western blotting. Protein expression of CIC-2 was most abundant in mid and late gestation and decreased significantly shortly after birth, as would be predicted by the RNase protection data. CIC-2 protein was localized along the apical surface of fetal airway epithelium by immunocytochemistry. The abundant fetal expression of CIC-2 RNA and protein supports the hypothesis that CIC-2 is important to fetal lung development, and its apical location suggests that it may be involved in fluid secretion during normal lung morphogenesis.

Ionotropic GABA receptor expression in the lung during development

“…Similar to CFTR and ClC in the developing lungs (Brochiero et al, 2004;Blaisdell et al, 2000;Harris et al, 1991;Murray et al, 1996;Lamb et al, 2001;Murray et al, 1995), the mRNA of some GABA receptor subunits (Group 1, Fig. 2A) were relatively high in mid-gestation, but decreased in late gestation and remained low in adult.…”

“…Some of the channels have been shown to be involved in fluid homeostasis in fetal and adult lungs (Brochiero et al, 2004;Blaisdell et al, 2000;Fang et al, 2002). These Cl − channels appear in early gestation and are expressed relatively high throughout the fetal stage, but decrease at late gestation and remain low during adult stages (Harris et al, 1991;Murray et al, 1996;Lamb et al, 2001;Murray et al, 1995). The Cl − channels may participate in fluid secretion in fetal lungs since the lung undergoes a change from fluid secretion to absorption at birth.…”

3q26.33–3q27.2 microdeletion: A new microdeletion syndrome?

“…CLCN2, a gene for which the mice knock-out model of its homolog demonstrates leukoencephalopathy [10] and degeneration of retinal and testicular cells, leading to male infertility is present in the deleted region [11]. The CLCN2 rat homolog is expressed in fetal lung and its expression rapidly decreases after birth; therefore its deficiency may be related to the neonatal respiratory distress [12] and testicular anomalies observed in our patients.…”

Additional Disruption of the ClC-2 Cl- Channel Does Not Exacerbate the Cystic Fibrosis Phenotype of Cystic Fibrosis Transmembrane Conductance Regulator Mouse Models

“…Furthermore, several studies suggested that ClC-2 may be present in apical membranes of lung (18) and intestinal (19,33) epithelia, although others obtained conflicting results (34,35). Finally, the testicular and retinal degeneration observed in Clcn2 Ϫ/Ϫ mice was suggested to result from a defect in transepithelial transport across the Sertoli cell and retinal pigment epithelium, respectively (24).…”

“…Immunocytochemical studies have suggested that ClC-2 is expressed in the apical membranes of lung and intestinal epithelia (18,19), where it may transport Cl Ϫ in a pathway that is independent of and parallel to CFTR. Thus, ClC-2 appears to be a prime candidate for an alternative pathway for Cl Ϫ secretion in CF (20 -22).…”