Anion exchanger 2 is essential for spermiogenesis in mice

Abstract

Na ؉ -independent anion exchangers (AE) mediate electroneutral exchange of Cl ؊ for HCO 3 ؊ ions across cell membranes, being involved in intracellular pH and cell volume regulation and in transepithelial hydroionic fluxes. Bicarbonate activation of adenylyl cyclase is known to be necessary for sperm motility and sperm capacitation, and a few studies have suggested a possible role of AE carriers in reproduction. Among the four AE genes identified in mammals thus far, only Ae2 (Slc4a2) has been determined to be expressed in the male reproductive system, especially in developing spermatozoa and in epididymal epithelium. Most AE genes drive alternative transcription, which in mouse Ae2 results in several Ae2 isoforms. Here, we generated mice carrying a targeted disruption of Ae2 that prevents the expression of the three AE2 isoforms (Ae2a, Ae2b1, and Ae2b2) normally found in mouse testes. Male Ae2 ؊/؊ mice (but not female Ae2 ؊/؊ mice) are infertile. Histopathological analysis of Ae2 ؊/؊ testes shows an interruption of spermiogenesis, with only a few late spermatids and a complete absence of spermatozoa in the seminiferous tubules. The number of apoptotic bodies is increased in the seminiferous tubules and in the epididymis, which also shows squamous metaplasia of the epididymal epithelium. Our findings reveal an essential role of Ae2 in mouse spermiogenesis and stress the recently postulated involvement of bicarbonate in germ-cell differentiation through the bicarbonate-sensitive soluble-adenylyl-cyclase pathway.

Inefficient Chronic Activation of Parietal Cells in Ae2−/− Mice

“…16 In our Ae2 a,b Ϫ/Ϫ mice there is some antenatal and perinatal death. 27 However, the surviving animals do not display the severe symptoms described in the complete knockout 16 and have a normal life span, although our Ae2 a,b Ϫ/Ϫ show deafness and defective bone development (unpublished observations) similarly to what was reported for Ae2 Ϫ/Ϫ mice. 16 It is unlikely that the observed difference in severity of phenotype is caused by the expression of the Ae2c isoforms because expression of Ae2c1 is limited to the stomach, and in addition to its extremely low widespread expression, Ae2c2 appears to be inactive.…”

“…Previously, we reported the generation of mice with a targeted disruption of the more widely distributed variants Ae2a, Ae2b1, and Ae2b2 but not Ae2c1 and Ae2c2 isoforms, 27 hereby referred to as Ae2 a,b Ϫ/Ϫ mice. This animal model enables us to assess the relative importance of the c isoforms of Ae2.…”

“…27 Animals were bred in heterozygous couples against FVB/N background. All procedures with animals were approved by the Institutional Animal Care and Use Committee.…”

“…17 Because our targeting construct disrupted only Ae2a, Ae2b1, and Ae2b2 messages, 27 one could expect a possible compensatory increase in the expression of Ae2c transcripts, and more in particular of Ae2c1, which in mouse and rat has been reported to be stomach-specific. 14,17,20,22,26,33 However, quantitation by real-time PCR revealed no increase in the gastric expression level of type c transcripts in the Ae2 a,b Ϫ/Ϫ mice.…”

Cl− Channels and Transporters in Sperm Physiology

“…This gene has fi ve splice isoforms (AE2a, AE2b1, AE2b2, AE2c1, AE2c2), and mice lacking their expression die before weaning of severely retarded development (Gawenis et al 2004 ). Mice expressing only the AE2c isoform survive but they are infertile and exhibit testicular dysplasia, consistent with the observation that AE2 is highly expressed in the testis (Medina et al 2003 ).…”