Characterization of connexin31.1-deficient mice reveals impaired placental development.

The gap junction gene Connexin31.1 has been reported to be expressed predominantly in the epidermis of murine skin. To study the function of this gene, we generated mice in which the coding DNA of the Connexin31.1 gene was replaced by lacZ reporter coding DNA. Using beta-galactosidase staining, we have shown that lacZ/Connexin31.1 was expressed in the spinous and granular layers of the epidermis, in cells of olfactory epithelium and in the vomeronasal organ. During embryogenesis, Connexin31.1 was co-expressed with another isoform, Connexin31, in the post-implantation trophoblast cell lineage and, later in gestation, in placental glycogen cells. Although homozygous Connexin31.1-deficient mice were fertile and showed no morphological or functional defects in adult organs expressing this gene, 30% of the offspring expected according to Mendelian inheritance were lost between embryonic days 11.5 and 14.5 and surviving embryos were significantly reduced in weight near the end of pregnancy. Placentas of Connexin31.1-deficient embryos were reduced in weight and showed altered morphology of the spongiotrophoblast and labyrinth layer. The spongiotrophoblast formed a compact barrier at the decidual border that might restrict the maternal blood supply. We conclude that Connexin31.1 is critical for normal placental development but appears to be functionally compensated by other connexin isoforms in the embryo proper and adult mouse.

Characterization of connexin30.3-deficient mice suggests a possible role of connexin30.3 in olfaction.

We have generated connexin30.3-deficient mice in which the coding region of the connexin30.3 gene was replaced by the lacZ reporter gene. The expression pattern of this connexin was characterized using beta-galactosidase staining and immunoblot analyses. In skin, beta-galactosidase/connexin30.3 protein was expressed in the spinous and granulous layers of the epidermis. Specific beta-galactosidase/connexin30.3 expression was also detected in the thin ascending limb of Henle's loop in the kidney. In addition, we found beta-galactosidase/connexin30.3 in progenitor cells of the olfactory epithelium and in a subpopulation of cells in the apical layer of the vomeronasal organ. Connexin30.3-deficient mice were fertile and displayed no abnormalities in the skin or in the chemosensory systems. Furthermore, they showed normal auditory thresholds as measured by brain stem evoked potentials. These mice did, however, exhibit reduced behavioural responses to a vanilla scent.

Connexin 30.3 is expressed in the kidney but not regulated by dietary salt or high blood pressure.

Several isoforms of connexin (Cx) proteins have been identified in a variety of tissues where they play a role in intercellular communication, either as the components of gap junctions or as large, nonselective pores known as hemichannels. This investigation seeks to identify the localization and regulation of Cx30.3 in mouse, rat, and rabbit kidney using a Cx30.3(+/lacZ) transgenic approach and immunofluorescence. Cx30.3 was detected in all three species and predominantly in the renal medulla. Both the nuclear lacZ staining indicative of Cx30.3 expression and indirect immunohistochemistry provided the same results. Cx30.3 immunolabeling was mainly punctate in the mouse, typical for gap junctions. In contrast, it showed continuous apical plasma membrane localization in certain tubule segments in the rat and rabbit kidney, suggesting that it may also function as hemichannels. In the cortex, Cx30.3 was localized in the intercalated cells of the cortical collecting duct, because the immunoreactive cells did not label for AQP2, a marker for principal cells. In the medulla, dense Cx30.3 staining was confined to the ascending thin limbs of the loop of Henle, because the immunoreactive cells did not label for AQP1, a marker of the descending thin limbs. Immunoblotting studies indicated that Cx30.3 expression was unchanged in response to either high or low salt intake or in spontaneously hypertensive rats. Cx30.3 appears to be constitutively expressed in certain renal tubular segments and cells and its role in overall kidney function remains to be investigated.

The connexin31 F137L mutant mouse as a model for the human skin disease erythrokeratodermia variabilis (EKV).

Erythrokeratodermia variabilis (EKV) is a rare autosomal dominant human genodermatosis. Its clinical appearance varies from transient, fast moving erythemas to persistent brown hyperkeratoses. So far, several mutations in the Cx31 or Cx30.3 gene have been reported to cause EKV in humans. We have generated a conditional mouse mutant that carries the human F137L mutation in the Cx31 gene which was described to act in a transdominant negative manner. The phenylalanine residue at position 137 is highly conserved in several human and mouse connexin genes. Mouse embryonic stem (ES) cells expressing one allele of the Cx31F137L mutation were stable but showed approximately 30% decreased transfer of neurobiotin. This is probably due to dominant negative effects of the Cx31F137L protein on wild type Cx31 and Cx43 protein expressed in ES cells. Surprisingly, the healing process of tail incision wounds in Cx31(+/F137L) mice was shortened by 1 day, i.e. very similar as previously reported for mice with decreased expression of Cx43 in the epidermis. This suggests again that Cx31 and Cx43 proteins functionally interact, possibly by forming heteromeric channels in the epidermis. Heterozygous Cx31(+/F137L) mice are viable and fertile, in contrast to homozygous Cx31(F137L/F137L) mice that die around ED 7.5. In Cx31(+/F137L) mice, the epidermal expression pattern and level of Cx26, Cx30, Cx30.3 and Cx43 proteins were not altered compared with wild-type mice. No erythemas were detected in young C31(+/F137L) mice before 2 weeks of age. In contrast to human EKV patients, hyperproliferation of the stratum germinativum was found in only 5% of the analyzed skin area.