Proteinuria and perinatal lethality in mice lacking NEPH1, a novel proteinwith homology to NEPHRIN

A high-throughput, retrovirus-mediated mutagenesis method based on gene tra pping in embryonic stem cells was used to identify a novel mouse gene. The human ortholog encodes a transmembrane protein containing five extracellula r immunoglobulin-like domains that is structurally related to human NEPHRIN , a protein associated with congenital nephrotic syndrome. Northern analysi s revealed wide expression in humans and mice, with highest expression in k idney, Based on similarity to NEPHRIN and abundant expression in kidney, th is protein was designated NEPH1 and embryonic stem cells containing the ret roviral insertion in the Neph1 locus were used to generate mutant mice, Ana lysis of kidney RNA from Neph1(-/-) mice showed that the retroviral inserti on disrupted expression of Neph1 transcripts, Neph1(-/-) pups were represen ted at the expected normal Mendelian ratios at 1 to 3 days of age but at on ly 10% of the expected frequency at 10 to 12 days after birth, suggesting a n early postnatal lethality, The Neph1(-/-) animals that survived beyond th e first week of life were sickly and small but without edema, and all died between 3 and 8 weeks of age. Proteinuria ranging from 300 to 2,000 mg/dl w as present in all Neph1(-/-) mice, Electron microscopy demonstrated NEPH1 e xpression in glomerular podocytes and revealed effacement of podocyte foot processes in Neph1(-/-) mice. These findings suggest that NEPH1, like NEPHR IN, may play an important role in maintaining the structure of the filtrati on barrier that prevents proteins from freely entering the glomerular urina ry space.