Oligo-Astheno-Teratozoospermia in Mice Lacking RA175/TSLC1/SynCAM/IGSF4A, a Cell Adhesion Molecule in the Immunoglobulin Superfamily

Abstract

RA175/TSLC1/SynCAM/IGSF4A (RA175), a member of the immunoglobulin superfamily with Ca²⁺-independent homophilic trans-cell adhesion activity, participates in synaptic and epithelial cell junctions. To clarify the biological function of RA175, we disrupted the mouse Igsf4a (Ra175/Tslc1/SynCam/Igsf4a Ra175) gene. Male mice lacking both alleles of Ra175 (Ra175^{− / −}) were infertile and showed oligo-astheno-teratozoospermia; almost no mature motile spermatozoa were found in the epididymis. Heterozygous males and females and homozygous null females were fertile and had no overt developmental defects. RA175 was mainly expressed on the cell junction of spermatocytes, elongating and elongated spermatids (steps 9 to 15) in wild-type testes; the RA175 expression was restricted to the distal site (tail side) but not to the proximal site (head side) in elongated spermatids. In Ra175 ^{− / −} testes, elongated and mature spermatids (steps 13 to 16) were almost undetectable; round spermatids were morphologically normal, but elongating spermatids (steps 9 to 12) failed to mature further and to translocate to the adluminal surface. The remaining elongating spermatids at improper positions were finally phagocytosed by Sertoli cells. Furthermore, undifferentiated and abnormal spermatids exfoliated into the tubular lumen from adluminal surfaces. Thus, RA175-based cell junction is necessary for retaining elongating spermatids in the invagination of Sertoli cells for their maturation and translocation to the adluminal surface for timely release.

We thank Shigeki Yuasa for valuable scientific discussion and Hisae Kikuchi for technical advice.

This work was supported in part by Grants-in-Aid from the Ministry of Education, Science and Culture of Japan and by Research Grant 14A-1 for Nervous and Mental Disorders and Research on Brain Science from the Ministry of Health and Welfare of Japan, the Human Science Foundation. E.F. and Y.K. are Research Fellows of the Japan Society for the Promotion of Science.