C1q‐like 4 (C1QL4), a novel member of the C1q‐ and TNF‐related protein family, was found to be highly expressed in rodent and human testis. However, the localization, developmental, and hormonally regulated expression and biologic function of C1ql4 in the testis have not been investigated. Here, we demonstrated that C1ql4 mRNA and protein levels in murine testes gradually increased from the postnatal period to the adult stage and were up‐regulated by LH in vivo. In situ hybridization demonstrated that the distribution and expression levels of C1ql4 mRNA varied at different developmental stages, although C1ql4 mRNA was detected in the seminiferous tubule and interstitial Leydig cells. Recombinant C1QL4 did not affect cell proliferation but did increase testosterone production in TM3 Leydig cells, as well as in cultured seminiferous tubules. C1QL4‐induced testosterone secretion in Leydig cells was accompanied by increased expression of steroidogenic acute regulatory (StAR) protein and steroidogenic enzymes. During this process, the c‐Raf/extracellular signal‐regulated protein kinase kinases 1 and 2/ERK1/2/mitogen‐ and stress‐activated protein kinase‐1 and cAMP/PKA/cAMP‐responsive element binding protein signaling cascades were activated by C1QL4. The cell‐adhesion GPCR brain‐specific angiogenesis inhibitor 3 (BAI3), a putative receptor of C1QL4, was detected in the seminiferous tubule and interstitial Leydig cells during testicular development. Knockdown of Bai3 expression in Leydig cells led to a reduction in Star expression, accompanied by increases in phosphorylation of ERK1/2 and intercellular cAMP levels. However, C1QL4‐induced StAR expression was not completely suppressed in the Bai3‐deficient Leydig cells, and phosphorylation of ERK1/2 and intercellular cAMP levels were not significantly changed before and after C1QL4 stimulation. Our results suggested that although BAI3 played a role in C1QL4‐induced steroidogenesis, there was an unidentified receptor that mediated C1QL4‐activated testosterone secretion in Leydig cells through phosphorylation of ERK1/2 and up‐regulation of intracellular cAMP levels. Taken together, our results showed, for the first time to our knowledge, that C1QL4 served as a novel acute regulator of testosterone secretion, and BAI3 functioned as a new receptor that is involved in steroidogenesis in Leydig cells. BAI3‐independent ERK1/2 activation and cAMP activation mediated C1QL4‐induced testosterone secretion. This study expanded the reproductive roles and mechanisms of C1QL4 and BAI3 signaling pathways.—Tan, A., Ke, S., Chen, Y., Chen, L., Lu, X., Ding, F., Yang, L., Tang, Y., Yu, Y. Expression patterns of C1ql4 and its cell‐adhesion GPCR Bai3 in the murine testis and functional roles in steroidogenesis. FASEB J. 33, 4893–4906 (2019). http://www.fasebj.org

Ovarian aging is associated with depletion of the ovarian follicle reserve, which is the key determinant of fertility potential in females. In this study, we found that the small secreted protein C1QL1 is involved in the regulation of follicle depletion through intraovarian and endocrine control in a multidimensional collaborative manner. C1ql1 was detected to be conserved in the ovary and showed high transcript levels during folliculogenesis. Blockade of C1QL1 by intraperitoneal and ovarian intrabursal injection of C1QL1 antiserum into prepubertal mice impaired folliculogenesis accompanied by reductions in body weight, fat mass and intraovarian lipid accumulation. An elevation of circulating estradiol levels, reduction of hypothalamic KISS1 and GnRH expression and a decrease in serum FSH levels were found in C1QL1-deficient mice. In C1QL1-deficient ovaries, a large number of primordial follicles were recruited and developed into medium follicles, but underwent atresia at the large follicle stages, which resulted in depletion of follicle reserve. Depletion of C1QL1 alleviated the inhibitory effect of C1QL1 on granulosa cell apoptosis and the stimulatory effect of C1QL1 on granulosa cell autophagy, which resulted in accumulation in the preantral and early antral follicles and an increase in the atretic follicles. The abnormal profile of endocrine hormones accelerated the intraovarian effect of C1QL1 deficiency and further led to depletion of ovarian reserve. Altogether, this study revealed the expression patterns and the mechanism of action of C1QL1 during folliculogenesis, and demonstrated that deficiency of C1QL1 caused ovarian follicular depletion.

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