ROS1 Signaling Regulates Epithelial Differentiation in the Epididymis

Abstract

The initial segment (IS) of the epididymis plays an essential role in male fertility. The IS epithelium is undifferentiated and nonfunctional at birth. Prior to puberty, the epithelium undergoes differentiation that leads to the formation of a fully functional organ. However, the mechanistic details of this program are not well understood. To explore this further, we used genetic engineering to create a kinase dead allele of the ROS1 receptor tyrosine kinase in mice and studied the effects of ROS1 tyrosine kinase activity on the differentiation of the IS epithelium. We show that the expression and activation of ROS1 coincides with the onset of differentiation and is exclusively located in the IS of the maturing and adult mouse epididymides. Here we demonstrate that the differentiation of the IS is dependent on the kinase activity of ROS1 and its downstream effector MEK1/2-ERK1/2 signaling axis. Using genetic engineering, we show that germ line ablation of ROS1 kinase activity leads to a failure of the IS epithelium to differentiate, and as a consequence sperm maturation and infertility were dramatically perturbed. Pharmacological inhibition of ROS1 kinase activity in the developing epididymis, however, only delayed differentiation transiently and did not result in infertility. Our results demonstrate that ROS1 kinase activity and the ensuing MEK1/2-ERK1/2 signaling are necessary for the postnatal development of the IS epithelium and that a sustained ablation of ROS1 kinase activity within the critical window of terminal differentiation abrogate the function of the epididymis and leads to sterility.

The expression and localization of V-ATPase and cytokeratin 5 during postnatal development of the pig epididymis

“…In addition, the orphan receptor tyrosine kinase ROS1, which is potentially activated by TLFs, is known as a key player in epithelial cell differentiation. Con- sistently, it has been demonstrated that male mice in which ROS1 has been knocked out using c-ROS1 oncogene 1 have undifferentiated epithelium [26]. Accordingly, it is probable that multiple factors are involved in the development and differentiation of pig epithelial cells.…”

PTEN signaling through RAF1 proto-oncogene serine/threonine kinase (RAF1)/ERK in the epididymis is essential for male fertility

“…Therefore, PTEN signaling is likely independent of ROS1 signaling. Because both PTEN and ROS1 (29) are upstream regulators of ERK signaling, it is possible that PTEN and ROS1 signaling are independent but converge to regulate ERK signaling, which, in turn, regulates differentiation of the initial segment.…”

Regulation of epithelial function, differentiation, and remodeling in the epididymis

“… 66 In the epididymis, ROS1 expression is very low at birth, but it becomes activated in the IS at the onset of epithelial cell differentiation. 67 68 Male mice KO for the c-ROS1 oncogene 1 ( c-ros1 KO), or ROS1 KM/KM mice carrying a kinase-dead allele of ROS1, the protein that is encoded by the c-ros1 gene, have an undifferentiated IS and are infertile, but have normal spermatogenesis. 26 67 Impaired differentiation of IS epithelial cells in the ROS1 KM/KM mice was demonstrated by a reduction of expression of AQP9, a “terminal differentiation” protein ( Figure 3 ), and a reduction in epithelial height, a hallmark of immature cells in this segment.…”

“… 26 67 Impaired differentiation of IS epithelial cells in the ROS1 KM/KM mice was demonstrated by a reduction of expression of AQP9, a “terminal differentiation” protein ( Figure 3 ), and a reduction in epithelial height, a hallmark of immature cells in this segment. 67 …”