Department of Biological Sciences, University of Memphis, Memphis, TN, USA.
Department of Chemistry, Faculty of Science, Mansoura University, Mansoura, Egypt.
Biol Reprod. 2021 Aug 3;105(2):491-502. doi: 10.1093/biolre/ioab083.
Sex determination requires the commitment of bipotential gonads to either a testis or an ovarian fate. Gene deletion of the kinase Map3k4 results in gonadal sex reversal in XY mice, and transgenic re-expression of Map3k4 rescues the sex reversal phenotype. Map3k4 encodes a large, multi-functional protein possessing a kinase domain and several, additional protein-protein interaction domains. Although MAP3K4 plays a critical role in male gonadal sex determination, it is unknown if the kinase activity of MAP3K4 is required. Here, we use mice expressing full-length, kinase-inactive MAP3K4 from the endogenous Map3k4 locus to examine the requirement of MAP3K4 kinase activity in sex determination. Although homozygous kinase-inactivation of MAP3K4 (Map3k4KI/KI) is lethal, a small fraction survive to adulthood. We show Map3k4KI/KI adults exhibit a 4:1 female-biased sex ratio. Many adult Map3k4KI/KI phenotypic females have a Y chromosome. XY Map3k4KI/KI adults with sex reversal display female mating behavior, but do not give rise to offspring. Reproductive organs are overtly female, but there is a broad spectrum of ovarian phenotypes, including ovarian absence, primitive ovaries, reduced ovarian size, and ovaries having follicles in all stages of development. Further, XY Map3k4KI/KI adults are smaller than either male or female Map3k4WT/WT mice. Examination of the critical stage of gonadal sex determination at E11.5 shows that loss of MAP3K4 kinase activity results in the loss of Sry expression in XY Map3k4KI/KI embryos, indicating embryonic male gonadal sex reversal. Together, these findings demonstrate the essential role for kinase activity of MAP3K4 in male gonadal sex determination.
性别决定需要将两性性腺分别向睾丸或卵巢命运方向进行决定。激酶 Map3k4 的基因缺失导致 XY 小鼠的性腺性别反转，而 Map3k4 的转基因重新表达挽救了性别反转表型。Map3k4 编码一种具有激酶结构域和几个额外蛋白-蛋白相互作用结构域的大型多功能蛋白。尽管 MAP3K4 在雄性性腺性别决定中起着关键作用，但尚不清楚 MAP3K4 的激酶活性是否是必需的。在这里，我们使用表达全长、激酶失活的 Map3k4 的小鼠，从内源性 Map3k4 基因座检查 MAP3K4 激酶活性在性别决定中的必要性。尽管 MAP3K4 的同源激酶失活（Map3k4KI/KI）是致命的，但一小部分能够存活到成年。我们表明 Map3k4KI/KI 成年动物表现出 4:1 的雌性偏倚性别比。许多成年 Map3k4KI/KI 表型雌性动物具有 Y 染色体。具有性别反转的 XY Map3k4KI/KI 成年动物表现出雌性交配行为，但不能产生后代。生殖器官明显是雌性的，但存在广泛的卵巢表型，包括卵巢缺失、原始卵巢、卵巢体积减小以及卵巢中具有所有发育阶段的卵泡。此外，XY Map3k4KI/KI 成年动物比雄性或雌性 Map3k4WT/WT 小鼠都小。在 E11.5 时对性腺性别决定的关键阶段进行检查表明，MAP3K4 激酶活性的丧失导致 XY Map3k4KI/KI 胚胎中 Sry 表达的丧失，表明胚胎雄性性腺性别反转。总之，这些发现表明 MAP3K4 激酶活性在雄性性腺性别决定中起着至关重要的作用。
