Inselman Amy, Handel Mary Ann
Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee, Knoxville, TN 37996-0840, USA.
Biol Reprod. 2004 Aug;71(2):570-8. doi: 10.1095/biolreprod.104.027938. Epub 2004 Apr 14.
Cellular and genetic approaches were used to investigate the requirements for activation during spermatogenesis of the extracellular signal-regulated protein kinases (ERKs), more commonly known as the mitogen-activated protein kinases (MAPKs). The MAPKS and their activating kinases, the MEKs, are expressed in specific developmental patterns. The MAPKs and MEK2 are expressed in all premeiotic germ cells and spermatocytes, while MEK1 is not expressed abundantly in pachytene spermatocytes. Phosphorylated (active) variants of these kinases are diminished in pachytene spermatocytes. Treatment of pachytene spermatocytes with okadaic acid (OA), to induce transition from meiotic prophase to metaphase I (G2/MI), resulted in phosphorylation and enzymatic activation of ERK1/2. However, U0126, an inhibitor of the ERK-activating kinases, MEK1/2, did not inhibit OA-induced MAPK activation or chromosome condensation. Analysis of spermatocytes lacking MOS, a mitogen-activated protein kinase kinase kinase responsible for MEK and MAPK activation, revealed that MOS is not required for OA-induced activation of the MAPKs. OA-induced MAPK activation was inhibited by butyrolactone I, an inhibitor of cyclin-dependent kinases 1 and 2 (CDK1, CDK2); thus, these kinases may regulate MAPK activity. Additionally, spermatocytes lacking CDC25C condensed bivalent chromosomes and activated both MPF and MAPKs in response to OA treatment; therefore, there is a CDC25C-independent pathway for MPF and MAPK activation. These studies reveal that spermatocytes do not require either MOS or CDC25C for onset of the meiotic division phase or for activation of MPF and the MAPKs, thus implicating a novel pathway for activation of the ERK1/2 MAPKs in spermatocytes.
采用细胞和遗传学方法研究细胞外信号调节蛋白激酶（ERKs，通常称为丝裂原活化蛋白激酶（MAPKs））在精子发生过程中的激活需求。MAPKs及其激活激酶MEKs以特定的发育模式表达。MAPKs和MEK2在所有减数分裂前的生殖细胞和精母细胞中表达，而MEK1在粗线期精母细胞中表达不丰富。这些激酶的磷酸化（活性）变体在粗线期精母细胞中减少。用冈田酸（OA）处理粗线期精母细胞，诱导其从减数分裂前期向中期I（G2/MI）转变，导致ERK1/2磷酸化和酶促激活。然而，ERK激活激酶MEK1/2的抑制剂U0126并未抑制OA诱导的MAPK激活或染色体浓缩。对缺乏MOS（一种负责MEK和MAPK激活的丝裂原活化蛋白激酶激酶激酶）的精母细胞进行分析，结果显示MOS并非OA诱导MAPKs激活所必需。OA诱导的MAPK激活被细胞周期蛋白依赖性激酶1和2（CDK1、CDK2）的抑制剂丁内酯I抑制；因此，这些激酶可能调节MAPK活性。此外，缺乏CDC25C的精母细胞在OA处理后会浓缩二价染色体并激活MPF和MAPKs；因此，存在一条不依赖CDC25C的MPF和MAPK激活途径。这些研究表明，精母细胞在减数分裂期开始或MPF和MAPKs激活过程中既不需要MOS也不需要CDC25C，从而暗示了精母细胞中ERK1/2 MAPKs激活的一条新途径。
