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Post-translational modification of proteins in the human testis development pathway.

BACKGROUND: The foetal testes produce the androgens necessary to masculinise the developing embryo and support the maturation of germ cells, that will eventually develop into sperm, thus ensuring future reproductive capacity. The testes develop from the bi-potential gonads in a highly orchestrated process resulting in the differentiation of a complex tissue with multiple cellular lineages. While recent transcriptomic and chromatin-based analyses of human foetal testes have provided an unprecedented level of insight into signalling pathways activated during this process, proteomic studies of the human foetal gonads remain limited. Proteins are active molecules and post-translational modification (PTM) of proteins influences protein activity, stability and localisation. Studies have shown that PTMs regulate critical proteins in testis development, and their disruptions are implicated in congenital disorders including differences of sex development (DSD), in which sex development is atypical. Despite this, the role and regulation of protein PTM during human testis development remains poorly understood due to limited access to human foetal gonadal tissue, a paucity of large-scale proteomics studies, and a lack of robust of human gonad in vitro models. OBJECTIVE AND RATIONALE: This review aims to provide a comprehensive analysis of validated PTMs affecting proteins critical for testicular development. We discuss PTMs with evidence for a role in normal testis development, and highlight those disrupted in DSD. We review emerging techniques, including proteomic technologies and organ modelling systems that may advance our understanding of PTMs in foetal testis development. We discuss challenges that have restricted the application of these technologies and how overcoming these will significantly improve our understanding of testis development and disease, diagnostics and patient outcomes. SEARCH METHODS: We searched PubMed and the University of Melbourne library for peer-reviewed English-language studies using keywords such as phosphorylation, SUMOylation, acetylation, ubiquitination alongside each protein of interest. PTM sites in proteins involved in testis development were identified using the PhosphoSitePlus database focusing those confirmed in in vitro or animal model studies. ClinVar and the Human Gene Mutation Database were used to identify patient variants that may disrupt PTM sites. OUTCOMES: Our review finds that proteins required for human foetal testis development are subject to extensive PTM. Several PTM sites and PTM-mediated pathways [e.g. MAPK (mitogen-activated protein kinase) pathway] are disrupted in patients with DSD or related conditions. While recent advances in proteomics technologies hold considerable promise, their application to human foetal gonads has been constrained by technical, ethical, and logistical challenges. Encouragingly, emerging high-sensitivity and low-input technologies, alongside stem cell-based approaches, offer viable pathways to overcoming these barriers. WIDER IMPLICATIONS: The relationship between gene regulation, protein expression, and cellular outcome is inherently non-linear, shaped by additional regulatory layers-most notably PTMs. The contribution of PTMs to human testis development in both typical and atypical contexts is a major knowledge gap. Addressing this gap has broad clinical and biological relevance: it may help improve genetic diagnosis or shed light on how proteins or pathways critical for testis development respond to environmental signals-an increasingly pressing question as declining global fertility rates bring testicular function under greater scrutiny. REGISTRATION NUMBER: N/A.

Humans

Mismatch repair protein MLH1 controls testis development by regulating the Hippo-YAP signaling pathway.

DNA mismatch repair (MMR) maintains genomic stability, and defects in MMR genes such as MLH1 and MSH2 predispose to cancer. Unlike other MMR components, MLH1 has unexplained roles in development, as Mlh1-deficient male mice exhibit severe testicular hypoplasia and sterility. Here, we uncover that MLH1 regulates testis development through the Hippo-Yes-associated protein (YAP) pathway. MLH1 directly binds YAP via its C-terminal domain and the WW domains of YAP, competitively inhibiting LATS1-mediated YAP phosphorylation. This interaction stabilizes YAP by suppressing ubiquitination and promotes its nuclear translocation dependent on MLH1's nuclear localization signal. Additionally, MLH1 facilitates YAP-TEAD complex formation, enabling expression of testicular development genes, including Wt1, Sox9, and Ctgf. These functions are independent of the MMR activity of MLH1. Mlh1-deficient mice show elevated YAP phosphorylation, reduced target gene expression, and impaired proliferation in developing testes. Pharmacological inhibition of the Hippo pathway kinases MST1/2 partially rescues testis hypoplasia in Mlh1-/- mice. These findings establish MLH1 as a Hippo pathway regulator and resolve its long-standing role in male gonad development.

Male

The distribution of poly(A)+ and poly(A)- protamine messenger RNA sequences in the developing trout testis.

Protamine messenger RNA was isolated in a very pure form from trout testes and used as a template for the synthesis of labeled complementary DNA (cDNA) of high specifiv activity. The cDNA was found to be a full-length transcript of protamine messenger RNA and was used as a probe for hybridization reactions with RNA preparations isolated from three subcellular compartments of differentiating trout testis cells. The RNA populations from the nuclei, polysomes, and postribosomal supernatant of these cells were fractionated into poly(A)-containing [poly(A)+] and poly(A)-free [poly(A)-] RNA to determine the distribution of these two forms of protamine mRNA in these cell compartments. At the early protamine stage of testis development, polysomal and postribosomal supernatant fractions contain almost equal quantities of poly(A)+ protamine mRNA, but poly(A)- protamine mRNA was found almost entirely in the polysomes.

Animals

Histone methylation. Its occurrence in different cell types and relation to histone H4 metabolism in developing trout testis.

Histone methylation in developing trout testis has been observed in the diploid stem cells and primary spermatocytes, which actively synthesize DNA and histones. In spermatids, histone methylation is minimal and so probably plays no role in the replacement of histones by protamine which is characteristic of this cell type. No turnover of histone methyl groups could be detected over several hours, so that unlike acetylation or phosphorylation of histones, methylation in this tissue appears to be a stable, irreversible modification. When histone H4, labeled with [14C]methyl groups, is separated on starch gels into acetylated and phosphorylated derivatives, [14C]methyl label does not appear in positions characteristic of newly synthesized histone H4, i.e. the highly acetylated (di-, tri-, and tetra-acetylated), unphosphorylated species. [14C]Methyl label appears rather in the unphosphorylated, and unacetylated or monoacetylated species, shifting with time to the monophosphorylated form of histone H4. These data suggest a temporal sequence of events for histone H4: synthesis, then acetylation and deacetylation, followed by methylation and phosphorylation. Occurring late after histone synthesis and assembly into chromatin, histone methylation might then be necessary for histone interactions with other molecules (e.g. histone phosphokinase) prior to mitosis.

Animals

Characterization of estrogen binding in the developing rat testis. Ontogeny of the testicular cytoplasmic estrogen receptor.

The properties and physical characteristics of a steroid binding component present in the immature (7 to 35 day) rat were investigated and found to be different from those of the 17 beta-estradiol receptor in the mature rat testis. These properties include a binding capacity of 483 fmol estradiol/mg protein, a Ka at equilibrium of 4.23 x 10(7)M-1, and broad steroid specificity as shown by interaction with several steroids; no binding was observed with diethylstilbestrol. The component, found in blood and several tissues including the testis, migrated as a 4.6S peak on sucrose gradients. This 4.6S component, which interacted with an anti-alphafetoprotein antiserum, decreased with age and was not detectable in the testis after day 21 or in the serum after day 25. These data suggest that this component is alphafetoprotein. Ontogenic appearance of the testicular cytoplasmic 17 beta-estradiol receptor in the developing rat was further elucidated. Sucrose gradient sedimentation analysis of cytosols revealed an 8S binding component that was first detectable at 23 days. Specific binding (fmol [3H]-estradiol/testis) was relatively low in neonates, rose to 59 fmol during the third week, and increased dramatically to 333 fmol at 7 weeks; binding rose only gradually after maturity. The receptor was tissue specific and steroid specificity studies demonstrated that only diethylstilbestrol and other estrogens were effective in competing with 17 beta-estradiol for binding sites. The Ka at equilibrium was determined as 3 x 10(10)M-1 and the binding sites were saturable in an in vitro system. The receptor did not interact with anti-alphafetoprotein antiserum as indicated by sucrose gradient studies. These data demonstrate the developmental appearance of the testicular cytoplasmic estradiol receptor in the immature rat.

Aging

Properties of chromatin subunits from developing trout testis.

When a sample of trout testis nuclei is digested with micrococcal nuclease, the DNA is cleaved almost entirely to discrete fragments approximately 200 base pairs long and multiples thereof. The same DNA fragments can be obtained when isolated chromatin, as opposed to intact nuclei, is nuclease digested. These DNA fragments can also be found in discrete chromatin "subunits" isolated from nuclease-digested nuclei. Sedimentation through sucrose gradients or velocity sedimentation in an analytical ultracentrifuge separates these chromatin subunits into 11 S (monomer), 16 S (dimer), and 22 S (trimer) etc. species. Subunits can also be fractionated on a Sepharose 2B column equilibrated and run in low salt. High salt (greater than 40 mM NaCl) or divalent cations (congruent to 5 mM) cause subunit precipitation. Chromatin subunits have a protein to DNA ratio of approximately 1.2 and contain all the histones, including the trout-specific histone T. There are, however, no detectable nonhistone chromosomal proteins. Mg-2+ precipitates of the 11 S chromatin monomers, when pelleted, are thin and clear, while oligomer Mg-2+ pellets are thick and white. This could reflect a more symmetrical or ordered packing of 11 S monomers, which are deficient in histone I. This histone may cross-link the larger oligomers, resulting in a disordered Mg-2+ complex. These results are consistent with the subunit model of chromatin structure, based on 200 base pair long regions of DNA associated with histones. These subunits would be separated by nuclease-sensitive DNA spacer regions and cross-linked by histone I.

Animals

Sites of in vivo histone methylation in developing trout testis.

Specific lysyl residues of trout testis histones H3 and H4 are methylated partially during rainbow trout spermatogenesis. Histones H1, H2A, H2B, and protamine are not methylated. The single site (lysine 20) in histone H4 and the two major sites (lysines 9 and 27) in histone H3 are homologous to those determined for other organisms, but an additional minor site (lysine 4) occurs in histone H3. As described for calf thymus, both histones H3 and H4 contain epsilon-N-mono- and dimethyllysine, while histone H3 contains in addition, epsilon-N-trimethyllysine. The trout-specific histone H6, which accounts for 0.5 to 1.0% of total histone, contains a sequence for residues 3 to 5,-Arg-Lys-Ser-, which is the same as one methylated in histones H3, at lysines 9 and 27. However, histone H6 yields only trace amounts of [3H]methyl incorporation and no detectable methyllysines on amino acid analysis.

Alanine

[Tubular structure and germ cell distribution of cryptorchid or normal testes in early childhood (author's transl)].

INTRODUCTION: Many recent publications have demonstrated that the cryptorchid testicle (and, to a lesser extent, the descended partner) are progressively injured from the second year of life onwards. Do these injuries occur in an organ which has been healthy up to this time or are they superimposed on a structurally abnormal testicle? In order to answer this, parts of cryptorchid testicles, of the descended partners, and of normal testicles were compared by histological examination of serial sections. MATERIAL AND METHODS: Parts of four testes from children aged 4-7 months (2 specimens obtained by biopsy and 2 from autoptic material) and parts of four testes from children 1 1/2 years old (2 obtained by biopsy and 2 from autoptic material) were examined. The biopsies were fixed in Stieve's fixative. Tissue samples from clinically healthy children who had died suddenly were fixed in 4% formalin. The tissue was embedded in paraffin and sectioned serially; 6 mum sections were stained with HE. The spermatogonia in each cross-section and in each oblique section of a same tubule were counted and the counts of the latter were adjusted to a cross-section 50-60 mum in diameter. This counting technique did not alter the density of spermatogonia. The graphs present data on the density of spermatogonia through the lengths of the tubules examined and demonstrate tubular branching and blind ends. In the first year of life the cryptorchid testis and its descended partner showed repeated long sections lacking spermatogonia in the same tubule, whereas in normal testes the spermatogonia were more evenly distributed. The cryptorchid testis showed increased tubule branching in the areas examined. In the second year of life the tubules of the cryptorchid testis and its descended partner manifest areas free of germ cells, increased branching, and blind ends. The cryptorchid testis also had a tubule completely free of spermatogonia. The germ cell-free parts were always associated with a smaller tubule diameter than normal. The normal testes did not disclose increased branching or spermatogonium-free areas within similar lengths of tubules and showed an even distribution of spermatogonia. DISCUSSION: The different distribution of spermatogonia within the tubules and the increased branching of the tubules in cryptorchid testes indicate a previous disturbance of testis development.

Age Factors

Production and effects of 7 alpha-hydroxytestosterone on testosterone and dihydrotestosterone metabolism in rat testis.

1. Testicular 7 alpha-hydroxylation of testerone was assayed in cell extracts of rats between 12 and 79 days of age. Maximal 7 alpha-hydroxylase activity was observed about 60 days, while insignificant activity was obtained prior to 42 days of age. 2. 7 alpha-Hydroxytestosterone, a major metabolite of testosterone in mature rat testis, inhibited 5 alpha-reduction of testosterone in cell extracts of mature but not of immature rat testis. 3. Maximal testicular activity of 3 beta-hydroxysteroid dehydrogenase using dihydrotestosterone as substrate was obtained in the presence of NAD, while maximal 3 alpha-hydroxysteroid dehydrogenase activity was observed with NADP. Both enzyme activites were reversible. 4. Sensitivity toward testosterone inhibition of 3-hydroxysteroid dehydrogenase varied greatly with stage of testis development being highest at 25-27 days of age. In contrast to testosterone, 7 alpha-hydroxytestosterone was an inhibitor of 3 alpha-hydroxysteroid dehydrogenase only. In the mature rat testis 7 alpha-hydroxytestosterone may be a naturally occurring inhibitor of dihydrotestosterone and 5 alpha-androstane-3 alpha, 17 beta-diol formation.

Aging

Testis differentiation in the fetal and postnatal ferret.

Testis development has been examined in a series of 59 fetal and 9 postnatal ferrets from day 22 of the 40-42 day pregnancy, to 12 days after birth. Developing seminiferous tubules and interstitial cells were first seen on day 26, and were well established one day later. Differentiation was associated with cell enlargement and cell division, and consequently the testes grew distinctly more rapidly at this time than the corresponding ovaries. Up to the end of pregnancy the epithelioid interstitial cells, derived from stromal tissue, formed a large proportion of the testis. Lipid was distinguishable in them, histologically, from about day 30. As in various other mammals, there appeared to be some regression of the interstitial Leydig cells around the time of birth, when the seminiferous tubules resumed their growth. The intra-gonadal rete was present from day 22 onwards; it established connexions with the seminiferous tubules through the small tubuli recti by day 32.

Age Factors

Orchiopexy in prepubertal boys. Five-year survey.

A series of 141 prepubertal boys with undescended testes operated on in a provincial teaching hospital has been analyzed five years after operation. The main features noted at presentation were the mature age of the patients and the small number of boys referred by pediatricians. The incidence of unsatisfactory results was 36% in unilateral and 35% in bilateral operations. The majority of the patients (81%) were referred for surgery after the age of five years, commonly regarded as the most suitable time for surgical correction. Three patients required a primary orchiectomy for a small atrophic testis, while 2 patients had an orchiectomy done on a previously operated testis. The complication rate for the series was 4.5%. Testicular biopsy was not done at the time of operation, and no patients were referred for semen analysis. Eight patients underwent a second orchiopexy after the first operation failed. In 6 patients an atrophic testis developed after the second procedure. The need for more than one postoperative examination is stressed in view of the fact that an initially favorable result may not persist since the testes may be found, at a later date, to have retracted into an unsatisfactory position. The reasons for the poor results are discussed and compared briefly with previous reports.

Adolescent

Abnormalities of the vas deferens and epididymis in cryptorchid boys with congenital rubella.

Cryptorchidism was present in 12% of 316 boys with congenital rubella (CR) followed by The Roosevelt Hospital Rubella Project. Eight of these patients, age 4 through 16 yr, had a recent orchiopexy, 4 on the left, 2 on the right, and 2 bilaterally. The vasoepididymal system was absent or apparently obstructed in 60% of the 10 sides. The epididymis was abnormal in 6 instances and the vas deferens in 5. Sixty-one boys of the entire series had an intravenous pyelogram (IVP) that was significantly abnormal in 18%. The 8 patients described all had a normal IVP except for 2 who had a malrotated kidney on the involved side. In 5 of the 8, a known maternal rubella infection has occurred during the first 8 wk of gestation. As the rubella virus is known to interfere with cellular growth and tissue differentiation in early pregnancy, it apparently altered the developing testis and mesonephric duct system. Similar vasoepididymal abnormalities have been described previously in patients with uncomplicated cryptorchidism, inguinal hernia, kidney defects, cystic fibrosis and male sterility. Their presence should alert the clinician to perform an IVP and also consider a diagnosis of congenital rubella.

Adolescent