Contemporary genetic technologies and female reproduction

BACKGROUND

The Fifth Evian Annual Reproduction (EVAR) Workshop Meeting discussed knowledge regarding contemporary genetics in female reproduction.

METHODS

Specialist reproductive medicine clinicians and geneticists delivered presentations based on published literature and current research. The content of this report is based on the expert presentations and subsequent group discussions that took place during this Workshop.

RESULTS

Numerous ovarian genes with a role in infertility have been identified. Future challenges for genetic screening of patients, such as those with polycystic ovary syndrome, primary ovarian insufficiency or endometriosis, include the identification of high-throughput strategies and how to apply these findings to infertile patients. The identification of high-quality embryos in IVF using objective technologies remains a high priority in order to facilitate single-embryo transfer. Gene expression profiling of cumulus cells surrounding the oocyte, and proteomic and metabolomic approaches in embryo culture media may significantly improve non-invasive embryo quality assessment.

CONCLUSIONS

The way forward in advancing the knowledge of genes involved in reproduction was considered to be through genome-wide association studies involving large numbers of patients. Establishing international collaboration is required to enable the application of such technologies in sufficient numbers of patients.

233. A role for activin/inhibin in mouse gonocyte relocation and proliferation

Gonocytes in the testis resume proliferation after birth and relocate to contact the basement membrane of the seminiferous cords where they become spermatogonia. A previous in vitro study indicated that activin can increase gonocyte numbers on day 3 postpartum (dpp) rat testis, while the activin antagonist, follistatin, together with FSH, increased the number of spermatogonia (Meehan et al. 2000). The aim of this study was to understand how FSH, activin and inhibin, a potent activin antagonist, interact to influence gonocyte proliferation and relocation in the newborn mouse testis using in vivo and in vitro approaches. Two mouse models were analysed, the inhibin α knock out (inh a −/−) mouse and the InhbaBK mouse. The Inh a −/− mouse lacks inhibin, and thus activin acts unopposed by its most potent antagonist (Matzuk et al. 1992). The InhbaBK mouse has the Inhbb allele inserted into the Inhba locus, thus directing the expression of the less bioactive activin βB, in the spatiotemporal pattern of activin βA (Brown et al. 2000). In addition, an in vitro model was developed in which 1dpp wild type testis fragments were cultured in hanging drops for 24 h with the addition of combinations of activin, inhibin and FSH. Gonocyte proliferation in inh a −/− was assessed using proliferating cell nuclear antigen (PCNA). A significant increase in germ cell proliferation and relocation to the basement membrane was measured in 0dpp inh a −/−, while no difference was observed at 4dpp. The opposite was observed in InhbaBK mice, with reduced gonocyte migration in mutant animals at 0dpp. In vitro, inhibin seemed to inhibit proliferation and reduce the percentage of relocated gonocytes while FSH showed a tendency for the opposite effect on gonocyte migration. These findings show that inhibin levels affect germ cell development during early postnatal development in mouse testis influencing both cell maturation and proliferation. (1) Meehan T, Schlatt S, O'Bryan MK, de Kretser DM, Loveland KL. Regulation of germ cell and Sertoli cell development by activin, follistatin, and FSH. Dev Biol. 2000 Apr 15;220(2):225–37. (2) Matzuk MM, Finegold MJ, Su JG, Hsueh AJ, Bradley A. Alpha-inhibin is a tumour-suppressor gene with gonadal specificity in mice. Nature. 1992 Nov 26;360(6402):313–9. (3) Brown CW, Houston-Hawkins DE, Woodruff TK, Matzuk MM. Insertion of Inhbb into the Inhba locus rescues the Inhba null phenotype and reveals new activin functions. Nat Genet. 2000 Aug;25(4):453–7.

Sohlh1 is essential for spermatogonial differentiation

Spermatogonia are adult germline stem cells that can both self-renew and differentiate into spermatocytes. Little is known about factors necessary for spermatogonial differentiation. We identified a novel germ-cell-specific transcription factor that we named Sohlh1 (testis and ovary expressed basic helix-loop-helix (bHLH) transcription factor). In males, Sohlh1 is preferentially expressed in prespermatogonia and Type A spermatogonia. Loss of Sohlh1 causes infertility by disrupting spermatogonial differentiation into spermatocytes. Seven-day-old testes without Sohlh1 still express the testis-specific transcription factors Etv5, Taf4b, Zfp148, and Plzf, overexpress a novel Tohlh2 bHLH transcription factor, but lack LIM homeobox gene Lhx8 and show reduced expression of Ngn3. Sohlh1 represents the first testis-specific bHLH transcription factor that is essential for spermatogonial differentiation.

Discovery of germ cell-specific transcripts by expressed sequence tag database analysis

OBJECTIVE

To identify transcripts whose expression is restricted to germ cells.

DESIGN

Expressed sequence tags (ESTs) from unfertilized egg libraries were utilized to perform in silico subtraction and identify germ cell-specific transcripts.

SETTING

Baylor College of Medicine, Houston, Texas.

ANIMAL(S)

C57BL/6J/129SvEv hybrid.

INTERVENTION(S)

Tissue harvesting from mice.

MAIN OUTCOME MEASURE(S)

Identification of germ cell-specific transcripts.

RESULT(S)

We have used the Unigene collection of mouse cDNA libraries to identify ESTs derived from unfertilized egg libraries. A total of 3,499 ESTs were identified from Knowles Solter and Ko unfertilized egg cDNA libraries. In silico subtraction identified 258 ESTs, which were found in these unfertilized egg libraries, but not in adult mouse tissue cDNA libraries. We performed reverse transcription polymerase chain reaction (RT-PCR) on multiple adult tissues with 43 selected ESTs and found 5 of them where expression was absent in heart, lung, liver, brain, spleen, stomach, intestines, kidneys, and uterus, but restricted to ovaries and testes. Three ESTs were further analyzed, and they were exclusively localized to the oocytes by in situ hybridization.

CONCLUSION

We have shown that utilization of publicly available ESTs from murine EST libraries is a simple and rapid in silico approach to the identification of transcripts preferentially expressed in germ cells.

Functional conservation of atonal and Math1 in the CNS and PNS

To determine the extent to which atonal and its mouse homolog Math1 exhibit functional conservation, we inserted (beta)-galactosidase (lacZ) into the Math1 locus and analyzed its expression, evaluated consequences of loss of Math1 function, and expressed Math1 in atonal mutant flies. lacZ under the control of Math1 regulatory elements duplicated the previously known expression pattern of Math1 in the CNS (i.e., the neural tube, dorsal spinal cord, brainstem, and cerebellar external granule neurons) but also revealed new sites of expression: PNS mechanoreceptors (inner ear hair cells and Merkel cells) and articular chondrocytes. Expressing Math1 induced ectopic chordotonal organs (CHOs) in wild-type flies and partially rescued CHO loss in atonal mutant embryos. These data demonstrate that both the mouse and fly homologs encode lineage identity information and, more interestingly, that some of the cells dependent on this information serve similar mechanoreceptor functions.