Vax1 Heterozygous Mice Exhibit Male and Female Subfertility: Central Versus Peripheral Origins

Presentation Number: PP30-2
Date of Presentation: June 23rd, 2014

Hanne M Hoffmann*1, Anika Tamrazian1 and Pamela L Mellon2
1Univ of California San Diego, La Jolla, CA, 2Center for Circadian Biology, University of California, San Diego, La Jolla, CA

Abstract

Sexual maturation and fertility are regulated by the hypothalamic pituitary gonadal (HPG) axis. Improper development or disruption of the HPG axis leads to reduced fertility or complete infertility. In this study, we show that the homeodomain transcription factor Ventral Anterior Homeobox1 (Vax1) is expressed in adult mouse male and female pituitary, hypothalamus, and testis. We hypothesize that Vax1 is required for normal fertility by regulating the HPG axis in mice. Since Vax1-/- mice die soon after birth, we conducted a fertility study in Vax1+/- mice. We found both Vax1+/- males and females produced fewer pups/litter and females produced fewer litters as compared to wild type. To determine the origin of this subfertility, we analyzed gene expression patterns from the hypothalami and pituitaries from 2-5 month old male and diestrus female Vax+/- mice. Vax1 mRNA levels were reduced, as expected. Males exhibited a 69% decrease in GnRH transcript levels and females an 80% reduction. Furthermore, there was a ~70% reduction in GnRH neuron numbers in both male and female mice as determined by IHC. Interestingly, qRT-PCR from the pituitary showed that LH, FSH and GnRH receptor transcript levels were reduced in females only. To establish if the altered transcript levels affected circulating hormone levels, we measured LH and FSH in sera collected from these same animals. Once more, only females were affected and presented high circulating LH levels. As both LH and FSH are required for proper maturation and release of follicles, we evaluated the number of corpora lutea in diestrus Vax1+/- females. H&E staining found fewer corpora lutea in the Vax1+/-, indicating a reduction in ovulated oocytes, which is in agreement with the reduced litter size of these females. We propose that Vax+/- females are subfertile due to a reduction in GnRH transcript level and GnRH neuron numbers along with a reduction of pituitary GnRH receptor mRNA. These changes would result in a blunted GnRH signal to the pituitary leading to abnormal LH levels possibly resulting in fewer corpora lutea and reduced fertility. In contrast, Vax1+/- male subfertility did not appear to have a central origin as all of the studied pituitary and hypothalamic transcripts, as well as circulating LH, FSH and T levels were comparable to controls. While H&E stained testis revealed normal morphology, Vax1+/- mice had an 88% reduction of motile sperm. Staining for LacZ in Vax1-LacZ mice showed that the elongated spermatids in the testis activate the Vax1 promoter, though Vax1 mRNA expression was absent in epididymal sperm as determined by qRT-PCR. Our data support that Vax1, expressed in sperm, is required for normal sperm generation, though it is still unclear what role Vax1 plays in sperm generation and maturation. In conclusion, reduced expression of Vax1 is associated with sub-fertility in adulthood of both male and female mice.

 

Nothing to Disclose: HMH, AT, PLM