Hominoid-specific SPANXA/D genes demonstrate differential expression in individuals and protein localization to a distinct nuclear envelope domain during spermatid morphogenesis.

Human sperm protein associated with the nucleus on the X chromosome consists of a five-member gene family (SPANXA1, SPANXA2, SPANXB, SPANXC and SPANXD) clustered at Xq27.1. Evolved from an ancestral SPANX-N gene family (at Xq27 and Xp11) present in all primates as well as in rats and mice, the SPANXA/D family is present only in humans, bonobos, chimpanzees and gorillas. Among hominoid-specific genes, the SPANXA/D gene family is considered to be undergoing rapid positive selection in its coding region. In this study, RT-PCR of human testis mRNA from individuals showed that, although all SPANXA/D genes are expressed in humans, differences are evident. In particular, SPANXC is expressed only in a subset of men. The SPANXa/d protein localized to the nuclear envelope of round, condensing and elongating spermatids, specifically to regions that do not underlie the developing acrosome. During spermiogenesis, the SPANXa/d-positive domain migrated into the base of the head as the redundant nuclear envelope that protrudes into the residual cytoplasm. Post-testicular modification of the SPANXa/d proteins was noted, as were PEST (proline, glutamic acid, serine, and threonine rich regions) domains. It is concluded that the duplication of the SPANX-N gene family that occurred 6-11 MYA resulted in a new gene family, SPANXA/D, that plays a role during spermiogenesis. The SPANXa/d gene products are among the few examples of X-linked nuclear proteins expressed following meiosis. Their localization to non-acrosomal domains of the nuclear envelope adjacent to regions of euchromatin and their redistribution to the redundant nuclear envelope during spermiogenesis provide a biomarker for the redundant nuclear envelope of spermatids and spermatozoa.

Immunization against growth hormone releasing factor or chronic feed restriction initiated at 3.5 months of age reduces ovarian response to pulsatile administration of gonadotropin-releasing hormone at 6 months of age and delays onset of puberty in heifers.

A severe or moderate suppression of serum insulin-like growth factor I (IGF-I) was induced in heifers, beginning at 104 days of age, by active immunization against growth hormone-releasing factor (GRFi) or by chronic feed restriction (RES), respectively. We hypothesized that reduced serum IGF-I results in decreased serum estradiol-17 beta (E2), which in turn delays onset of puberty. The objectives of this experiment were to determine 1) whether GRFi and RES would alter follicular development and delay onset of puberty through similar mechanisms, and 2) whether GnRH would enhance follicular growth in control, GRFi, and RES heifers at 6 mo of age. Changes in IGF-I, somatotropin, LH, FSH, and E2 were evaluated. Serum IGF-I was greater in control than in RES heifers, and was greater in both these groups than in GRFi heifers by 169 days of age. Basal LH decreased in control and RES but not in GRFi heifers from 136 to 157 days of age. During the same period, a decrease in mean FSH was detected in control but not in GRFi and RES heifers. RES decreased mean serum E2 from 148 to 183 days of age. At 6 mo of age, pulsatile administration of GnRH (5 micrograms every 2 h for 42-46 h) increased serum LH and FSH similarly across treatments but had no effect on the number of follicles > or = 8 mm in GRFi and RES heifers relative to saline treatment. Serum E2 and IGF-I in follicular fluid from follicles > or = 8 mm were increased in all GnRH-treated heifers; however, concentrations of both hormones were lower in GRFi than in control or RES heifers. The main effect of treatments on serum IGF-I was reflected in follicles < or = 7 mm; follicular fluid IGF-I was greater in control than in RES heifers and was greater in both these groups than in GRFi heifers. Serum E2 was lower in RES than in control and GRFi heifers from 253 to 281 days of age. Because of an interaction, E2 was lower in GRFi-GnRH than in control-GnRH heifers but similar in GRFi-saline and control-saline heifers. By 393 days of age, 0% of RES and 32% of GRFi heifers had reached puberty compared to 71% of control heifers. These data support our hypothesis that decreased serum IGF-I results in decreased serum E2. GRFi appears to delay puberty in heifers because decreased serum IGF-I impairs the ovary's ability to synthesize preovulatory concentrations of E2, thereby delaying stimulation of an LH surge. In contrast, RES may delay puberty by delaying follicular development at two stages: a) decreased IGF-I in follicles < or = 7 mm may delay predominant follicular growth, and b) decreased LH may delay maturation of the preovulatory follicle.

Endocrine and ovarian responses to exogenous estradiol-17 beta in 6-month-old heifers previously immunized against growth hormone-releasing factor.

We hypothesized that estradiol-17 beta (E2) was capable of stimulating an LH surge in 6-mo-old heifers immunized against growth hormone-releasing factor (GRFi). To test this hypothesis Angus x Simmental heifers were immunized against GRF (n = 11) or human serum albumin (HSAi) (n = 6) at 113 d of age. Heifers were injected i.m. with 500 micrograms of E2 at 172 d of age. To characterize the LH response, samples were collected at frequent intervals for 1 h before and 32 h after E2. To assess ovarian responses, real-time ultrasonography was performed from d 9 to 20, and serum progesterone was evaluated from d 6 to 25 after E2, then weekly for 13 wk. Exogenous E2 stimulated (P < .001) LH surges, preceded by negative E2 feedback that decreased serum LH, in all GRFi and HSAi heifers. During the negative feedback period, serum LH was greater (P < .001), and the change in LH from before to after E2 was lower (P < .05), in GRFi than in HSAi heifers. Puberty occurred in 7/17 heifers within 66 d after receiving E2. We conclude that GRFi does not impair the release of an E2-induced LH surge, but it does decrease hypothalamo-hypophyseal sensitivity to the inhibitory effect of E2.