Ultrastructure and motility of the caudal epididymis spermatozoa from the volcano mouse (Neotomodon alstoni alstoni Merriam, 1898).

The volcano mouse Neotomodon alstoni alstoni is a genus endemic to the higher elevations of the Mexican transvolcanic belt. In the present study we examined for the first time the morphological features of the spermatozoa taken from the caudal epididymis of this species by transmission and scanning electron microscopy. Spermatozoan motility was studied in sucrose and bicarbonate solutions; vitality and morphology were observed by light microscopy. Transmission electron microscopy shows that the head of spermatozoon is asymmetric and possesses a large and curved hook. The axoneme of the spermatozoan tail is highly developed at fibers 1, 5, and 6. Absolute and relative measurements of the length of the head, the midpiece, and the rest of the tail were also obtained. N. alstoni alstoni spermatozoa were hyperactive in the presence of 290 mM sucrose and 10 and 20 nM bicarbonate solutions exhibited high motility (180-190 microm/sec), and high flagellum beating frequency (10-12 Hz). In contrast, the spermatozoa in 310 mM sucrose solution showed scarce motility (13.5 +/- 3.8 microm/sec) and low beating frequency (1.5 +/- 0.4 Hz). It is proposed that the volcano mouse spermatozoa possess some features very similar to other mammalian spermatozoa and that bicarbonate triggers caudal epididymal sperm motility of this species. J. Exp. Zool. 287:316-326, 2000.

The P450 aromatase (P450 arom) gene is asymmetrically expressed in a critical period for gonadal sexual differentiation in the chick.

Steroid hormones appear to play an important role in gonadal sex differentiation of birds. Here we studied the steady-state level of the P450 arom mRNA by reverse transcriptase polymerase chain reaction (RT-PCR) in the left and the right presumptive ovary and testis of developing chicken embryos. The gonads were evaluated every hour during the undifferentiated period, at 144-156 h of incubation (h/i), and every 24 h after sexual differentiation at 168 and 192 h/i. Activity of P450 arom was determined by estrone production from [3H]androstenedione at 144-192 h/i. Moreover, morphological development of the gonad was also examined by light microscopy. Results show that onset of P450 arom mRNA and its protein activity were simultaneously detected in the left and the right ovaries at 147 h/i. Asymmetric function of P450 arom gene expression was observed at 156 h/i when morphological gonadal differentiation is first recognized. Biotransformation of [3H]androstenedione to estrone was also asymmetrically detected between the left and right gonad at 156 h/i and asymmetry was maintained throughout the analyzed stages. It is proposed that there is a gene in birds that is asymmetrically expressed in the undifferentiated stage of the female and the male gonad. In the female this gene could promote P450 arom gene expression, increasing estrogen production, which in turn could induce ovarian cortex proliferation and expression of other structural estrogen-regulated genes involved in ovarian sexual determination.

Delayed expression of the insulin-like growth factor I (IGF-I) gene in the XY sex-reversed female mouse ovary.

When the Y chromosome of Mus musculus domesticus (YDOM) mouse strain from Tirano (Italy) or Mus musculus poschiavinus (YPOS) from Poschiavo (Switzerland), is placed onto the C57BL/6J (B6) inbred background, the YDOM chromosome fails to induce normal testicular differentiation and instead allows development of ovaries and ovotestes in embryonic life. During postnatal development some hermaphroditic males become fertile whereas the XY females lack normal estrus cyclicity, produce low levels of gonadal steroids and cannot carry pregnancy to term. Here we studied the transcription of the IGF-I gene known to be involved in steroidogenesis. RNA was isolated from the XX and the XY ovaries at 1 to 40 d.p.p. and subjected to RT-PCR analysis. Immunocytochemical staining for IGF-I was performed to identify the cell type of IGF-I peptide localization, and protein expression was examined by Western blot analysis. The present results indicate that the IGF-I transcript was expressed at 1 d.p.p. in the XX ovary throughout the studied stages whereas in the XY ovary mRNA IGF-I was not detected until 15 d.p.p. IGF-I protein was identified in theca cells in the whole XX control ovary, while in the XY ovary, strong staining for IGF-I was found in the theca cells of the cortex. Faint staining was also seen around the medullary sterile cords. Western blot analysis showed normal onset in the XX and the XY ovary, but a different staining pattern for IGF-I in the XY ovary at 11 and 26 d.p.p. compared to the XX control ovary. We propose that delayed expression of IGF-I in the XY mouse ovary may be responsible for low steroid production and fertility problems in the XY sex-reversed adult female mouse.