236. Effects of long term recombinant rat follicle-stimulating hormone replacement on the restoration of spermatogenesis after chronic suppression of gonadotrophins in adult rats

Follicle stimulating hormone (FSH) in short-term rat studies supports spermatogenesis at multiple levels, notably spermatogonial development. The role of FSH in supporting full spermatogenesis in rats is still in question as long-term studies have not been possible due the development of neutralising antibodies to heterologous FSH preparations. This study sought to assess the effects of a homologous recombinant rat FSH (rr-FSH) preparation on the long-term restoration of spermatogenesis. Adult rats were GnRH-immunised (GnRH-im) for 12 weeks then, administered an anti-androgen; flutamide (flut), alone or together with rr-FSH (8µg/rat/daily) for 56 days (1 spermatogenic cycle). Germ and Sertoli cell numbers were quantified using an optical disector stereological method. Testis weight, serum FSH and inhibin B and Sertoli cell nuclear volume were significantly reduced to 15%, 13%, 25% and 57% of controls respectively, following GnRH-im+flut treatment. GnRH-im+flut treatment reduced A/I spermatogonial, type B spermatogonial+preleptotene, leptotene+zygotene and early pachytene spermatocyte numbers to 28%, 68%, 50% and 19% (P < 0.001) of controls respectively, with later germ cells rarely observed. After FSH treatment, no significant affect on testis weight, serum FSH and inhibin B or Sertoli cell number were observed. However, rr-FSH treatment significantly increased numbers of A/I spermatogonia, leptotene+zygotene and early pachytene spermatocytes from 28 = >42%, 50 = >69% and 19 = >27% of controls, respectively, while no differences were observed in later germ cell types. rr-FSH also increased (P < 0.05) the volume of Sertoli cell nuclei from 57 = >66% of control. In conclusion, FSH is unable to support full rat spermatogenesis; however, FSH can partially support germ cells notably spermatogonia through to early pachytene spermatocytes, despite the absence of androgenic support.

Synaptonemal complexes of triploid (ZZW) chickens: Z–Z pairing predominates over Z–W pairing

Twelve triploid, ZZW chickens of ages ranging from day 19 of incubation to 15 days after hatching were used for oocyte analysis. Oocytes show 117 axes per nucleus. At early pachytene, most axes form double synaptonemal complexes (triplets). An average of 27 triplets, 12 bivalents, and 12 univalents was observed. Later, a partial elimination of triplets occurs, as they are converted into typical trivalents or bivalents and univalents. The number of recombination nodules per nucleus (52.7) is similar to that of diploids. These nodules can occur in register in both central regions of a triplet (no lateral interference), and they probably stabilize the central region. Among 31 oocytes, 29 had a regular ZZ bivalent and a W univalent, and only 2 had triple pairing between a ZZ bivalent and a terminal region of the W axis (less than 1 μm in length and having a terminal recombination nodule). Competition for pairing between the gonosomes results in a large (93.5% of cases) predominance of Z–Z pairing, because of a relatively minor homology between the W and Z chromosomes. The prevailing pairing failure of the W chromosome may lead to early oocyte loss.Key words: sex chromosomes, triploids, synaptonemal complex, Z–W pairing, chicken, recombination nodules.

Synaptonemal complex analysis of hybrid cattle. I. Pachytene substaging and the normal full bloods

Meiotic chromosome pairing abnormalities in full-blood and hybrid Bos taurus and B. indicus cattle have been surveyed by electron microscopy of pachytene synaptonemal complex spreads. In this paper, the full-blood spreads are described in detail, including the use of XY and nucleolar morphology and other measured parameters for pachytene substaging. Pairing abnormalities were observed in up to 9% of the full-blood spreads. Most of these pairing abnormalities (83%) occurred in early-pachytene spreads, suggesting that the mechanism of synaptic adjustment may operate in cattle.Key words: synaptonemal complex, cattle, pachytene substages.

A nucleolar-organizing B chromosome showing segregation–distortion in the grasshopper Dichroplus pratensis (Melanoplinae, Acrididae)

A nucleolar-organizing B chromosome occurs at low frequency in some populations of the grasshopper Dichroplus pratensis. This B chromosome is telocentric, mitotically stable, and has a proximal secondary constriction. Haematoxylin and silver staining both demonstrate that the constriction organizes a nucleolus in addition to the standard nucleolar organizing region present in the S8 bivalent. In the single 2B male carrier studied, both B's organized nucleoli. The analysis of the meiotic behaviour of 1B males revealed that the B and the X chromosome associate preferentially during early prophase I. At leptotene the B and the X are associated in approximately 50% of the nuclei, but by zygotene – early pachytene the mean frequency of association is 86 reaching 100% in one male. This difference in association frequency between the two stages is highly significant. Persistent X–B associations lead to both chromosomes moving to the same pole in approximately 60% of the first anaphases. In the 2B male, both B's are paired in all early pachytene nuclei, while X–B associations seem to be random and much less frequent than in 1B males. Both B's remain associated in 60% of the metaphase I meiocytes, although true chiasmata do not seem to be involved. Nevertheless the B bivalent disjoins regularly. In 2B cells where both B's are univalents their segregation is random with respect to the X.Key words: B chromosome, nucleolus, nucleolar-organizing region, segregation–distortion, grasshopper.

Timing of sulphogalactolipid biosynthesis in the rat testis studied by tissue autoradiography

The testicular synthesis of sulphatoxygalactosylacylalkylglycerol (SGG) has been studied in the rat by autoradiography of frozen tissue sections following in vivo metabolic labelling. The results are consistent with the synthesis of this major mammalian germ-cell glycolipid at the zygotene and early pachytene stages of spermatogenesis. Further synthesis of SGG is prevented by the appearance of an inhibitor of galactolipid sulphotransferase activity at the mid-pachytene stage.

Fine structure and behaviour of a pericentric inversion in the sand rat, Psammomys obesus

In pachytene spermatocytes of the sand rat, Psammomys obesus, a long autosomal bivalent was observed, which was asynaptic for a large interstitial segment of its length in early pachytene. This bivalent also exhibited unaligned kinetochores. In late pachytene spermatocytes all autosomal bivalents were fully synapsed, but one of the shortest bivalents now possessed unaligned kinetochores. Evidence is presented in support of the proposition that the asynaptic interstitial region observed in early pachytene is due to the bivalent being heterozygous for a pericentric inversion. Using the maximum extent of homologous pairing, the break points were mapped at 26% from one end and 20% from the other. The unaligned kinetochores support the proposal that the aberration is an inversion and measurements of their positions confirm the estimated break points. In one cell a bivalent with interstitial (but no terminal) synapsis also confirms the inversion hypothesis. It is proposed that the bivalent is so small that topological considerations prevent the formation of the expected inversion loop. Evidence is also presented that complete synapsis of the bivalent during late pachytene can be attributed so ‘synaptic adjustment’, characterized by non-homologous synapsis (heterosynapsis). The position of the aberrant bivalent in relation to the sex chromosomes also changes during pachytene. When the bivalent is incompletely synapsed it generally associates by its ends with the ends of the sex chromosomes, but when it is non-changes during pachytene. When the bivalent is incompletely synapsed it generally associates by its ends with the ends of the sex chromosomes, but when it is non-homologously synapsed it is not associated with them.