Talk:Paper - Abnormal pronuclei in the ferret (1936)

ABNORMAL PRONUCLEI IN THE FERRET By WILLIAM J. HAMILTON The Anatomical Department, St Thomas’s Hospital Medical School, London

AsnorMa pronuclear ova in Mammals are somewhat rare if we may judge from the number of specimens so far recorded. They have been described by R. van der Stricht (1911) in the cat, by Hill and Tribe (1924) in the cat, by Kremer (1924) in the mouse, and by Mainland (1980) in the ferret.

During my investigation of the “Early stages in the development of the ferret: fertilisation to the formation of the prochordal plate” (1934), I found in the material which I had collected three abnormal pronuclear stages. Two of the specimens were similar to those described by the above observers in that they had three pronuclei. In the third specimen there were four pronuclei present,

DESCRIPTION

Ova Nos. 1 and 2 were obtained from the same ferret at 444 hours after insemination; there were five other normal pronuclear stages in this ferret. Ovum No. 1 is present in eleven sections of 10 in thickness. The cytoplasm has a definite polar arrangement. Two of the pronuclei are of approximately the same size; they are in contact and eccentrically placed (Plate I, figs. 1 and 2). The other pronucleus is smaller and is lying at some distance from these in the deutoplasmic pole of the egg (Plate I, fig. 3). The chromatin granules in all of these pronuclei are well developed and appear to stain normally and are distributed on a definite reticulum. There is no indication in any of these pronuclei to show which is male and which female.

Ovum No. 2 is present in nine sections of 10 in thickness; it shows two pronuclei eccentrically placed and in contact and a third pronucleus lying at some distance from these. The polarity of the cytoplasm in this specimen is doubtful. Unlike Ovum No. 1, where the chromatin is well stained, this specimen has the chromatin poorly stained and the reticulum is absent. These pronuclei are apparently undergoing some degenerative change (Plate I, fig. 4); all the pronuclei show the same degree of degeneration.

Ovum No. 8 was obtained from a ferret 41} hours after insemination and is present in ten sections of 10 » in thickness. The cytoplasm exhibits a definite polarity. Four pronuclei are present in this specimen, two are lying near the protoplasmic pole but not in contact, whilst two others are lying in contact towards the equator of the egg. All the pronuclei in this specimen are small, the nuclear membranes are poorly defined, the chromatin granules are indistinct and the reticulum is not visible. 430 Wilham J. Hamilton

COMMENTS AND COMPARISONS

Supernumerary pronuclei do not appear to be very rare in the ferret, since I found three examples in a series of 124 early ova. I have not been able in the ferret to distinguish by their appearance or position the male and female pronuclei (Hamilton, 1934). In the case of the ovum described by R. van der Stricht (1911) in the cat, two of the pronuclei were situated in their normal position at the plastic half of the egg, whilst the third pronucleus was situated some distance from these. In each of the two abnormal ova described by Hill and Tribe (1924) in the cat, the supernumerary pronucleus was stated to be of approximately the same size as the larger of the other pronuclei (which were both eccentrically placed). They believed that the larger pronucleus was the male pronucleus. That supernumerary pronuclei may, be the result of fertilisation of binucleated ova was suggested and figured by Kremer (1924) in the mouse. This explanation, however, seems unlikely in the case of the ferret, since Mainland (1980), in the examination of 496 adult ovaries of the ferret, never found a binucleated ovum, nor did I in the examination of many ovaries. Ovum No. 1 described in this paper appears to be very similar to the trinucleated ovum described by Mainland (1930) in the ferret.

Now polyspermy is a normal phenomenon in the ova of Selachians, Reptiles and Birds (Brachet, 1985, and others), and the passage of supernumerary sperms into the ovum gives rise to supernumerary nuclei; but these nuclei soon degenerate, in some cases after abortive attempts to form asters. Further, polyspermy has been described in the mammal Ornithorhynchus by Gatenby and Hill (1924), and supernumerary sperms are often found in the perivitelline space of the ovum of the ferret and other Mammals at the early stages of fertilisation (see my former paper for a full description). Thus the occasional occurrence of supernumerary pronuclei may perhaps be attributable to the penetration of the vitelline membrane by more than one sperm.

The fact that all the pronuclei of one of my specimens are showing degenerative changes would seem to indicate that ova showing supernumerary pronuclei do not proceed far in development in the ferret, thus differing from those of animals in which polyspermy is physiological and in which only the supernumerary pronuclei degenerate.

I wish to record my thanks to Prof. A. B. Appleton of St Thomas’s Hospital Medical School for his valuable criticism.

REFERENCES

Bracuet, A. (1935). Traité d’ Embryologie des Vertébres. Masson et Cie, Paris.

Gatznsy, J. B. and Hirt, J. P. (1924). “Onan ovum of Ornithorhynchus exhibiting polar bodies

"and polyspermy.” Quart. J. micr. Sci. vol. Lxvim1, pt. 2.

Hamitton, W. J. (1934). ‘‘The early stages in the development of the ferret: fertilisation to the formation of the prochordal plate.” Trans. roy. Soc. Edinb. vol. Lvu11, pt. 1. Journal of Anatomy, Vol. LXX, Part 3

Fig. 1

HAMILTON—ABNORMAL PRONUCLEI IN THE FERRET

Plate I Abnormal Pronuclet in the Ferret 431

Hu, J. P. and Trine, M. (1924). “Early development of the cat (Felix Domestica).” Quart. J. micr. Sci. vol. LXV, pt. 4.

Kremer, J. (1924). ‘“‘Das Verhalten der Vorkerne im befruchteten Ei der Ratte und der Maus mit besonderer Beriicksichtigung ihrer Nucleolen.” Z. mikr.-anat. Forsch. Bd. 1.

Marntanp, D. (1930). “The early development of the ferret: the pronuclei.” J. Anat., Lond., vol. LxIVv, pt. 3.

Srricut, R. vAN DER (1911). “ Vitellogenése dans l’ovule de chatte.”” Arch. Biol., Paris, t. XXvI.

EXPLANATION OF PLATE I

Fig. 1. The sixth section of ovum No. 1 showing one complete pronucleus and part of another pronucleus.

Fig. 2. The seventh section of ovum No. 1 showing a pronucleus.

Fig. 3. The tenth section of ovum No. 1 showing the supernumerary pronucleus.

Fig. 4. The geventh section of ovum No. 2 showing two degenerating pronuclei in contact.